13,538 research outputs found
Effects of the R-parity violation in the minimal supersymmetric standard model on dilepton pair production at the CERN LHC
We investigate in detail the effects of the R-parity lepton number violation
in the minimal supersymmetric standard model (MSSM) on the parent process at the CERN Large Hadron Collider (LHC). The numerical
comparisons between the contributions of the R-parity violating effects to the
parent process via the Drell-Yan subprocess and the gluon-gluon fusion are
made. We find that the R-violating effects on pair production at the
LHC could be significant. The results show that the cross section of the pair productions via gluon-gluon collision at the LHC can be of the order
of fb, and this subprocess maybe competitive with the production
mechanism via the Drell-Yan subprocess. We give also quantitatively the
analysis of the effects from both the mass of sneutrino and coupling strength
of the R-parity violating interactions.Comment: 18 pages, 10 figures, accepted by Phys. Rev.
Field Decomposition and the Ground State Structure of SU(2) Yang-Mills Theory
We compute the effective potential of SU(2) Yang-Mills theory using the
background field method and the Faddeev-Niemi decomposition of the gauge
fields. In particular, we find that the potential will depend on the values of
two scalar fields in the decomposition and that its structure will give rise to
a symmetry breaking.Comment: 8 pages, 1 figure. Typos corrected and title change
QED in external fields, a functional point of view
A functional partial differential equation is set for the proper graphs
generating functional of QED in external electromagnetic fields. This equation
leads to the evolution of the proper graphs with the external field amplitude
and the external field gauge dependence of the complete fermion propagator and
vertex is derived non-perturbativally.Comment: 8 pages, published versio
The influence of cosmological transitions on the evolution of density perturbations
We study the influence of the reheating and equality transitions on
superhorizon density perturbations and gravitational waves. Recent criticisms
of the `standard result' for large-scale perturbations in inflationary
cosmology are rectified. The claim that the `conservation law' for the
amplitude of superhorizon modes was empty is shown to be wrong. For sharp
transitions, i.e. the pressure jumps, we rederive the Deruelle-Mukhanov
junction conditions. For a smooth transition we correct a result obtained by
Grishchuk recently. We show that the junction conditions are not crucial,
because the pressure is continuous during the reheating transition. The problem
occurred, because the perturbed metric was not evolved correctly through the
smooth reheating transition. Finally, we derive the `standard result' within
Grishchuks's smooth (reheating) transition.Comment: New references and one appendix added, misprints corrected. To be
published in Phys. Rev. D. 29 pages, ReVTe
Prospects for joint radio telescope and gravitational wave searches for astrophysical transients
The radio skies remain mostly unobserved when it comes to transient
phenomena. The direct detection of gravitational waves will mark a major
milestone of modern astronomy, as an entirely new window will open on the
universe. Two apparently independent phenomena can be brought together in a
coincident effort that has the potential to boost both searches. In this paper
we will outline the scientific case that stands behind these future joint
observations and will describe the methods that might be used to conduct the
searches and analyze the data. The targeted sources are binary systems of
compact objects, known to be strong candidate sources for gravitational waves.
Detection of transients coincident in these two channels would be a significant
smoking gun for first direct detection of gravitational waves, and would open
up a new field for characterization of astrophysical transients involving
massive compact objects.Comment: 12 pages, Amaldi 8 Conference (New York, 2009) proceedings pape
Non-transversality of the gluon polarization tensor in a chromomagnetic background
We investigate the question about the transversality of the gluon
polarization tensor in a homogeneous chromomagnetic background field. We
re-derive the non transversality known from a pure one loop calculation using
the Slavnov-Taylor identities. In addition we generalize the procedure to
arbitrary gauge fixing parameter and calculate the -dependent part
of the polarization tensor.Comment: subm. to TM
Contribution of Long Wavelength Gravitational Waves to the CMB Anisotropy
We present an in depth discussion of the production of gravitational waves
from an inflationary phase that could have occurred in the early universe,
giving derivations for the resulting spectrum and energy density. We also
consider the large-scale anisotropy in the cosmic microwave background
radiation coming from these waves. Assuming that the observed quadrupole
anisotropy comes mostly from gravitational waves (consistent with the
predictions of a flat spectrum of scalar density perturbations and the measured
dipole anisotropy) we describe in detail how to derive a value for the scale of
inflation of GeV, which is at a particularly interesting
scale for particle physics. This upper limit corresponds to a 95\% confidence
level upper limit on the scale of inflation assuming only that the quadrupole
anisotropy from gravitational waves is not cancelled by another source. Direct
detection of gravitational waves produced by inflation near this scale will
have to wait for the next generation of detectors.Comment: (LaTeX 16 pages), 2 figures not included, YCTP-P16-9
Searches for Gravitational Waves from Binary Neutron Stars: A Review
A new generation of observatories is looking for gravitational waves. These
waves, emitted by highly relativistic systems, will open a new window for ob-
servation of the cosmos when they are detected. Among the most promising
sources of gravitational waves for these observatories are compact binaries in
the final min- utes before coalescence. In this article, we review in brief
interferometric searches for gravitational waves emitted by neutron star
binaries, including the theory, instru- mentation and methods. No detections
have been made to date. However, the best direct observational limits on
coalescence rates have been set, and instrumentation and analysis methods
continue to be refined toward the ultimate goal of defining the new field of
gravitational wave astronomy.Comment: 30 pages, 5 Figures, to appear in "Short-Period Binary Stars:
Observations, Analyses, and Results", Ed.s Eugene F. Milone, Denis A. Leahy,
David W. Hobil
Jet Energy Density in Hadron-Hadron Collisions at High Energies
The average particle multiplicity density dN/deta is the dynamical quantity
which reflects some regularities of particle production in low-pT range. The
quantity is an important ingredient of z-scaling. Experimental results on
charged particle density are available for pp, pA and AA collisions while
experimental properties of the jet density are still an open question. The goal
of this work is to find the variable which will reflect the main features of
the jet production in low transverse energy range and play the role of the
scale factor for the scaling function psi(z) and variable z in data
z-presentation. The appropriate candidate is the variable we called "scaled jet
energy density". Scaled jet energy density is the probability to have a jet
with defined ET in defined xT and pseudorapidity regions. The PYTHIA6.2 Monte
Carlo generator is used for calculation of scaled jet energy density in
proton-proton collisions over a high energy range (sqrt s = 200-14000 GeV) and
at eta = 0. The properties of the new variable are discussed and sensitivity to
"physical scenarios" applied in the standard Monte Carlo generator is noted.
The results of scaled jet energy density at LHC energies are presented and
compared with predictions based on z-scaling.Comment: 11 pages, LaTeX, 8 figures, Presented at the XVII International
Baldin Seminar on High Energy Physics Problems "Relativistic Nuclear Physics
& Quantum Chromodynamics", Dubna, Russia, September 27 - October 2, 200
Reheating and thermalization in a simple scalar model
We consider a simple model for the Universe reheating, which consists of a
single self--interacting scalar field in Minkowskian space--time. Making use of
the existence of an additional small parameter proportional to the amplitude of
the initial spatially homogeneous field oscillations, we show that the behavior
of the field can be found reliably. We describe the evolution of the system
from the homogeneous oscillations to the moment when thermalization is
completed. We compare our results with the Hartree--Fock approximation and
argue that some properties found for this model may be the common features of
realistic theories.Comment: Some changes in Introduction and Discussion, comparison with the
Hartree--Fock results added. 37 pages, 2 postscript figures attache
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