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Polyakov Loop at Finite Temperature in Chiral Quark Models: At finite temperature, chiral quark models do not incorporate large gauge
invariance which implies genuinely non-perturbative finite temperature gluonic
degrees of freedom. Motivated by this observation, we describe how the coupling
of the Polyakov loop as an independent degree of freedom to quarks not only
accounts for large gauge invariance, but also allows to establish in a
dynamical way the interaction between composite hadronic states such as
Goldstone bosons to finite temperature non-perturbative gluons in a medium
which can undergo a confinement-deconfinement phase transition. | hep-ph |
Systematics of parton-medium interaction from RHIC to LHC: Despite a wealth of experimental data for high-P_T processes in heavy-ion
collisions, discriminating between different models of hard parton-medium
interactions has been difficult. A key reason is that the pQCD parton spectrum
at RHIC is falling so steeply that distinguishing even a moderate shift in
parton energy from complete parton absorption is essentially impossible. In
essence, energy loss models are effectively only probed in the vicinity of zero
energy loss and, as a result, at RHIC energies only the pathlength dependence
of energy loss offers some discriminating power. At LHC however, this is no
longer the case: Due to the much flatter shape of the parton p_T spectra
originating from 2.76 AGeV collisions, the available data probe much deeper
into the model dynamics. A simultaneous fit of the nuclear suppression at both
RHIC and LHC energies thus has great potential for discriminating between
various models that yield equally good descriptions of RHIC data alone. | hep-ph |
Matching the Low and High Energy Determinations of $α_s(M_z)$ in
the MSSM: Recent calculations of supersymmetric corrections to the conflicting ratios
$R_b$ and $R_c$ have shown that an alleged discrepancy between the SM
predictions of these observables and the corresponding experimental values can
be cured in the MSSM within a certain region of the parameter space. Here we
show that, in this very same region, also a well-known discrepancy between the
low and high energy determinations of $\alpha_s(M_Z)$ can be disposed of.
Specifically, we find that the lineshape determination of the strong coupling
constant, which in the SM points towards the large central value $\alpha_s(M_Z)
\stackrel{\scriptstyle >}{{ }_{\sim}} 0.125$, can be matched up with the value
suggested by the wealth of low-energy data, namely $\alpha_s(M_Z) \simeq 0.11$,
which is smaller and more in line with the traditional QCD expectations at low
energy. Our approach differs from previous analyses in that we argue that the
desired matching could originate to a large extent from a purely electroweak
supersymmetric quantum effect. | hep-ph |
Model-Independent Global Constraints on New Physics: Using effective-lagrangian techniques we perform a systematic survey of the
lowest-dimension effective interactions through which heavy physics might
manifest itself in present experiments. We do not restrict ourselves to special
classes of effective interactions (such as `oblique' corrections). We compute
the effects of these operators on all currently well-measured electroweak
observables, both at low energies and at the $Z$ resonance, and perform a
global fit to their coefficients. Despite the fact that a great many operators
arise in our survey, we find that most are quite strongly bounded by the
current data. We use our survey to systematically identify those effective
interactions which are {\it not} well-bounded by the data -- these could very
well include large new-physics contributions. Our results may also be used to
efficiently confront specific models for new physics with the data, as we
illustrate with an example. | hep-ph |
Meson-like Baryons and the Spin-Orbit Puzzle: I describe a special class of meson-like \Lambda_Q excited states and present
evidence supporting the similarity of their spin-independent spectra to those
of mesons. I then examine spin-dependent forces in these baryons, showing that
predicted effects of spin-orbit forces are small for them for the same reason
they are small for the analogous mesons: a fortuitous cancellation between
large spin-orbit forces due to one-gluon-exchange and equally large inverted
spin-orbit forces due to Thomas precession in the confining potential. In
addition to eliminating the baryon spin-orbit puzzle in these states, this
solution provides a new perspective on spin-orbit forces in all baryons. | hep-ph |
The mass spectrum and strong decays of isoscalar tensor mesons: In this work, we present a systematic study of the observed isoscalar tensor
$f_2$ states. With the detailed analysis of the mass spectrum and calculation
of the $f_2$ two-body strong decays, we extract information of their underly
structures, and try to categorize them into the conventional tensor meson
family ($n^{3}P_{2}$ $(n=1,2,3,4)$ and $m^{3}F_{2}$ ($m=1,2$)). We also give
predictions for other decay modes of these tensor mesons, which are useful for
further experimental investigations. | hep-ph |
Bayesian fit analysis to full distribution data of $\bar B \to D^{(*)}
\ell\barν$: $|V_{cb}|$ determination and New Physics constraints: We investigate the semi-leptonic decays of $\bar B \to D^{(*)} \ell\bar\nu$
in terms of the Heavy-Quark-Effective-Theory (HQET) parameterization for the
form factors, which is described with the heavy quark expansion up to $\mathcal
O(1/m_c^2)$ beyond the simple approximation considered in the original CLN
parameterization. An analysis with this setup was first given in the
literature, and then we extend it to the comprehensive analyses including (i)
simultaneous fit of $|V_{cb}|$ and the HQET parameters to available
experimental full distribution data and theory constraints, and (ii) New
Physics (NP) contributions of the $V_2$ and $T$ types to the decay
distributions and rates. For this purpose, we perform Bayesian fit analyses by
using Stan program, a state-of-the-art public platform for statistical
computation. Then, we show that our $|V_{cb}|$ fit results for the SM scenarios
are close to the PDG combined average from the exclusive mode, and indicate
significance of the angular distribution data. In turn, for the $\text{SM} +
\text{NP}$ scenarios, our fit analyses find that non-zero NP contribution is
favored at the best fit point for both $\text{SM} + V_2$ and $\text{SM} + T$
depending on the HQET parameterization model. A key feature is then realized in
the $\bar B \to D^{(*)} \tau\bar\nu$ observables. Our fit result of the HQET
parameters in the $\text{SM} (+T)$ produces a consistent value for $R_D$ while
smaller for $R_{D^*}$, compared with the previous SM prediction in the HFLAV
report. On the other hand, $\text{SM}+V_2$ points to smaller and larger values
for $R_D$ and $R_{D^*}$ than the SM predictions. In particular, the $R_{D^*}$
deviation from the experimental measurement becomes smaller, which could be
interesting for future improvement on measurements at the Belle II experiment. | hep-ph |
The electromagnetic Sigma-to-Lambda hyperon transition form factors at
low energies: Using dispersion theory the low-energy electromagnetic form factors for the
transition of a Sigma to a Lambda hyperon are related to the pion vector form
factor. The additionally required input, i.e. the two-pion--Sigma--Lambda
amplitudes are determined from relativistic next-to-leading-order (NLO) baryon
chiral perturbation theory including the baryons from the octet and optionally
from the decuplet. Pion rescattering is again taken into account by dispersion
theory. It turns out that the inclusion of decuplet baryons is not an option
but a necessity to obtain reasonable results. The electric transition form
factor remains very small in the whole low-energy region. The magnetic
transition form factor depends strongly on one not very well determined
low-energy constant of the NLO Lagrangian. One obtains reasonable predictive
power if this low-energy constant is determined from a measurement of the
magnetic transition radius. Such a measurement can be performed at the future
Facility for Antiproton and Ion Research (FAIR). | hep-ph |
Search for New Physics in Rare Top Decays: Top physics provides a fertile ground for new-physics searches. At present,
most top observables appear to be in good agreement with the respective
Standard Model predictions. However, in the case of decay modes that are
suppressed in the Standard Model, new-physics contributions of comparable
magnitude may exist and yet go unnoticed because their impact on the total
decay width is small. Hence it is interesting to probe rare top decays. This
analysis focuses on the decay $t \to b \bar b c$. Useful observables are
identified and prospects for measuring new-physics parameters are examined. | hep-ph |
Pair Production of Doubly-Charged Scalars: Neutrino Mass Constraints and
Signals at the LHC: We study the pair production of doubly charged Higgs bosons at the Large
Hadron Collider (LHC), assuming the doubly charged Higgs to be part of an
SU(2)_L triplet which generates Majorana masses for left-handed neutrinos. Such
pair-production has the advantage that it is not constrained by the triplet
vacuum expectation value, which tends to make the single production rate rather
small. We point out that, in addition to the Drell-Yan (DY) production
mechanism, two-photon processes also contribute to H++H++ production at a level
comparable to the QCD corrections to the DY channel. Decays of the doubly
charged Higgs into both the l+l+ and W+W+ modes are studied in detail to
optimize the signal observation over the backgrounds. Doubly charged scalars
should be observable at the LHC with 300 fb^-1 integrated luminosity in the ll
channel upto the mass range of 1 TeV even with a branching fraction of about 60
%, and in the WW channel upto a mass of 700 GeV. Such a doubly charged Higgs,
if it is a member of a triplet generating neutrino masses,cannot be long-lived
on the scale of collider detectors although it might lead to a displaced
secondary vertex during its decay if it is lighter than about 250 GeV. | hep-ph |
Gluon Radiation in $t\bar t$ Production and Decay at the LHC: Understanding the pattern of gluon radiation in $t \bar t$ production and
decay processes is important for making an accurate determination of the top
mass from the momenta of its decay products. The larger energy of the LHC $pp$
collider boosts the top cross section by a factor of 100 compared to that at
the Tevatron, but it also increases the amount of additional gluon radiation.
