4,086 research outputs found
Conformal fixed point, Cosmological Constant and Quintessence
We connect a possible solution for the ``cosmological constant problem'' to
the existence of a (postulated) conformal fixed point in a fundamental theory.
The resulting cosmology leads to quintessence, where the present acceleration
of the expansion of the universe is linked to a crossover in the flow of
coupling constants.Comment: More detailed discussion of quantum fluctuations,update with
WMAP-data,4 pages,LaTe
Nonexistence of random gradient Gibbs measures in continuous interface models in
We consider statistical mechanics models of continuous spins in a disordered
environment. These models have a natural interpretation as effective interface
models. It is well known that without disorder there are no interface Gibbs
measures in infinite volume in dimension , while there are ``gradient
Gibbs measures'' describing an infinite-volume distribution for the increments
of the field, as was shown by Funaki and Spohn. In the present paper we show
that adding a disorder term prohibits the existence of such gradient Gibbs
measures for general interaction potentials in . This nonexistence result
generalizes the simple case of Gaussian fields where it follows from an
explicit computation. In where random gradient Gibbs measures are
expected to exist, our method provides a lower bound of the order of the
inverse of the distance on the decay of correlations of Gibbs expectations
w.r.t. the distribution of the random environment.Comment: Published in at http://dx.doi.org/10.1214/07-AAP446 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Grover's quantum searching algorithm is optimal
I improve the tight bound on quantum searching by Boyer et al.
(quant-ph/9605034) to a matching bound, thus showing that for any probability
of success Grovers quantum searching algorithm is optimal. E.g. for near
certain success we have to query the oracle pi/4 sqrt{N} times, where N is the
size of the search space. I also show that unfortunately quantum searching
cannot be parallelized better than by assigning different parts of the search
space to independent quantum computers. Earlier results left open the
possibility of a more efficient parallelization.Comment: 13 pages, LaTeX, essentially published versio
Schroedinger Invariance from Lifshitz Isometries in Holography and Field Theory
We study non-relativistic field theory coupled to a torsional Newton-Cartan
geometry both directly as well as holographically. The latter involves gravity
on asymptotically locally Lifshitz space-times. We define an energy-momentum
tensor and a mass current and study the relation between conserved currents and
conformal Killing vectors for flat Newton-Cartan backgrounds. It is shown that
flat NC space-time realizes two copies of the Lifshitz algebra that together
form a Schroedinger algebra (without the central element). We show why the
Schroedinger scalar model has both copies as symmetries and the Lifshitz scalar
model only one. Finally we discuss the holographic dual of this phenomenon by
showing that the bulk Lifshitz space-time realizes the same two copies of the
Lifshitz algebra.Comment: 5 pages, modified abstract, clarifications added, typos fixed, refs
update
Non-Equilibrium Time Evolution in Quantum Field Theory
The time development of equal-time correlation functions in quantum mechanics
and quantum field theory is described by an exact evolution equation for
generating functionals. This permits a comparison between classical and quantum
evolution in non-equilibrium systems.Comment: 7 pages, LaTe
Mass freezing in growing neutrino quintessence
Growing neutrino quintessence solves the coincidence problem for dark energy
by a growing cosmological value of the neutrino mass which emerges from a
cosmon-neutrino interaction stronger than gravity. The cosmon-mediated
attraction between neutrinos induces the formation of large scale neutrino
lumps in a recent cosmological epoch. We argue that the non-linearities in the
cosmon field equations stop the further increase of the neutrino mass within
sufficiently dense and large lumps. As a result, we find the neutrino induced
gravitational potential to be substantially reduced when compared to linear
extrapolations. We furthermore demonstrate that inside a lump the possible time
variation of fundamental constants is much smaller than their cosmological
evolution. This feature may reconcile current geophysical bounds with claimed
cosmological variations of the fine structure constant.Comment: 15 pages, 12 figures. Version published in PR
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