4,328 research outputs found
Real Time Nonequilibrium Dynamics of Quantum Plasmas. Quantum Kinetics and the Dynamical Renormalization Group
We implement the dynamical renormalization group (DRG) using the hard thermal
loop (HTL) approximation for the real-time nonequilibrium dynamics in hot
plasmas. The focus is on the study of the relaxation of gauge and fermionic
mean fields and on the quantum kinetics of the photon and fermion distribution
functions. As a concrete physical prediction, we find that for a QGP of
temperature T sim 200 MeV and lifetime 10 < t < 50 fm/c there is a new
contribution to the hard (k \sim T) photon production from off-shell
bremsstrahlung (q rightarrow q gamma and bar{q} rightarrow bar{q} gamma) at
just O (alpha) that grows logarithmically in time and is comparable to the
known on-shell Compton scattering and pair annihilation at O(alpha alpha_s).Comment: LaTex, 5 pages, one .ps figure, lecture given at the DPF 2000
Conference, August 9-12, Columbus, Ohi
The Effective Theory of Inflation and the Dark Matter Status in the Standard Model of the Universe
We present here the effective theory of inflation `a la Ginsburg-Landau in
which the inflaton potential is a polynomial. The slow-roll expansion becomes a
systematic 1/N expansion where N ~ 60. The spectral index and the ratio of
tensor/scalar fluctuations are n_s - 1 = O(1/N), r = O(1/N) while the running
turns to be d n_s/d \ln k = O(1/N^2) and can be neglected. The energy scale of
inflation M ~ 0.7 10^{16} GeV is completely determined by the amplitude of the
scalar adiabatic fluctuations. A complete analytic study plus the Monte Carlo
Markov Chains (MCMC) analysis of the available CMB+LSS data showed: (a) the
spontaneous breaking of the phi -> - phi symmetry of the inflaton potential.
(b) a lower bound for r: r > 0.023 (95% CL) and r > 0.046 (68% CL). (c) The
preferred inflation potential is a double well, even function of the field with
a moderate quartic coupling yielding as most probable values: n_s = 0.964, r =
0.051. This value for r is within reach of forthcoming CMB observations. We
investigate the DM properties using cosmological theory and the galaxy
observations. Our DM analysis is independent of the particle physics model for
DM and it is based on the DM phase-space density rho_{DM}/sigma^3_{DM}. We
derive explicit formulas for the DM particle mass m and for the number of
ultrarelativistic degrees of freedom g_d (hence the temperature) at decoupling.
We find that m turns to be at the keV scale. The keV scale DM is
non-relativistic during structure formation, reproduces the small and large
scale structure but it cannot be responsible of the e^+ and pbar excess in
cosmic rays which can be explained by astrophysical mechanisms (Abridged).Comment: 28 pages; to be published in the Lev Lipatov Festschrift on the
occasion of Lev's 70th birthday, `Subtleties in Quantum Field Theories', D.
Diakonov, Editor, Gatchina, Russia, 201
Strings Next To and Inside Black Holes
The string equations of motion and constraints are solved near the horizon
and near the singularity of a Schwarzschild black hole. In a conformal gauge
such that ( = worldsheet time coordinate) corresponds to the
horizon () or to the black hole singularity (), the string
coordinates express in power series in near the horizon and in power
series in around . We compute the string invariant size and
the string energy-momentum tensor. Near the horizon both are finite and
analytic. Near the black hole singularity, the string size, the string energy
and the transverse pressures (in the angular directions) tend to infinity as
. To leading order near , the string behaves as two dimensional
radiation. This two spatial dimensions are describing the sphere in the
Schwarzschild manifold.Comment: RevTex, 19 pages without figure
Strings Propagating in the 2+1 Dimensional Black Hole Anti de Sitter Spacetime
We study the string propagation in the 2+1 black hole anti de Sitter
background (2+1 BH-ADS). We find the first and second order fluctuations around
the string center of mass and obtain the expression for the string mass. The
string motion is stable, all fluctuations oscillate with real frequencies and
are bounded, even at We compare with the string motion in the ordinary
black hole anti de Sitter spacetime, and in the black string background, where
string instabilities develop and the fluctuations blow up at We find the
exact general solution for the circular string motion in all these backgrounds,
it is given closely and completely in terms of elliptic functions. For the
non-rotating black hole backgrounds the circular strings have a maximal bounded
size they contract and collapse into No indefinitely growing
strings, neither multi-string solutions are present in these backgrounds. In
rotating spacetimes, both the 2+1 BH-ADS and the ordinary Kerr-ADS, the
presence of angular momentum prevents the string from collapsing into
The circular string motion is also completely solved in the black hole de
Sitter spacetime and in the black string background (dual of the 2+1 BH-ADS
spacetime), in which expanding unbounded strings and multi-string solutions
appear.Comment: Latex, 54 pages + 2 tables and 4 figures (not included). PARIS-DEMIRM
94/01
String Propagation through a Big Crunch/Big Bang Transition
We consider the propagation of classical and quantum strings on cosmological
space-times which interpolate from a collapsing phase to an expanding phase. We
begin by considering the classical propagation of strings on space-times with
isotropic and anisotropic cosmological singularities. We find that cosmological
singularities fall into two classes, in the first class the string evolution is
well behaved all the way up to the singularity, whilst in the second class it
becomes ill-defined. Then assuming the singularities are regulated by string
scale corrections, we consider the implications of the propagation through a
`bounce'. It is known that as we evolve through a bounce, quantum strings will
become excited giving rise to `particle transmutation'. We reconsider this
effect, giving qualitative arguments for the amount of excitation for each
class. We find that strings whose physical wavelength at the bounce is less
that inevitably emerge in highly excited states, and that in
this regime there is an interesting correspondence between strings on
anisotropic cosmological space-times and plane waves. We argue that long
wavelength modes, such as those describing cosmological perturbations, will
also emerge in mildly excited string scale mass states. Finally we discuss the
relevance of this to the propagation of cosmological perturbations in models
such as the ekpyrotic/cyclic universe.Comment: 15 page
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