We calculate the cross section for gluon radiation in top production and decay
at the LHC. The distributions of this radiation are presented and the exact
matrix-element results are compared with results from the HERWIG parton-shower
Monte Carlo. | hep-ph |
A bound on Universal Extra Dimension Models from up to 2fb^{-1} of LHC
Data at 7TeV: The recent up to 2fb^{-1} of data from the ATLAS and CMS experiments at the
CERN Large Hadron Collider at 7TeV put an upper bound on the production cross
section of a Higgs-like particle. We translate the results of the H -> WW -> l
nu l nu and H -> gamma gamma as well as the combined analysis by the ATLAS and
CMS into an allowed region for the Kaluza-Klein (KK) mass M_{KK} and the Higgs
mass $M_H$ for all the known Universal Extra Dimension (UED) models in five and
six dimensions. Our bound is insensitive to the detailed KK mass splitting and
mixing and hence complementary to all other known signatures. | hep-ph |
The Top Quark and other Fermion Masses: Recent developments on approaches to the quark lepton mass problem are
reviewed. In particular we discuss dynamical calculations of the top quark mass
at (a) the infrared quasifixed point of the Minimal Supersymmetric Standard
Model renormalisation group equations, and (b) a strongly first order critical
point of the Standard Model effective potential. The phenomenology of symmetric
mass matrix ans\"{a}tze with texture zeros at the unification scale is also
considered. The underlying chiral symmetry presumed responsible for the fermion
mass hierarchy is discussed, with particular reference to superstring based
models. | hep-ph |
Vector-like Quarks: In this talk we emphasise the importance of vector-like quarks (VLQs) and
their potential to solve some of the open questions of the Standard Model.
These are, in some sense minimal extensions of the Standard Model, that can be
probed in the next round of experiments. We also make an analogy between
vector-like quarks(VLQs) and right-handed neutrinos, emphasising that in both
cases some of the flavour dogmas of the SM are violated in a controlled way. | hep-ph |
Matter-antimatter origin of cosmic magnetism: We explore the hypothesis that the abundant presence of relativistic
antimatter (positrons) in the primordial universe is the source of the
intergalactic magnetic fields we observe in the universe today. We evaluate
both Landau diamagnetic and magnetic dipole moment paramagnetic properties of
the very dense primordial electron-positron $e^{+}e^{-}$-plasma, and obtain in
quantitative terms the relatively small magnitude of the $e^{+}e^{-}$ magnetic
moment polarization asymmetry required to produce a consistent
self-magnetization in the universe. | hep-ph |
B^0_{d,s} - \bar{B}^0_{d,s} mixing in the model III 2HDM: In the model III 2HDM there are new CP violating phases which would affect
the $B_{d,s}^0 - \bar{B}_{d,s}^0$ mixing. In this paper, we calculate the new
physics contributions to the neutral B meson mass splitting $\Delta M_{B_q}$
(q=d, s) at the next-to-leading order (NLO) level. Using the high accuracy data
and other relevant data, we draw the constraints on the parameter space of the
model III 2HDM. Moreover, we calculate the new physics corrections to the ratio
$q/p$. It is found that the phase of $(q/p)_n$ for $B_d$ which is due to the
new contributions is very small and consequently in agreement with the
measurements of the time dependent CP asymmetry $S_{J/\psi K}$ in $B\to J/\psi
K_S$. On the contrary, the phase of $(q/p)_n$ for $B_s$ is large enough to give
significant effects on CP violation in the neutral $B_s$ system. | hep-ph |
Phenomenology of light remnant doubly charged Higgs fields in the
supersymmetric left-right model: It has recently shown that in supersymmetric left-right models with automatic
R-parity conservation, the theory below the $W_R$ scale is given by MSSM with
massive neutrinos and a pair of doubly charged superfields with masses in the
100 GeV range (with or without an extra pair of heavy Higgs doublets (M \geq 10
TeV) depending on the model). In this paper we study the unification prospects
for such theories and their phenomenological implications for collider
experiments. We study two versions of the theory, one with supersymmetry
breaking transmitted via the gauge and another where the same occurs via
gravitational forces. We point out that looking at multi $\tau$ final states
can considerably constrain the parameter space of the model. | hep-ph |
Jet angularities in photoproduction at the Electron-Ion Collider: We consider the one-parameter family of jet substructure observables known as
angularities using the specific case of inclusive jets arising from
photoproduction events at an Electron-Ion Collider (EIC). We perform numerical
calculations at next-to-leading logarithmic accuracy within perturbative QCD
and compare our results to PYTHIA 6 predictions. Overall, we find good
agreement and conclude that jet substructure observables are feasible at the
EIC despite the relatively low jet transverse momentum and particle
multiplicities. We investigate the size of subleading power corrections
relevant at low energies within the Monte Carlo setup. In order to establish
the validity of the Monte Carlo tune, we also perform comparisons to jet shape
data at HERA. We further discuss detector requirements necessary for angularity
measurements at an EIC, focusing on hadron calorimeter energy and spatial
resolutions. Possible applications of precision jet substructure measurements
at the EIC include the tuning of Monte Carlo event generators, the extraction
of nonperturbative parameters and studies of cold nuclear matter effects. | hep-ph |
What the Tevatron Found?: The CDF collaboration has reported a 4.1\sigma\ excess in their lepton,
missing energy, and dijets channel. This excess, which takes the form of an
approximately Gaussian peak centered at a dijet invariant mass of 147 GeV, has
provoked a great deal of experimental and theoretical interest. Although the
D\O\ collaboration has reported that they do not observe a signal consistent
with CDF, there is currently no widely accepted explanation for the discrepancy
between these two experiments. A resolution of this issue is of great
importance---not least because it may teach us lessons relevant for future
searches at the LHC---and it will clearly require additional information. In
this paper, we consider the ability of the Tevatron and LHC detectors to
observe evidence associated with the CDF excess in a variety of channels. We
also discuss the ability of selected kinematic distributions to distinguish
between Standard Model explanations of the observed excess and various new
physics scenarios. | hep-ph |
Probing top-partners in Higgs + jets: Fermionic top-partners arise in models such as Composite Higgs and Little
Higgs. They modify Higgs properties, in particular how the Higgs couples to top
quarks. Alas, there is a low-energy cancellation acting in the coupling of the
Higgs boson to gluons and photons. As a result of this cancellation, no
information about the spectrum and couplings of the top-partners can be
obtained in gluon fusion to Higgs, just the overall new physics scale. In this
paper we show that this is not the case when hard radiation is taken into
account. Indeed, differential distributions in Higgs plus jets are sensitive to
the top-partner mass and coupling to the Higgs. We exploit the transverse
momentum distribution of the hard jet to obtain limits on the top-partners in
the 14 TeV LHC run, finding that 300 ifb of data of 14 TeV LHC are sufficient
to rule out top-sector mixing angles $\sin^2 (\theta_R)$ > 0.05 for
top-partners with masses from 300 GeV to above 2 TeV. | hep-ph |
Vortex Production in a First Order Phase-Transition at Finite
Temperature: We simulate the production of vortices in a first order phase transition at
finite temperature. The transition is carried out by randomly nucleating
critical bubbles and the effects of thermal fluctuations (which could be
relevant for vortex production) are represented by randomly nucleating
subcritical bubbles. Our results show that the presence of subcritical bubbles
suppresses vortices with clear and prominent profiles, though net number of
vortices is consistent with theoretical estimates. We also determine the
typical speed of vortices arising due to randomness associated with the phase
transition to be about 0.5. | hep-ph |
Confinement and complex singularities in QED3: The standard approximations of the Dyson--Schwinger equation lead to complex
singularities of the fermion propagator. In three-dimensional QED one can show
that this phenomenon might be related to confinement: a confining potential
leads to mass-like singularities at complex momenta, and thus to the absence of
a mass singularity on the real timelike axis. The correct treatment of the
vacuum polarization is essential for the confining nature of QED3. | hep-ph |
Radiative jet energy loss in a three-dimensional hydrodynamical medium
and high $p_T$ azimuthal asymmetry of $π_0$ suppression at mid and forward
rapidity at RHIC: The nuclear modification factor $R_{AA}$ for $\pi_0$ production in Au+Au
collisions at $\sqrt{s}=200$ AGeV is calculated, and studied at high transverse
momenta $p_T$. The soft thermalized nuclear medium is described within the
