69 research outputs found
Correlations and Equilibration in Relativistic Quantum Systems
In this article we study the time evolution of an interacting field
theoretical system, i.e. \phi^4-field theory in 2+1 space-time dimensions, on
the basis of the Kadanoff-Baym equations for a spatially homogeneous system
including the self-consistent tadpole and sunset self-energies. We find that
equilibration is achieved only by inclusion of the sunset self-energy.
Simultaneously, the time evolution of the scalar particle spectral function is
studied for various initial states. We also compare associated solutions of the
corresponding Boltzmann equation to the full Kadanoff-Baym theory. This
comparison shows that a consistent inclusion of the spectral function has a
significant impact on the equilibration rates only if the width of the spectral
function becomes larger than 1/3 of the particle mass. Furthermore, based on
these findings, the conventional transport of particles in the on-shell
quasiparticle limit is extended to particles of finite life time by means of a
dynamical spectral function A(X,\vec{p},M^2). The off-shell propagation is
implemented in the Hadron-String-Dynamics (HSD) transport code and applied to
the dynamics of nucleus-nucleus collisions.Comment: 20 pages, 7 figures to appear in "Nonequilibrium at short time scales
- Formation of correlations", edited by K. Morawetz, Springer, Berlin (2003),
p16
Primordial Black Holes: sirens of the early Universe
Primordial Black Holes (PBHs) are, typically light, black holes which can
form in the early Universe. There are a number of formation mechanisms,
including the collapse of large density perturbations, cosmic string loops and
bubble collisions. The number of PBHs formed is tightly constrained by the
consequences of their evaporation and their lensing and dynamical effects.
Therefore PBHs are a powerful probe of the physics of the early Universe, in
particular models of inflation. They are also a potential cold dark matter
candidate.Comment: 21 pages. To be published in "Quantum Aspects of Black Holes", ed. X.
Calmet (Springer, 2014
Isgur-Wise function in a QCD inspired potential model with confinement as parent in the Variationally Improved Perturbation Theory (VIPT)
We have recently reported the calculation of slope and curvature of
Isgur-Wise function based on Variationally Improved Perturbation Theory (VIPT)
in a QCD inspired potential model. In that work, Coulombic potential was taken
as the parent while the linear one as the perturbation.In this work, we choose
the linear one as the parent with Coulombic one as the perturbation and see the
consequences. Keywords: VIPT,Isgur-Wise function, charge radii and convexity
pa- rameter
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Vacuum Topology of the Two Higgs Doublet Model
We perform a systematic study of generic accidental Higgs-family and CP
symmetries that could occur in the two-Higgs-doublet-model potential, based on
a Majorana scalar-field formalism which realizes a subgroup of GL(8,C). We
derive the general conditions of convexity and stability of the scalar
potential and present analytical solutions for two non-zero neutral vacuum
expectation values of the Higgs doublets for a typical set of six symmetries,
in terms of the gauge-invariant parameters of the theory. By means of a
homotopy-group analysis, we identify the topological defects associated with
the spontaneous symmetry breaking of each symmetry, as well as the massless
Goldstone bosons emerging from the breaking of the continuous symmetries. We
find the existence of domain walls from the breaking of Z_2, CP1 and CP2
discrete symmetries, vortices in models with broken U(1)_PQ and CP3 symmetries
and a global monopole in the SO(3)_HF-broken model. The spatial profile of the
topological defect solutions is studied in detail, as functions of the
potential parameters of the two-Higgs doublet model. The application of our
Majorana scalar-field formalism in studying more general scalar potentials that
are not constrained by the U(1)_Y hypercharge symmetry is discussed. In
particular, the same formalism may be used to properly identify seven
additional symmetries that may take place in a U(1)_Y-invariant scalar
potential.Comment: 89 pages, 13 tables and 12 figures (version as to appear in JHEP
Laser Interactions for the Synthesis and In Situ Diagnostics of Nanomaterials
Laser interactions have traditionall been at thec center of nanomaterials science, providing highly nonequilibrium growth conditions to enable the syn- thesis of novel new nanoparticles, nanotubes, and nanowires with metastable phases. Simultaneously, lasers provide unique opportunities for the remote char- acterization of nanomaterial size, structure, and composition through tunable laser spectroscopy, scattering, and imaging. Pulsed lasers offer the opportunity, there- fore, to supply the required energy and excitation to both control and understand the growth processes of nanomaterials, providing valuable views of the typically nonequilibrium growth kinetics and intermediates involved. Here we illustrate the key challenges and progress in laser interactions for the synthesis and in situ diagnostics of nanomaterials through recent examples involving primarily carbon nanomaterials, including the pulsed growth of carbon nanotubes and graphene
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