682 research outputs found
Primordial Entropy Production and Lambda-driven Inflation from Quantum Einstein Gravity
We review recent work on renormalization group (RG) improved cosmologies
based upon a RG trajectory of Quantum Einstein Gravity (QEG) with realistic
parameter values. In particular we argue that QEG effects can account for the
entire entropy of the present Universe in the massless sector and give rise to
a phase of inflationary expansion. This phase is a pure quantum effect and
requires no classical inflaton field.Comment: 12 pages, 4 figures, IGCG-07 Pun
Variational Study of Weakly Coupled Triply Heavy Baryons
Baryons made of three heavy quarks become weakly coupled, when all the quarks
are sufficiently heavy such that the typical momentum transfer is much larger
than Lambda_QCD. We use variational method to estimate masses of the
lowest-lying bcc, ccc, bbb and bbc states by assuming they are Coulomb bound
states. Our predictions for these states are systematically lower than those
made long ago by Bjorken.Comment: 31 pages, 5 figure
Gravitating defects of codimension-two
Thin gravitating defects with conical singularities in higher codimensions
and with generalized Israel matching conditions are known to be inconsistent
for generic energy-momentum. A way to remove this inconsistency is proposed and
is realized for an axially symmetric gravitating codimension-two defect in six
dimensional Einstein gravity. By varying with respect to the brane embedding
fields, alternative matching conditions are derived, which are generalizations
of the Nambu-Goto equations of motion of the defect, consistent with bulk
gravity. For a maximally symmetric defect the standard picture is recovered.
The four-dimensional perfect fluid cosmology coincides with conventional FRW in
the case of radiation, but for dust it has rho^{4/3} instead of rho. A
four-dimensional black hole solution is presented having the Schwarzschild form
with a short-distance correction r^{-2}.Comment: Minor changes, to appear in Classical and Quantum Gravit
Scale-dependent metric and causal structures in Quantum Einstein Gravity
Within the asymptotic safety scenario for gravity various conceptual issues
related to the scale dependence of the metric are analyzed. The running
effective field equations implied by the effective average action of Quantum
Einstein Gravity (QEG) and the resulting families of resolution dependent
metrics are discussed. The status of scale dependent vs. scale independent
diffeomorphisms is clarified, and the difference between isometries implemented
by scale dependent and independent Killing vectors is explained. A concept of
scale dependent causality is proposed and illustrated by various simple
examples. The possibility of assigning an "intrinsic length" to objects in a
QEG spacetime is also discussed.Comment: 52 page
Boundary States of c=1 and 3/2 Rational Conformal Field Theories
We study the boundary states for the rational points in the moduli spaces of
c=1 conformal and c=3/2 superconformal field theories, including the isolated
Ginsparg points. We use the orbifold and simple-current techniques to relate
the boundary states of different theories and to obtain symmetry-breaking,
non-Cardy boundary states. We show some interesting examples of fractional and
twisted branes on orbifold spaces.Comment: Latex, 46 pages, 1 figur
Langevin dynamics of the Lebowitz-Percus model
We revisit the hard-spheres lattice gas model in the spherical approximation
proposed by Lebowitz and Percus (J. L. Lebowitz, J. K. Percus, Phys. Rev.{\
144} (1966) 251). Although no disorder is present in the model, we find that
the short-range dynamical restrictions in the model induce glassy behavior. We
examine the off-equilibrium Langevin dynamics of this model and study the
relaxation of the density as well as the correlation, response and overlap
two-time functions. We find that the relaxation proceeds in two steps as well
as absence of anomaly in the response function. By studying the violation of
the fluctuation-dissipation ratio we conclude that the glassy scenario of this
model corresponds to the dynamics of domain growth in phase ordering kinetics.Comment: 21 pages, RevTeX, 14 PS figure
N=4 superconformal mechanics as a Non linear Realization
An action for a superconformal particle is constructed using the non linear
realization method for the group PSU(1,1|2), without introducing superfields.
The connection between PSU(1,1|2) and black hole physics is discussed. The
lagrangian contains six arbitrary constants and describes a non-BPS
superconformal particle. The BPS case is obtained if a precise relation between
the constants in the lagrangian is verified, which implies that the action
becomes kappa-symmetric.Comment: new subection, references added and new acknowledgment
Jain States in a Matrix Theory of the Quantum Hall Effect
The U(N) Maxwell-Chern-Simons matrix gauge theory is proposed as an extension
of Susskind's noncommutative approach. The theory describes D0-branes,
nonrelativistic particles with matrix coordinates and gauge symmetry, that
realize a matrix generalization of the quantum Hall effect. Matrix ground
states obtained by suitable projections of higher Landau levels are found to be
in one-to-one correspondence with the expected Laughlin and Jain hierarchical
states. The Jain composite-fermion construction follows by gauge invariance via
the Gauss law constraint. In the limit of commuting, ``normal'' matrices the
theory reduces to eigenvalue coordinates that describe realistic electrons with
Calogero interaction. The Maxwell-Chern-Simons matrix theory improves earlier
noncommutative approaches and could provide another effective theory of the
fractional Hall effect.Comment: 35 pages, 3 figure
Scale-Invariance and the Strong Coupling Problem
The effective theory of adiabatic fluctuations around arbitrary
Friedmann-Robertson-Walker backgrounds - both expanding and contracting -
allows for more than one way to obtain scale-invariant two-point correlations.
However, as we show in this paper, it is challenging to produce scale-invariant
fluctuations that are weakly coupled over the range of wavelengths accessible
to cosmological observations. In particular, requiring the background to be a
dynamical attractor, the curvature fluctuations are scale-invariant and weakly
coupled for at least 10 e-folds only if the background is close to de Sitter
space. In this case, the time-translation invariance of the background
guarantees time-independent n-point functions. For non-attractor solutions, any
predictions depend on assumptions about the evolution of the background even
when the perturbations are outside of the horizon. For the simplest such
scenario we identify the regions of the parameter space that avoid both
classical and quantum mechanical strong coupling problems. Finally, we present
extensions of our results to backgrounds in which higher-derivative terms play
a significant role.Comment: 17 pages + appendices, 3 figures; v2: typos fixe
Generating Function for Particle-Number Probability Distribution in Directed Percolation
We derive a generic expression for the generating function (GF) of the
particle-number probability distribution (PNPD) for a simple reaction diffusion
model that belongs to the directed percolation universality class. Starting
with a single particle on a lattice, we show that the GF of the PNPD can be
written as an infinite series of cumulants taken at zero momentum. This series
can be summed up into a complete form at the level of a mean-field
approximation. Using the renormalization group techniques, we determine
logarithmic corrections for the GF at the upper critical dimension. We also
find the critical scaling form for the PNPD and check its universality
numerically in one dimension. The critical scaling function is found to be
universal up to two non-universal metric factors.Comment: (v1,2) 8 pages, 5 figures; one-loop calculation corrected in response
to criticism received from Hans-Karl Janssen, (v3) content as publishe
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