framework of relativistic ideal three-dimensional hydrodynamics. The energy
loss of partonic jets is evaluated in the context of gluon bremsstrahlung in
the thermalized partonic matter. We provide a systematic analysis of the
azimuthal asymmetry of $\pi_0$ suppression at high $p_T$ in central and
non-central collisions, at mid and forward rapidity. The determination of
$R_{AA}$ as a function of $p_T$, at different azimuthal angles, and different
rapidities makes for a stringent test of our theoretical understanding of jet
energy loss over a variety of in-medium path lengths, temperatures and initial
partonic jet energies. This lays the groundwork for a precise tomography of the
nuclear medium. | hep-ph |
Intrinsic three-body nuclear interaction from a constituent quark model: We study the short distance part of the intrinsic three-nucleon interaction
in a constituent quark model with color-spin interaction. For that purpose we
first calculate the transformation coefficient between the tribaryon
configuration and their corresponding three baryon basis. Using a formula for
the intrinsic three-body interaction in terms of a tribaryon configuration, we
find that after subtracting the corresponding two-baryon contributions, the
intrinsic three-body interaction vanishes in flavor SU(3) symmetric limit for
all quantum numbers for the three nucleon states. We further find that the
intrinsic three-body interaction also vanishes for flavor-spin type of quark
interaction. | hep-ph |
Direct detection of freeze-in inelastic dark matter: We show that the current sensitivities of direct detection experiments have
already reached the interesting parameter space of freeze-in dark matter models
if the dark sector is in the inelastic dark matter framework and the excited
dark matter state is cosmologically stable. Using results recently presented by
the XENON1T experiment, we present constraints on these models. We also show
that these models can explain the reported excess in the electron recoil
signals if the mass gap between the ground state and the excited state is at
keV scale. | hep-ph |
On the LHC sensitivity for non-thermalised hidden sectors: We show under rather general assumptions that hidden sectors that never reach
thermal equilibrium in the early Universe are also inaccessible for the LHC. In
other words, any particle that can be produced at the LHC must either have been
in thermal equilibrium with the Standard Model at some point or must be
produced via the decays of another hidden sector particle that has been in
thermal equilibrium. To reach this conclusion, we parametrise the cross section
connecting the Standard Model to the hidden sector in a very general way and
use methods from linear programming to calculate the largest possible number of
LHC events compatible with the requirement of non-thermalisation. We find that
even the HL-LHC cannot possibly produce more than a few events with energy
above 10 GeV involving states from a non-thermalised hidden sector. | hep-ph |
The effects of charmonium on the properties of the $1^{++}$ hidden charm
poles in effective field theory: In this study, the properties of the $J^{PC}=1^{++}$ hidden charm poles are
analyzed under the variation of the bare 2P charmonium mass within the
effective field theory proposed in Ref.[1]. The main focus of the current work
is on the pole trajectory of the $\chi_{c1}(2P)$ charmonium dressed by the $D
\bar{D}^*$ meson loops. It is shown that the trajectories of the pole change
radically for values of the bare charmonium mass above a certain value and also
depending on how close the pole is to the threshold. | hep-ph |
The Higgs portal and an unified model for dark energy and dark matter: We examine a scenario where the Higgs boson is coupled to an additional
singlet scalar field which we identify with a quintessence field. We show that
this results in an unified picture of dark matter and dark energy, where dark
energy is the zero-mode classical field rolling the usual quintessence
potential and the dark matter candidate is the quantum excitation (particle) of
the field, which is produced in the universe due to its coupling to the Higgs
boson. | hep-ph |
Opportunities in Neutrino Theory -- a Snowmass White Paper: Neutrino masses are clear evidence for physics beyond the standard model and
much more remains to be understood about the neutrino sector. We highlight some
of the outstanding questions and research opportunities in neutrino theory. We
show that most of these questions are directly connected to the very rich
experimental program currently being pursued (or at least under serious
consideration) in the United States and worldwide. Finally, we also comment on
the state of the theoretical neutrino physics community in the U.S. | hep-ph |
RECO level \sqrt{s}_{min} and subsystem \sqrt{s}_{min}: improved global
inclusive variables for measuring the new physics mass scale in missing
energy events at hadron colliders: The variable \sqrt{s}_{min} was originally proposed in arXiv:0812.1042 as a
model-independent, global and fully inclusive measure of the new physics mass
scale in missing energy events at hadron colliders. In the original incarnation
of \sqrt{s}_{min}, however, the connection to the new physics mass scale was
blurred by the effects of the underlying event, most notably initial state
radiation and multiple parton interactions. In this paper we advertize two
improved variants of the \sqrt{s}_{min} variable, which overcome this problem.
First we show that by evaluating the \sqrt{s}_{min} variable at the RECO level,
in terms of the reconstructed objects in the event, the effects from the
underlying event are significantly diminished and the nice correlation between
the peak in the \sqrt{s}_{min}^{(reco)} distribution and the new physics mass
scale is restored. Secondly, the underlying event problem can be avoided
altogether when the \sqrt{s}_{min} concept is applied to a subsystem of the
event which does not involve any QCD jets. We supply an analytic formula for
the resulting subsystem \sqrt{s}_{min}^{(sub)} variable and show that its peak
exhibits the usual correlation with the mass scale of the particles produced in
the subsystem. Finally, we contrast \sqrt{s}_{min} to other popular inclusive
variables such as H_T, M_{Tgen} and M_{TTgen}. We illustrate our discussion
with several examples from supersymmetry, and with dilepton events from top
quark pair production. | hep-ph |
Simulation of Beyond Standard Model Physics in Herwig++: We present a new approach for the simulation of Beyond Standard Model (BSM)
physics within the Herwig++ event generator. Our approach is more generic than
previous methods with the aim of minimising the effort of implementing further
new physics models. Spin correlations, which are important for BSM models due
to new heavy fermions and bosons, are discussed and their effects demonstrated
for the Minimal Supersymmetric Standard Model (MSSM) and Randall-Sundrum Model
using our new framework. | hep-ph |
Hard Photon Pair Production at LEP: The production of photon pairs in $e^+e^-\rightarrow f \bar f \gamma\gamma$
processes is studied using exact helicity amplitudes at tree level. Total cross
sections, including initial state radiation effects, are given. They are
presented in the case of quarks as a function of $y_{\rm cut}$ in the JADE
algorithm. In the case of leptons we use cuts similar to the ones employed in a
recent L3 analysis. Masses of the final state fermions are taken into account
when appropriate. The cross section $e^+e^-\rightarrow \tau^+ \tau^-
\gamma\gamma$ is about 10\% larger when the $\tau$ mass is neglected. We
obtain, with a different method, results which are in good agreement with L3
Montecarlo simulation. | hep-ph |
Nano-Hertz gravitational waves from collapsing domain walls associated
with freeze-in dark matter in light of pulsar timing array observations: Evidence for a stochastic gravitational wave background in the nHz frequency
band is recently reported by four pulsar timing array collaborations NANOGrav,
EPTA, CPTA, and PPTA. It can be interpreted by gravitational waves from
collapsing domain walls in the early universe. We assume such domain walls
arising from the spontaneous breaking of a $Z_2$ symmetry in a scalar field
theory, where a tiny $Z_2$-violating potential is required to make domain walls
unstable. We propose that this $Z_2$-violating potential is radiatively induced
by a feeble Yukawa coupling between the scalar field and a fermion field, which
is also responsible for dark matter production via the freeze-in mechanism.
Combining the pulsar timing array data and the observed dark matter relic
density, we find that the model parameters can be narrowed down to small
ranges. | hep-ph |
Direct Detection is testing Freeze-in: Dark Matter (DM) may belong to a hidden sector that is only feebly
interacting with the Standard Model (SM) and may have never been in thermal
equilibrium in the Early Universe. In this case, the observed abundance of dark
matter particles could have built up through a process known as Freeze-in. We
show that, for the first time, direct detection experiments are testing this DM
production mechanism. This applies to scenarios where the SM and hidden sectors
communicate through a light mediator particle of mass less than a few MeV.
