221 research outputs found
Out-of-equilibrium evolution of scalar fields in FRW cosmology: renormalization and numerical simulations
We present a renormalized computational framework for the evolution of a
self-interacting scalar field (inflaton) and its quantum fluctuations in an FRW
background geometry. We include a coupling of the field to the Ricci scalar
with a general coupling parameter . We take into account the classical and
quantum back reactions, i.e., we consider the the dynamical evolution of the
cosmic scale factor. We perform, in the one-loop and in the large-N
approximation, the renormalization of the equation of motion for the inflaton
field, and of its energy momentum tensor. Our formalism is based on a
perturbative expansion for the mode functions, and uses dimensional
regularization. The renormalization procedure is manifestly covariant and the
counter terms are independent of the initial state. Some shortcomings in the
renormalization of the energy-momentum tensor in an earlier publication are
corrected. We avoid the occurence of initial singularities by constructing a
suitable class of initial states. The formalism is implemented numerically and
we present some results for the evolution in the post-inflationary preheating
era.Comment: 44 pages, uses latexsym, 6 pages with 11 figures in a .ps fil
Turbulent Thermalization
We study, analytically and with lattice simulations, the decay of coherent
field oscillations and the subsequent thermalization of the resulting
stochastic classical wave-field. The problem of reheating of the Universe after
inflation constitutes our prime motivation and application of the results. We
identify three different stages of these processes. During the initial stage of
``parametric resonance'', only a small fraction of the initial inflaton energy
is transferred to fluctuations in the physically relevant case of sufficiently
large couplings. A major fraction is transfered in the prompt regime of driven
turbulence. The subsequent long stage of thermalization classifies as free
turbulence. During the turbulent stages, the evolution of particle distribution
functions is self-similar. We show that wave kinetic theory successfully
describes the late stages of our lattice calculation. Our analytical results
are general and give estimates of reheating time and temperature in terms of
coupling constants and initial inflaton amplitude.Comment: 27 pages, 13 figure
The effect of memory on relaxation in a scalar field theory
We derive a kinetic equation with a non-Markovian collision term which
includes a memory effect, from Kadanoff-Baym equations in theory
within the three-loop level for the two-particle irreducible (2PI) effective
action. The memory effect is incorporated into the kinetic equation by a
generalized Kadanoff-Baym ansatz.Based on the kinetic equations with and
without the memory effect, we investigate an influence of this effect on decay
of a single particle excitation with zero momentum in 3+1 dimensions and the
spatially homogeneous case. Numerical results show that, while the time
evolution of the zero mode is completely unaffected by the memory effect due to
a separation of scales in the weak coupling regime, this effect leads first to
faster relaxation than the case without it and then to slower relaxation as the
coupling constant increases.Comment: 12 pages, 6 eps figure
Neutral Higgs sector of the next-to-minimal supersymmetric standard model with explicit CP violation
The neutral Higgs sector of the next-to-minimal supersymmetric standard model
(NMSSM) with explicit CP violation is investigated at the 1-loop level, using
the effective potential method; not only the loops involving the third
generation of quarks and scalar quarks, but also the loops involving boson,
charged Higgs boson, and chargino are taken into account. It is found that for
some parameter values of the NMSSM the contributions from the boson,
charged Higgs boson, and chargino loops may modify the masses of the neutral
Higgs bosons and the mixings among them significantly, depending on the CP
phase. In collisions, the prospects for discovering neutral Higgs
bosons are investigated within the context of the NMSSM with explicit CP
violation when the dominant component of the lightest neutral Higgs boson is
the Higgs singlet field of the NMSSM.Comment: Latex, 23 pages, 6 figure
Origin of the energy bandgap in epitaxial graphene
We studied the effect of quantum confinement on the size of the band gap in
single layer epitaxial graphene. Samples with different graphene terrace sizes
are studied by using low energy electron microscopy (LEEM) and angle-resolved
photoemission spectroscopy (ARPES). The direct correlation between the terrace
size extracted from LEEM and the gap size extracted from ARPES shows that
quantum confinement alone cannot account for the large gap observed in
epitaxial graphene samples
Prevalence and antibiotic profile of Shiga-toxin producing Escherichia coli and Escherichia coli O157: H7 in beef and buffalo
Possibility of spontaneous CP violation in the nonminimal supersymmetric standard model with two neutral Higgs singlets
A supersymmetric standard model with two Higgs doublets and two Higgs
singlets is investigated if it can accommodate the possibility of spontaneous
CP violation. Assuming the degeneracy of the scalar quark masses of the third
generation, we find that spontaneous CP violation in the Higgs sector is viable
in our model. In the case of spontaneous CP violation, the masses of the
lightest two neutral Higgs bosons are estimated to be 80 and 125 GeV for some
parameter values in our model, which, are consistent with LEP2 data.Comment: 18 pages, 3figure
Charged Higgs boson in the next-to-minimal supersymmetric standard model with explicit CP violation
The phenomenology of the explicit CP violation in the Higgs sector of the
next-to-minimal supersymmetric standard model (NMSSM) is investigated, with
emphasis on the charged Higgs boson. The radiative corrections due to both
quarks and scalar-quarks of the third generation are taken into account, and
the negative result of the search for the Higgs bosons at CERN LEP2, with the
discovery limit of 0.1 pb, is imposed as a constraint. It is found that there
are parameter regions of the NMSSM where the lightest neutral Higgs boson may
even be massless, without being detected at LEP2. This implies that the LEP2
data do not contradict the existence of a massless neutral Higgs boson in the
NMSSM. For the charged Higgs boson, the radiative corrections to its mass may
be negative in some parameter regions of the NMSSM. The phenomenological lower
bound on the radiatively corrected mass of the charged Higgs boson is increased
as the CP violation becomes maximal, i.e., as the CP violating phase becomes
. At the maximal CP violation, its lower bound is about 110 GeV for 5
40. The vacuum expectation value (VEV) of the
neutral Higgs singlet is shown to be no smaller than 16 GeV for any parameter
values of the NMSSM with explicit CP violation. This value of the lower limit
is found to increase up to about 45 GeV as the ratio () of the VEVs
of the two Higgs doublets decreases to smaller values ( 2). The discovery
limit of the Higgs boson search at LEP2 is found to cover about a half of the
kinematically allowed part of the whole parameter space of the NMSSM, and the
portion is roughly stable against the CP violating phase.Comment: Latex, 24 pages, 6 figure
Static coupling effect of a two-degree-of-freedom direct drive induction motor
Two-degree-of-freedom motors are capable of producing linear, rotary, and helical motion, and thus have widespread applications in special industries. In this study, a new concept- static coupling effect is studied in the two-degree-of-freedom direct-drive induction motor (2DoFDDIM). The proposed approach is based on the image method and the three-dimensional (3D) finite-element method. The image method model is established to analyse its reasons and predict the main effects, which are then verified by the proposed 3D finite-element static coupling model and experiments. The induced voltages and currents are produced in the static part and induced torque or force is obtained, even though the static part is not energised. It is concluded that the static coupling effect increases with the supply frequency and is influenced by the stator winding configuration. Thus, the existence of the static coupling effect is confirmed, which must be taken into account in future optimisation and precise control of the 2DoFDDIM
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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