Through the exchange of such light mediator, the very same FIMP candidates can
have self-interactions that are in the range required to address the small
scale structure issues of collisionless cold dark matter. | hep-ph |
Massive gluons and quarks and the equation of state obtained from SU(3)
lattice QCD: We analyze recent results of SU(3) lattice QCD calculations with a
phenomenological parametrization for the quark-gluon plasma equation of state
based on a quasi-particle picture with massive quarks and gluons. At high
temperature we obtain a good fit to the lattice data using perturbative thermal
quark and gluon masses from an improved HTL scheme. At temperatures close to
the confinement phase transition the fitted masses increase above the
perturbative value, and a non-zero (but small) bag constant is required to fit
the lattice data. | hep-ph |
Finite size source effects and the correlation of neutrino transition
probabilities through supernova turbulence: (Abridged) The transition probabilities describing the evolution of a
neutrino with a given energy along some ray through a turbulent supernova are
random variates unique to each ray. If the source of the neutrinos were a point
then all neutrinos of a given energy and emitted at the same time which were
detected in some far off location would have seen the same turbulent profile
therefore their transition probabilities would be exactly correlated. But if
the source has a finite size then the profiles seen by neutrinos emitted from
different points at the source will have seen different turbulence and the
correlation of the transition probabilities will be reduced. In this paper we
study the correlation of the neutrino transition probabilities through
turbulent supernova profiles as a function of the separation between the
emission points using an isotropic and an anisotropic power spectrum for the
random field used to model the turbulence. The spectral features in the high
density resonance mixing channel of the next Galactic supernova neutrino burst
may be strongly obscured by large amplitude turbulence when it enters the
signal due to the finite size of the source while the presence of features in
the low density and non resonant mixing channels may persist, the exact amount
depending upon the degree of anisotropy of the turbulence. | hep-ph |
Flavor-dependent U(3) Nambu Jona Lasinio coupling constant: A non-perturbative one gluon exchange quark-antiquark interaction is
considered to compute flavor dependent U(3) Nambu-Jona-Lasinio (NJL)-type
interaction of the form $G_{ij, \Gamma} (\bar{\psi} \lambda_i \Gamma \psi ) (
\bar{\psi} \lambda_j \Gamma \psi)$ for $i,j=0...8$ and $\Gamma=I, i \gamma_5$
from one loop polarization process with non degenerate u-d-s quark effective
masses. The resulting NJL-type coupling constants in all channels are resolved
in the long-wavelength limit and numerical results are presented for different
choices of an effective gluon propagator. Leading deviations with respect to a
flavor symmetric coupling constant are found to be of the order of
$(M_{f_2}^*-M_{f_1}^*)^n/(M_{f_2}^*+M_{f_1}^*)^n$, for $n=1,2$, where
$M_{f_i}^*$ are the effective masses of quarks $f_1,f_2=u, d$ and $s$. The
scalar channel coupling constants $G_{ij, s}$ can be considerably smaller than
pseudoscalar ones. The effect of the flavor-dependence of coupling constants
for the masses of pions and kaons may be nearly of the same order of magnitude
as the effect of the u,d and s quark mass non-degeneracy. The effect of these
coupling constants is also verified for some of the light scalar mesons masses,
usually described by quark-antiquark states, and for some observables of the
pseudoscalar mesons. | hep-ph |
Simulation of Proton and Iron Induced Extensive Air Showers: The reliable simulation of extensive air showers induced by different primary
particles (e. g. proton, iron, gamma etc.) is of great importance in high
energy cosmic ray research. The CORSIKA is a standard Monte-Carlo simulation
package to simulate the four dimensional evolution of Extensive Air Shower
(EAS) in the atmosphere initiated by gamma, hadrons and nuclei. CORSIKA has
different high energy interaction models like DPMJET, QGSJET, NEXUS, SIBYLL,
VENUS and EPOS which are based on different theoretical frameworks. The
influence of different hadronic interaction models, viz., QGSJET and DPMJET on
the lateral distribution functions (LDF) and muon to electron ratio of cosmic
ray EAS induced by 10^17 eV to 10^20 eV proton and iron primaries are explored
in this work. | hep-ph |
Probing Supersymmetric Dark Matter and the Electroweak Sector using
Vector Boson Fusion Processes: A Snowmass Whitepaper: Vector boson fusion (VBF) processes at the Large Hadron Collider (LHC)
provide a unique opportunity to search for new physics with electroweak
couplings. Two studies are presented: (i) A search of supersymmetric dark
matter in the final state of two VBF jets and large missing transverse energy
is presented at 14 TeV. Prospects for determining the dark matter relic density
are studied for the cases of Wino and Bino-Higgsino dark matter. The LHC could
probe Wino dark matter with mass up to approximately 600 GeV with a luminosity
of 1000 fb$^{-1}$. (ii) A search for the chargino/neutralino system in the
final state of two VBF jets, missing transverse energy and two $\tau$'s (light
stau case) and light lepton $e$ and $\mu$ (light slepton case). The $5 \sigma$
mass reach at 300 fb$^{-1}$ (1000 fb$^{-1}$) of LHC14 for inclusive and
opposite-sign $\tau$ pairs are 250 GeV (300 GeV) and 200 GeV (250 GeV),
respectively, for $\Delta M \, = \, m_{\tilde{\tau}_1} - m_{\neu{1}} \, = \,
30$ GeV. For $\Delta M \, = \, 15$ GeV, the $3 \sigma$ mass reach at 300
fb$^{-1}$ (1000 fb$^{-1}$) of LHC14 for inclusive $\tau$ pairs is 180 GeV. The
$5 \sigma$ mass reach at 300 fb$^{-1}$ (1000 fb$^{-1}$) of LHC14 for inclusive
and opposite-sign $\mu$ pairs are approximately 350 GeV (400 GeV) and 300 GeV
(350 GeV), respectively. The mass reaches in the same-sign final state cases
are similar to those in the opposite-sign cases. | hep-ph |
Matching to all orders and power corrections in heavy quark effective
theory: This talk reports on various aspects of the divergence of perturbative
expansions in the context of matching QCD onto heavy quark effective theory.
Implications for exclusive and inclusive decays of heavy mesons are discussed. | hep-ph |
Very High Energy Cosmic Rays from Centaurus A: Centaurus A is the nearest radio-loud AGN and is detected from radio to very
high energy gamma-rays. Its nuclear spectral energy distribution shows two
peaks, one in the far-infrared band and another at about 150 keV. By assuming
the second peak is due to the electron synchrotron emission and the power index
for the differential spectrum of the very high energy cosmic ray proton to be
2.7 we show that only pp interaction is responsible for the observed GeV-TeV
emission from Centaurus A. We also found that indeed many very high energy
cosmic ray protons from Centaurus A can arrive on Earth thus supporting the
recent observation of two events by Pierre Auger Observatory. | hep-ph |
Leptogenesis as an origin of dark matter and baryon asymmetries in the
E6 inspired SUSY models: We explore leptogenesis within the E6 inspired U(1) extension of the MSSM in
which exact custodial symmetry forbids tree-level flavour-changing transitions
and the most dangerous baryon and lepton number violating operators. This
supersymmetric (SUSY) model involves extra exotic matter beyond the MSSM. In
the simplest phenomenologically viable scenarios the lightest exotic fermions
are neutral and stable. These states should be substantially lighter than 1 eV
forming hot dark matter in the Universe. The low-energy effective Lagrangian of
the SUSY model under consideration possesses an approximate global U(1)_E
symmetry associated with the exotic states. The U(1)_E symmetry is explicitly
broken because of the interactions between the right-handed neutrino
superfields and exotic matter supermultiplets. As a consequence the decays of
the lightest right-handed neutrino/sneutrino give rise to both U(1)_E and
U(1)_{B-L} asymmetries. When all right-handed neutrino/sneutrino are relatively
light \sim 10^6-10^7 GeV the appropriate amount of the baryon asymmetry can be
induced via these decays if the Yukawa couplings of the lightest right-handed
neutrino superfields to the exotic matter supermultiplets vary between
10^{-4}-10^{-3}. | hep-ph |
Universality of traveling waves with QCD running coupling: ``Geometric scaling'', i.e. the dependence of DIS cross-sections on the ratio
Q/Q_S, where Q_S(Y) is the rapidity-dependent \saturation scale, can be
theoretically obtained from universal ``traveling wave'' solutions of the
nonlinear Balitsky-Kovchegov (BK) QCD evolution equation at fixed coupling. We
examine the similar mean-field predictions beyond leading-logarithmic order,
including running QCD coupling. | hep-ph |
Axial anomaly and vector meson dominance model: The dispersive representation of axial anomaly leads to the anomaly sum rules
(ASRs), exact nonperturbative relations in QCD. The analytical continuation of
the ASRs to the time-like region is performed. The transition form factors of
$\pi^0$, $\eta$ and $\eta'$ mesons in this region are calculated. A good
agreement with the available experimental data is found. Based on the ASRs, we
have provided the foundations for the vector meson dominance model in these
processes. | hep-ph |
Flavor-Changing Neutral Current Constraints in Topcolor-Assisted
Technicolor: It is argued that the topcolor models recently proposed by Hill [1] may face
significant constraints from flavor-changing neutral current processes (such as
$B-\bar{B}$ mixing) unless the mixing angles between down-type quarks are
small. The flavor-changing processes are mediated by scalar bound states which
are likely to be light as a result of the near critical dynamics of the
$b$-quark sector. The consequences of the latter on the bottom quark mass are
also briefly discussed. | hep-ph |
Exclusive diffractive processes in electron-ion collisions: We present a new technique to calculate the cross-section for diffractive
vector meson production and DVCS in electron-ion collisions based on the dipole
model. The measurement of these processes can provide valuable information on
non-linear QCD phenomena, such as gluon saturation, and is the the only known
way to gain insight into the spatial distribution of gluons in nuclei. We
present predictions of differential cross-section distribution $d\sigma/dQ^2$
and $d\sigma/dt$ for $J/\psi$ and $\phi$ meson production for diffractive
processes of heavy nuclei and demonstrate the feasibility of extracting the
gluon source distribution of heavy nuclei, F(b), from coherent diffraction. We
briefly introduce a new event generator based on our method that can be used
for studying exclusive diffractive processes at a future electron-ion collider. | hep-ph |
A Non-perturbative Treatment of Heavy Quarks and Mesons: A formalism for studying heavy quarks in terms of model Dyson-Schwinger
equations is developed. The formalism is the natural extension of a technique
which has proved successful in a number of studies of light hadron physics. The
dressed heavy quark propagator, calculated to leading order in the inverse
quark mass, is incorporated in a treatment of mesons consisting of a heavy
quark and light antiquark via the ladder approximation Bethe-Salpeter equation.
In the limit of infinite heavy quark mass the model is found to respect the
spectrum degeneracies present in Heavy Quark Effective Theory. An exploratory
numerical analysis of a simple form of the model is carried out to assess its
viability for studying $D$ and $B$ mesons. | hep-ph |
Electroweak Baryogenesis: Concrete in a SUSY Model with a Gauge Singlet: SUSY models with a gauge singlet easily allow for a strong first order
electroweak phase transition (EWPT) if the vevs of the singlet and Higgs fields
are of comparable size. We discuss the profile of the stationary expanding
bubble wall and CP-violation in the effective potential, in particular
transitional CP-violation inside the bubble wall during the EWPT. The
dispersion relations for charginos contain CP-violating terms in the WKB
approximation. These enter as source terms in the Boltzmann equations for the
(particle--antiparticle) chemical potentials and fuel the creation of a baryon
asymmetry through the weak sphaleron in the hot phase. This is worked out for
concrete parameters. | hep-ph |
The Y(2175) State in the QCD Sum Rule: We study the mass of the state Y(2175) of J^{PC} = 1^{--} in the QCD sum
rule. We construct both the diquark-antidiquark currents (ss)(s_bar s_bar) and
the meson-meson currents (s_bar s)(s_bar s). We find that there are two
independent currents for both cases, and derive the relations between them. The
OPE convergence of these two currents is sufficiently fast, which enables us to
perform good sum rule analysis. Both the SVZ sum rule and the finite energy sum
rule lead to a mass around 2.3+-0.4 GeV, which is consistent with the observed
mass within the uncertainties of the present QCD sum rule. The coupling of the
four-quark currents to lower lying states such as \phi(1020) turns out to be
rather small. We also discuss possible decay properties of Y(2175) if it is a
tetraquark state. | hep-ph |
Positronium energy levels at order $m α^7$: Product contributions
in the two-photon-annihilation channel: Ongoing improvements in the measurement of positronium transition intervals
motivate the calculation of the $O(m \alpha^7)$ corrections to these intervals.
In this work we focus on corrections to the spin-singlet parapositronium
energies involving virtual annihilation to two photons in an intermediate
state. We have evaluated all contributions to the positronium S-state energy
levels that can be written as the product of a one-loop correction on one side
of the annihilation event and another one-loop correction on the other side.
These effects contribute $\Delta E = -0.561971(25) m \alpha^7/\pi^3$ to the
parapositronium ground state energy. | hep-ph |
Calculation of fragmentation functions in two-hadron semi-inclusive
processes: We investigate the properties of interference fragmentation functions arising
from the emission of two leading hadrons inside the same jet for inclusive
lepton-nucleon deep-inelastic scattering. Using an extended spectator model for
the mechanism of the hadronization, we give a complete calculation and
numerical estimates for the examples of a proton-pion pair produced with
invariant mass on the Roper resonance, and of two pions produced with invariant
mass close to the $\rho$ mass. We discuss azimuthal angular dependence of the
leading order cross section to point up favourable conditions for extracting
transversity from experimental data. | hep-ph |
Natural Suppression of Proton Decay in Supersymmetric Type III Seesaw
Models: Supersymmetric standard model (MSSM) has two sources of rapid proton decay:
(i) R-parity breaking terms and (ii) higher dimensional Planck induced
B-violating terms; its extensions to include neutrino masses via the type I
seesaw mechanism need not have the first of these problems due to the existence
of B-L as a gauge symmetry but for sure always have the second one. If instead,
neutrino masses are explained in a type III seesaw extension of the standard
model, an anomaly free gauge symmetry different from B-L is known to exist. In
this note, it is shown that a realistic supersymmetric versions of this model
can be constructed (MSSM as well as SUSY left-right with type III seesaw) which
forbid the R-parity violating couplings of MSSM and suppress Planck scale
contributions to proton decay. The degree of suppression of the latter depends
on the weak gauge group. For the left-right case, the suppression to the
desired level is easily achieved. | hep-ph |
Combined constraints on the SUSY parameter space from $Δr$ ~and
Higgs boson search: Combining the constraints coming from the ~$M_W$ ~measurements and the
unsuccesful search for the Higgs boson at LEP we determine in the framework of
MSSM the allowed mass regions for the lighter scalar partner of the top quark.
For a heavy top quark particularily strong bounds are obtained for low values
of ~$\tan\beta\equiv v_2/v_1$ ~and light bottom squark. | hep-ph |
VISH$ν$: a unified solution to five SM shortcomings with a protected
electroweak scale: We propose a Standard Model extension, coined VISH$\nu$ (Variant-axIon Seesaw
Higgs $\nu$-trino), that is an $N_{\text{DW}} = 1$ variation of its
predecessor, the $\nu$DFSZ model. In accounting for the origin of neutrino
masses, dark matter and the baryon asymmetry of the universe, VISH$\nu$
inherits the explanatory power of $\nu$DFSZ while, of course, resolving the
strong $CP$ problem. In both models, the electroweak scale is naturally
protected from a high seesaw scale that is identified with the Peccei-Quinn
(PQ) spontaneous symmetry breaking scale. Through a flavour variant coupling
structure, VISH$\nu$ evades a domain wall problem, extending the cosmological
reach of the $\nu$DFSZ to include a viable period of inflation. The primary
focus of this paper is on the inflationary dynamics of VISH$\nu$ and their
naturalness in the sense of radiative stability. We find that non-minimal
gravitational couplings, generically developed by the VISH$\nu$ scalar fields,
naturally support a viable inflaton field which typically has both a PQ scalar
and Higgs component. An axion mass window [$40\mu\text{eV}, \sim 2\text{meV}$]
accessible to forthcoming searches, results for the case where PQ symmetry is
restored during the (p)reheating phase. | hep-ph |
$V_{cb}$ from the semileptonic decay $B\to D \ell \barν_{\ell}$ and
the properties of the $D$ meson distribution amplitude: The improved QCD light-cone sum rule (LCSR) provides an effective way to deal
with the heavy-to-light transition form factors (TFFs). Firstly, we adopt the
improved LCSR approach to deal with the $B\to D$ TFF $f^{+}(q^2)$ up to twist-4
accuracy. Due to the elimination of the most uncertain twist-3 contribution and
the large suppression of the twist-4 contribution, the obtained LCSR shall
provide us a good platform for testing the $D$-meson leading-twist DA. For the
purpose, we suggest a new model for the $D$-meson leading-twist DA
($\phi_{3D}$), whose longitudinal behavior is dominantly determined by a
parameter $B$. Moreover, we find its second Gegenbauer moment $a^D_2\sim B$.
Varying $B$ within certain region, one can conveniently mimic the $D$-meson DA
behavior suggested in the literature. Inversely, by comparing the estimations
with the experimental data on the $D$-meson involved processes, one can get a
possible range for the parameter $B$ and a determined behavior for the
$D$-meson DA. Secondly, we discuss the $B\to D$ TFF at the maximum recoil
region and present a detailed comparison of it with the pQCD estimation and the
experimental measurements. Thirdly, by applying the LCSR on $f^{+}(q^2)$, we
study the CKM matrix element $\Vcb$ together with its uncertainties by adopting
two types of processes, i.e. the $B^0/\bar{B}^0$-type and the $B^{\pm}$-type.
It is noted that a smaller $B \precsim 0.20$ shows a better agreement with the
experimental value on $\Vcb$. For example, for the case of $B=0.00$, we obtain
$|V_{cb}|(B^0/\bar{B}^0-{\rm type})=(41.28 {^{+5.68}_{-4.82}}
{^{+1.13}_{-1.16}}) \times 10^{-3}$ and $|V_{cb}|(B^{\pm}-{\rm type})=(40.44
{^{+5.56}_{-4.72}} {^{+0.98}_{-1.00}}) \times 10^{-3}$, whose first (second)
uncertainty comes from the squared average of the mentioned theoretical
(experimental) uncertainties. | hep-ph |
Properties of the Quark Gluon Plasma: A lattice perspective: We discuss results from lattice calculations for a few observables that are
sensitive to different length scales in the high temperature phase of QCD and
can give insight into its non-perturbative structure. We compare lattice
results with perturbative calculations at high temperature obtained for
vanishing and non-vanishing quark chemical potential. | hep-ph |
Single Top Production as a Probe of Heavy Resonances: The single top quark final state provides sensitivity to new heavy resonances
produced in proton-proton collisions at the Large Hadron Collider.
Particularly, the single top plus quark final state appears in models with
heavy charged bosons or scalars, or in models with flavor-changing neutral
currents involving the top quark. The cross sections and final state kinematics
distinguish such models from each other and from standard model backgrounds.
Several models of resonances decaying to a single top quark final state are
presented and their phenomenology is discussed. | hep-ph |
Monte-Carlo simulation of lepton pair production in "p pbar --> l+l- +
X" events at E_beam = 14 GeV: The lepton pair production in collisions of antiproton beam (E_beam = 14 GeV)
with proton target is studied on the basis of event samples simulated with
PYTHIA6 generator. Two types of quark level subprocesses are considered. The
first one goes through the production of virtual photon which converts into
lepton pair (q qbar --> gamma* --> l+l-) having a continuous energy spectrum of
the final lepton pair invariant mass. The other subprocess proceeds through the
J/Psi resonance production (p pbar --> J/Psi + X --> l+l- + X) with the
following decay of J/Psi into a pair of leptons. The distributions of different
kinematical variables which may be useful for the design of the muon system and
the electromagnetic calorimeter of the detector of PANDA experiment at FAIR are
presented. The analysis of these distribution shows the possibility to measure
the proton structure function in a new kinematical region defined by the
time-like values of the square of the momentum transferred 1 < Q^2 < 6.25 GeV^2
and withing a rather wide interval 0.05 < x < 0.7 of Bjorken x-variable. The
problems due to the presence of fake leptons that appear from meson decays, as
well as due to the background caused by minimum bias events and other QCD
processes, are also discussed. The set of cuts which allows one to separate the
signal events with lepton pairs from this kind of background events is
proposed. | hep-ph |
Precision Electroweak Physics at Future Collider Experiments: We present an overview of the present status and prospects for progress in
electroweak measurements at future collider experiments leading to precision
tests of the Standard Model of Electroweak Interactions. Special attention is
paid to the measurement of the W mass, the effective weak mixing angle, and the
determination of the top quark mass. Their constraints on the Higgs boson mass
are discussed. | hep-ph |
CP-Violation in b \to s \ell^{+} \ell^{-} transition Beyond the Standard
Model: In this study the CP-asymmetry in the b \to s \ell^{+} \ell^{-} transition
was investigated in minimal extension of the Standard Model where C_{9}^{eff}
receives an extra weak phase due to the new physics effects. We observed that
CP-Violation asymmetry can be measurable in the framework of scenario mentioned
above. | hep-ph |
LHC signals for neutrino mass model in bilinear R-parity violating mAMSB: We investigate a neutrino mass model in which the neutrino data is accounted
for by bilinear R-parity violating supersymmetry with anomaly mediated
supersymmetry breaking. We focus on the CERN Large Hadron Collider (LHC)
phenomenology, studying the reach of generic supersymmetry search channels with
leptons, missing energy and jets. A special feature of this model is the
existence of long lived neutralinos and charginos which decay inside the
detector leading to detached vertices. We demonstrate that the largest reach is
obtained in the displaced vertices channel and that practically all of the
reasonable parameter space will be covered with an integrated luminosity of 10
fb-1. We also compare the displaced vertex reaches of the LHC and Tevatron. | hep-ph |
Direct CP Violation in D -> hh Decays: Evidence of CP violation in the charm sector has been observed recently by
the LHCb and CDF Collaborations. The issue of whether it can be accommodated
within the standard model (SM) is examined in this talk. We conclude that the
CP asymmetry difference $\Delta a_{CP}^{\rm dir}$ between $D^0 \to K^+ K^-$ and
$D^0 \to \pi^+ \pi^-$ is of order $-(0.14\sim 0.15)%$. If the improved
theoretical estimate of $\Delta a_{CP}^{\rm dir}$ in the SM remains to be a few
per mille and the experimental measurement continues to be large with more
statistics in the future, it will be clear evidence of physics beyond the SM in
the charm sector. | hep-ph |
Nonexistence of the Longitudinal Polarisation of a Massive Gauge Bosons: This paper has been withdrawn by the authors due to some errors. | hep-ph |
Landau-Zener problem in a three-level neutrino system with non-linear
time dependence: We consider the level-crossing problem in a three-level system with
non-linearly time-varying Hamiltonian (time-dependence $t^{-3}$). We study the
validity of the so-called independent crossing approximation in the
Landau-Zener model by making comparison with results obtained numerically in
density matrix approach. We also demonstrate the failure of the so-called
"nearest zero" approximation of the Landau-Zener level-crossing probability
integral. | hep-ph |
Non-relativistic bound states at finite temperature (I): the hydrogen
atom: We illustrate how to apply modern effective field theory techniques and
dimensional regularization to factorize the various scales which appear in
non-relativistic bound states at finite temperature. We focus here on the
simplest case: the hydrogen atom. We discuss in detail the interplay of the
hard, soft and ultrasoft scales of the non-relativistic system at zero
temperature with the additional scales induced at finite temperature. We also
comment on the implications of our results for heavy quarkonium bound states in
the quark gluon plasma. | hep-ph |
QCD Saturation and Deuteron-Nucleus Collisions: We make quantitative predictions for the rapidity and centrality dependencies
of hadron multiplicities in dA collisions at RHIC basing on the ideas of parton
saturation in the Color Glass Condensate. | hep-ph |
Could the excess seen at 124-126 GeV be due to the Randall-Sundrum
Radion?: Current Higgs boson searches in various channels at the LHC point to an
excess at around 124-126 GeV due to a possibly standard-model-like Higgs boson.
If one examines more closely the channels (\gamma\gamma, WW*, and ZZ*) that
have excess, this "Higgs boson" may be the Randall-Sundrum radion \phi. Because
of the trace anomaly the radion has stronger couplings to the photon and gluon
pairs. Thus, it will enhance the production rates into gg and \gamma\gamma
while those for WW*, ZZ* and b\bar b are reduced relative to their
standard-model values. We show that it can match well with the data from CMS
for m_\phi = 124 GeV and the required scale \Lambda_\phi ~ <\phi > is about
0.68 TeV. | hep-ph |
Investigation of next-to-leading effects in CCFM: The effect of formally next-to-leading contributions to the CCFM evolution
equation are discussed. | hep-ph |
Nonabelian dark matter models for 3.5 keV X-rays: A recent analysis of XXM-Newton data reveals the possible presence of an
X-ray line at approximately 3.55 keV, which is not readily explained by known
atomic transitions. Numerous models of eV-scale decaying dark matter have been
proposed to explain this signal. Here we explore models of multicomponent
nonabelian dark matter with typical mass ~ 1-10 GeV (higher values being
allowed in some models) and eV-scale splittings that arise naturally from the
breaking of the nonabelian gauge symmetry. Kinetic mixing between the photon
and the hidden sector gauge bosons can occur through a dimension-5 or 6
operator. Radiative decays of the excited states proceed through transition
magnetic moments that appear at one loop. The decaying excited states can
either be primordial or else produced by upscattering of the lighter dark
matter states. These models are significantly constrained by direct dark matter
searches or cosmic microwave background distortions, and are potentially
testable in fixed target experiments that search for hidden photons. We note
that the upscattering mechanism could be distinguished from decays in future
observations if sources with different dark matter velocity dispersions seem to
require different values of the scattering cross section to match the observed
line strengths. | hep-ph |
Two-Photon Exchange in Electron-Proton Elastic Scattering: Theory Update: Recent theoretical developments in the studies of two-photon exchange effects
in elastic electron-proton scattering are reviewed. Two-photon exchange
mechanism is considered a likely source of discrepancy between polarized and
unpolarized experimental measurements of the proton electric form factor at
momentum transfers of several GeV$^2$. This mechanism predicts measurable
effects that are currently studied experimentally. | hep-ph |
NMSSM in gauge-mediated SUSY breaking without domain wall problem: A problem of the gauge-mediated SUSY breaking model is its difficulty to
generate a natural value of mu/Bmu, while the NMSSM is a natural framework to
solve the mu/Bmu problem. The NMSSM in gauge-mediated SUSY breaking in its
original form does not work well since the singlet field cannot develop a
desired vacuum expectation value. It also suffers from the cosmological domain
wall problem. We study an extension of the model to include additional
vector-like matter, which is charged under the hidden QCD. It is shown that
this simple extension solves both the problems. We study phenomenological and
cosmological implications of this extended models. The lightest Higgs mass can
be as large as 130-140 GeV for some model points. | hep-ph |
Reconstructing CMSSM parameters at the LHC with $\sqrt{s}=14$ TeV via
the golden decay channel: We identify a benchmark point in the CMSSM's heavy stau-coannihilation
region, which is favored by experiments, and demonstrate that it could be
accessible to the LHC at $\sqrt{s}=14$ TeV with 300/fb of integrated luminosity
via a golden decay measurement. With Monte-Carlo, we simulate sparticle
production and subsequent golden decay at the event level and perform
pseudo-measurements of sparticle masses from kinematic endpoints in invariant
mass distributions. We find that two lightest neutralino masses and the first
and second generation left-handed slepton and squark masses could be rather
precisely measured with correlated uncertainties. We investigate whether from
such measurements one could determine the CMSSM's Lagrangian parameters by
including a likelihood from our pseudo-measurements of sparticle masses in a
Bayesian analysis of the CMSSM's parameter space. We find that the CMSSM's
parameters can be accurately determined, with the exception of the common
trilinear parameter. Experimental measurements of the relic density by Planck
and the Higgs boson's mass slightly improve this determination, especially for
the common trilinear parameter. Finally, within our benchmark scenario, we show
that the neutralino dark matter will be accessible to direct searches in future
one tonne detectors. | hep-ph |
Phenomenology of Hidden Valleys at Hadron Colliders: We study the phenomenology of, and search techniques for, a class of "Hidden
Valleys." These models are characterized by low mass (well below a TeV) bound
states resulting from a confining gauge interaction in a hidden sector; the
states include a spin-one resonance that can decay to lepton pairs. Assuming
that the hidden sector communicates to the Standard Model (SM) through TeV
suppressed operators, taking into account the constraint from the $Z$ pole
physics at LEP, searches at Tevatron may be difficult in the particular class
of Hidden Valleys we consider, so that we concentrate on the searches at the
LHC. Hidden Valley events are characterized by high multiplicities of jets and
leptons in the final state. Depending on the scale of confinement in the hidden
sector, the events are typically more spherical, with lower thrust and higher
incidences of isolated leptons, than those from the SM background processes.
Most notably, high cluster invariant mass and very narrow, low mass resonances
in lepton pairs are the key observables to identify the signal. We use these
characteristics to develop a set of cuts to separate the Hidden Valley from SM,
and show that with these cuts LHC has a significant reach in the parameter
space. Our strategies are quite general and should apply well beyond the
particular class of models studied here. | hep-ph |
Suppression of Bremsstrahlung at Non-Zero Temperature: The first-order bremsstrahlung emission spectrum is $\alpha d\omega/\omega$
at zero temperature. If the radiation is emitted into a region that contains a
thermal distribution of photons, then the rate is increased by a factor
$1+N(\omega)$ where $N(\omega)$ is the Bose-Einstein function. The stimulated
emission changes the spectrum to $\alpha Td\omega/\omega^{2}$ for $\omega\ll
T$. If this were correct, an infinite amount of energy would be radiated in the
low frequency modes. This unphysical result indicates a breakdown of
perturbation theory. The paper computes the bremsstrahlung rate to all orders
of perturbation theory, neglecting the recoil of the charged particle. When the
perturbation series is summed, it has a different low-energy behavior. For
$\omega\ll\alpha T$, the spectrum is independent of $\omega$ and has a value
proportional to $d\omega/\alpha T$ . | hep-ph |
Charmonium decay in the C3P0 Model: In this work, we use the $C^3P_{\,0}$ model to calculate the decay widths of
the low lying charmonium $J^{PC}=1^{--}$ states, nominally $J/\psi(1S)$ and
$\psi(2S)$, in the following common channels: $\rho\,\pi$, $\omega\,\eta$,
$\omega\,\eta^\prime$, $K^{\ast +}\,K^-$, $K^{\ast 0}\,\bar{K}^0$,
$\phi\,\eta$, $\phi\,\eta^\prime$. | hep-ph |
Probing Planck Scale Spacetime By Cavity Opto-Atomic $^{87}$Rb
Interferometry: The project of \emph{"quantum spacetime phenomenology"} focuses on searching
pragmatically for the Planck scale quantum features of spacetime. Among these
features is the existence of a characteristic length scale addressed commonly
by effective approaches to quantum gravity (QG). This characteristic length
scale could be realized, for instance and simply, by generalizing the standard
Heisenberg uncertainty principle (HUP) to a \emph{"generalized uncertainty
principle"} (GUP). While usually it is expected that phenomena belonging to the
realm of QG are essentially probable solely at the so-called Planck energy,
here we show how a GUP proposal containing the most general modification of
coordinate representation of the momentum operator could be probed by a
\emph{"cold atomic ensemble recoil experiment"} (CARE) as a low energy quantum
system. This proposed atomic interferometer setup has advantages over the
conventional architectures owing to the enclosure in a high finesse optical
cavity which is supported by a new class of low power consumption integrated
devices known as \emph{"micro-electro-opto-mechanical systems"} (MEOMS). The
proposed system comprises of a micro mechanical oscillator instead of spherical
confocal mirrors as one of the components of high finesse optical cavity. In
the framework of a bottom-up QG phenomenological viewpoint and by taking into
account the measurement accuracy realized for the fine structure constant (FSC)
from the Rubidium ($^{87}$Rb) CARE, we set some constraints as upper bounds on
the characteristic parameters of the underlying GUP. In the case of
superposition of the possible GUP modification terms, we managed to set a tight
constraint as $0.999978<\lambda_0<1.00002$ for the dimensionless characteristic
parameter. | hep-ph |
Energetics of neutrinos in neutron stars: I review our proof that long range forces induced by the exchange of massless
neutrino-antineutrino pairs do not affect the stability of neutron stars. | hep-ph |
The description of $F_2$ at low $Q^2$: We analyse the data for the proton structure function $F_2$ over the entire
$Q^2$ domain, including especially low $Q^2$, in terms of perturbative and
non-perturbative QCD contributions. The small distance configurations are given
by perturbative QCD, while the large distance contributions are given by the
vector dominance model and, for the higher mass $q \bar{q}$ states, by the
additive quark approach. The interference between states of different
$q\bar{q}$ mass (in the perturbative contribution) is found to play a crucial
role in obtaining an excellent description of the data throughout the whole
$Q^2$ region, including photoproduction. | hep-ph |
Double transverse spin asymmetries in vector boson production: We investigate a helicity non-flip double transverse spin asymmetry in vector
boson production in hadron-hadron scattering, which was first considered by
Ralston and Soper at the tree level. It does not involve transversity functions
and in principle also arises in W-boson production for which we present the
expressions. The asymmetry requires observing the transverse momentum of the
vector boson, but it is not suppressed by explicit inverse powers of a large
energy scale. However, as we will show, inclusion of Sudakov factors causes
suppression of the asymmetry, which increases with energy. Moreover, the
asymmetry is shown to be approximately proportional to x_1 g_1(x_1) x_2 \bar
g_1(x_2), which gives rise to additional suppression at small values of the
light cone momentum fractions. This implies that it is negligible for Z or W
production and is mainly of interest for \gamma^* at low energies. We also
compare the asymmetry with other types of double transverse spin asymmetries
and discuss how to disentangle them. | hep-ph |
A Refined Analysis on the $X(3872)$ Resonance: We study the property of the $X(3872)$ meson by analyzing the $B\to K D\bar
D^*$ and $B\to K J/\psi \pi^+\pi^-$ decay processes. The competition between
the rescattering mediated through a Breit-Wigner resonance and the rescattering
generated from a local $D\bar{D}^* \to D\bar{D}^*$ interaction is carefully
studied through an effective lagrangian approach. Three different fits are
performed: pure Breit-Wigner case, pure $D\bar{D}^*$ molecule case with only
local rescattering vertices (generated by the loop chain), and the mixed case.
It is found that data supports the picture where X(3872) is mainly a ($\bar
cc$) Breit-Wigner resonance with a small contribution to the self-energy
generated by $\bar DD^*$ final state interaction. For our optimal fit, the pole
mass and width are found to be: $M_X=3871.2\pm0.7$MeV and
$\Gamma_X=6.5\pm1.2$MeV. | hep-ph |
Renormalization Group Improved Exponentiation of Soft Gluons in QCD: We extend the methods of Yennie, Frautschi and Suura to QCD for the summation
of soft gluon effects in which infrared singularities are cancelled to all
orders in $\alpha_s$. An explicit formula for the respective \rngp improved
exponentiated cross section is obtained for $q+\bbar{{q'}}\to q+\bbar{{q'}}+
n(G)$ at SSC energies. Possible applications are discussed. | hep-ph |
Heavy Quark Expansions for Inclusive Heavy-Flavour Decays and the
Lifetimes of Charm and Beauty Hadrons: Inclusive heavy-flavour decays can be described through $1/m_Q$ expansions
derived from QCD with the help of an operator product expansion. I sketch their
methodology and apply them first to semileptonic B decays; $|V(cb)|$ can be
extracted from $\Gamma _{SL}(B)$ and $\bar B \to l \nu D^*$ with the result:
$|V(cb)|_{incl} = 0.0413 \pm 0.0016_{exp} \pm 0.002_{theor}$, $|V(cb)|_{excl} =
0.0377 \pm 0.0016_{exp} \pm 0.002_{theor}$. The lifetimes of charm and beauty
hadrons are discussed. The charm lifetimes are predicted/reproduced as well as
could be expected. Predictions on B meson lifetimes agree with available data;
$\Lambda _b$ baryons are predicted to be shorter lived than B_d mesons by no
more than ~ 10% - in marked contrast to present measurements. I evaluate the
situation and comment on recent theoretical criticism. The importance of the
concepts of global vs. local quark-hadron duality is pointed out. | hep-ph |
Particle Spectra from the ALCOR Model: We introduce the Transchemistry Model as a dynamical extension of the
Algebraic Coalescence Rehadronization (ALCOR) model in describing the
hadronization of quark matter which is expected to be produced in relativistic
heavy ion collisions. Results are presented for CERN SPS NA49 Pb+Pb experiment
calculating hadron multiplicities and momentum spectra. The freeze-out
properties of different hadrons are characterized by similar temperature,
density and flow profiles in cylindrically symmetric geometry. | hep-ph |
Probe of anomalous neutrino couplings to W and Z in medium energy setup
of a beta-beam facility: Capability of medium energy setup of a beta beam experiment to probe new
physics contributions to neutrino-W and neutrino-Z couplings are investigated.
We employ the effective lagrangian approach of Buchmuller and Wyler and obtain
95% confidence level limits on neutrino couplings to these gauge bosons without
assuming the flavor universality of the coupling of neutrinos. We show that a
beta beam facility can place 3 to 20 times more restrictive limits than present
ones on the deviations from the electron neutrino couplings in the Standard
Model. | hep-ph |
Azimuthal spin asymmetries in light-cone constituent quark models: We present results for all leading-twist azimuthal spin asymmetries in
semi-inclusive lepton-nucleon deep-inelastic scattering due to T-even
transverse-momentum dependent parton distribution functions on the basis of a
light-cone constituent quark model. Attention is paid to discuss the range of
applicability of the model, especially with regard to the scale dependence of
the observables and the transverse-momentum dependence of the distributions. We
find good agreement with available experimental data and present predictions to
be further tested by future CLAS, COMPASS and HERMES data. | hep-ph |
Non-factorizable corrections to W-pair production: In this paper we study the non-factorizable QED corrections to
W-pair-mediated (charged-current) four-fermion production in electron-positron
collisions. A brief account of the obtained analytical results is given. They
turn out to be different from the ones published in the literature. For the
first time numerical results are presented, in particular the effects on the W
line-shape. These effects are of the order of a per cent. Applying the same
methods to ZZ- or ZH-mediated four-fermion production, the non-factorizable
$O(\alpha)$ corrections to the Z or H line-shape vanish. | hep-ph |
Search for new physics with neutrinos at Radioactive Ion Beam facilities: We propose applications of Radioactive Ion Beam facilities to investigate
physics beyond the Standard Model. In particular, we focus on the possible
measurement of coherent neutrino-nucleus scattering and on a search for sterile
neutrinos, by means of a low energy beta-beam with a Lorentz boost factor
$\gamma \approx 1$. In the considered setup the collected radioactive ions are
sent inside a 4$\pi$ detector. For the first application we provide the number
of events associated with neutrino-nucleus coherent scattering, when the
detector is filled in with a noble liquid. For the sterile search we consider
that the spherical detector is filled in with a liquid scintillator, and that
the neutrino detection channel is inverse-beta decay. We provide the exclusion
curves for the sterile neutrino mixing parameters, based upon the 3+1
formalism, depending upon the achievable ion intensity. Our results are
obtained both from total rates, and including spectral information with binning
in energy and in distance. The proposed experiment represents a possible
alternative to clarify the current anomalies observed in neutrino experiments. | hep-ph |
Top condensation as a motivated explanation of the top forward-backward
asymmetry: Models of top condensation can provide both a compelling solution to the
hierarchy problem as well as an explanation of why the top-quark mass is large.
The spectrum of such models, in particular topcolor-assisted technicolor,
includes top-pions, top-rhos and the top-Higgs, all of which can easily have
large top-charm or top-up couplings. Large top-up couplings in particular would
lead to a top forward-backward asymmetry through $t$-channel exchange, easily
consistent with the Tevatron measurements. Intriguingly, there is destructive
interference between the top-mesons and the standard model which conspire to
make the overall top pair production rate consistent with the standard model.
The rate for same-sign top production is also small due to destructive
interference between the neutral top-pion and the top-Higgs. Flavor physics is
under control because new physics is mostly confined to the top quark. In this
way, top condensation can explain the asymmetry and be consistent with all
experimental bounds. There are many additional signatures of topcolor with
large tu mixing, such as top(s)+jet(s) events, in which a top and a jet
reconstruct a resonance mass, which make these models easily testable at the
LHC. | hep-ph |
Heavy-light meson's physics in Lattice QCD: The possibility of revealing new physics by studying the flavor sector of the
Standard Model strongly depends upon the accuracy that will be achieved in
(near) future lattice QCD calculations and, in particular, on heavy-light
meson's observables. In turn, handling with heavy-light mesons on the lattice
is a challenging problem, because of the presence of two largely separated
energy scales, and at present it is impossible to extract matrix elements
involving B mesons in external states without recurring to some approximation.
In this note I give a fast overview of some of the methods that have been
devised to handle such kind of problems, emphasizing those based on finite
volume techniques, and briefly discuss some recent results obtained by their
application. | hep-ph |
Feasibility of tau g-2 measurements in ultra-peripheral collisions of
heavy ions: The anomalous magnetic moment of the tau lepton, a_tau = (g_tau - 2)/2, is a
sensitive probe of new physics but is extremely difficult to measure precisely
in contrast to electron and muon moments. The best experimental limits were set
by the DELPHI collaboration more than 15 years ago in studies of the ditau
production in the e+e -> e+e+tau+tau process. Ultra-peripheral collisions
(UPCs) of heavy ions at the LHC may provide a unique opportunity to improve the
a_tau constraints in the studies of Pb+Pb -> Pb+Pb+tau+tau process. We review
recent proposals to study ditau production via semi-leptonic tau decays in
Pb-Pb UPC with the available ATLAS and CMS data and discuss the feasibility to
explore this process down to low transverse momenta of decay leptons with the
ALICE and LHCb experiments. | hep-ph |
Measuring the Top Yukawa Coupling at 100 TeV: We propose a measurement of the top Yukawa coupling at a 100 TeV hadron
collider, based on boosted Higgs and top decays. We find that the top Yukawa
coupling can be measured to 1%, with excellent handles for reducing systematic
and theoretical uncertainties, both from side bands and from
$t\bar{t}H/t\bar{t}Z$ ratios. | hep-ph |
Remark on approximation in the calculation of the primordial spectrum
generated during inflation: We re-examine approximations in the analytical calculation of the primordial
spectrum of cosmological perturbation produced during inflation. Taking two
inflation models (chaotic inflation and natural inflation) as examples, we
numerically verify the accuracy of these approximations. | hep-ph |
R-charge Kills Monopoles: Large charge density, unlike high temperature, may lead to nonrestoration of
global and gauge symmetries. Supersymmetric GUTs with the appealing scenario of
unification scale being generated dynamically naturally contain global
continuous $R$ symmetries. We point out that the presence of a large $R$ charge
in the early Universe can lead to GUT symmetry nonrestoration. This provides a
simple way out of the monopole problem. | hep-ph |
Forward proton scattering in association with muon pair production via
the photon fusion mechanism at the LHC: Dilepton production in proton-proton collision through $\gamma\gamma$-fusion
with one proton scattered elastically while the second produces a hadron jet is
considered. Semi-analytical formulas describing the cross section of a muon
pair production are presented. | hep-ph |
Electroweak phase transition via Dilaton in Two-Time Physics: The Two-time model (2T model) has six dimensions with two dimensions of time,
has a Dilaton particle that makes the symmetry breaking differently from the
Standard Model. Assuming a soft break of $SP(2,R)$ symmetry, the 2T extension
can give a suitable picture of the matter-antimatter asymmetry by the
Baryogenesis scenario. By reducing the 2T metric to the Minkowski metric (1T
metric) and using a new form of Dilaton potential, we consider the electroweak
phase transition picture in the 2T model with the Dilaton as a trigger. Our
analysis shows that Electroweak Phase Transition (EWPT) is a first-order phase
transition at the $200$ GeV scale, its strength is about $1 - 3.08$ and the
mass of Dilaton is in the interval $[345,625]$ GeV. Therefore, the 2T-model
indirectly suggests that extra-dimension can also be a source of EWPT. | hep-ph |
New algorithm to study the pseudo-Wigner solution of the quark gap
equation in the framework of the (2+1)-flavor NJL model: In this paper, we study the pseudo-Wigner solution of the quark gap equation
with a recently proposed algorithm in the framework of the (2+1)-flavor
Nambu-Jona-Lasinio (NJL) model. We find that for the current quark mass $m_{\rm
u,d}=5.5$ MeV and chemical potential $\mu<\mu_{\rm TCP}=272.5$ MeV, the Nambu
solution and the positive pseudo-Wigner solution obtained via this algorithm is
consistent with the physical solution obtained with the iterative method.
Furthermore, the algorithm we used can help to illustrate the evolution of the
solutions of the gap equation from the chiral limit to non-chiral limit and
gives a prediction where the crossover line is located in the phase diagram for
$\mu<272.5$ MeV. In addition, we also study the chiral susceptibilities as well
as the loss of solutions for different chemical potentials. | hep-ph |
FIESTA 3: cluster-parallelizable multiloop numerical calculations in
physical regions: The goal of this paper is to present a new major release of the program
FIESTA (Feynman Integral Evaluation by a Sector decomposiTion Approach). This
version presents features like cluster-parallelization, new asymptotic
expansion algorithms, calculations in physical regions, new
sector-decomposition strategies, as well as multiple speed, memory, and
stability improvements. | hep-ph |
Dynamically generated axial-vector meson resonance in the chiral
symmetry restored vacuum: We study the modification of the properties of the axial-vector meson,
dynamically generated through the unitarization procedure, in the vacuum where
the chiral symmetry is restored. This is accomplished by scaling the pion decay
constant as the chiral order parameter while keeping the other input parameters
fixed. We find that the mass and width of the axial-vector meson reduce to
those of the vector meson, as anticipated by the Weinberg sum rules. The
findings are consistent with the results of a recent QCD sum rule calculation,
wherein the chiral order parameter is expressed through chiral
symmetry-breaking four-quark operators, leading to the mass-squared difference
scaling in proportion to variations in the chiral order parameter. We calculate
the scaling behavior for the mass differences obtained from the unitarization
method using both the physical and massless pion masses. | hep-ph |
Mass effects in muon and semileptonic b -> c decays: Quantum chromodynamics (QCD) effects in the semileptonic decay b -> c l nu
are evaluated to the second order in the coupling constant, O(alpha_s^2), and
to several orders in the expansion in quark masses, m_c/m_b. Corrections are
calculated for the total decay rate as well as for the first two moments of the
lepton energy and the hadron system energy distributions. Applied to the muon
decay, they decrease its predicted rate by -0.43 ppm. | hep-ph |
Scale dependence of the q and T parameters of the Tsallis distribution
in the process of jet fragmentation: The dependence of the $q$ and $T$ parameters of the
Tsallis-distribution-shaped fragmentation function (FF) on the fragmentation
scale (found to be equal to the jet mass) is calculated via the resummation of
the branching process of jet fragmentation in the leading-log appriximation
(LLA) in the $\phi^3$ theory. Jet and hadron spectra in electron-positron
($e^+e^-$) annihilations with 2- and 3-jet final states are calculated using
virtual leading partons. It is found that jets, produced earlier in the
branching process, are more energetic, and the energy, angle and multiplicity
distributions of hadrons stemming from them are broader. It is also found that
replacing the LL resummation in the branching process by a single splitting
provides good approximation for the jet energy distribution in 2-jet events.
Furthermore, a micro-canonical statistical event generator is presented for the
event-by-event calculation of hadron momenta in $e^+e^-$ annihilations. | hep-ph |
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