11,697 research outputs found
Fluid Membranes and 2d Quantum Gravity
We study the RG flow of two dimensional (fluid) membranes embedded in
Euclidean D-dimensional space using functional RG methods based on the
effective average action. By considering a truncation ansatz for the effective
average action with both extrinsic and intrinsic curvature terms we derive a
system of beta functions for the running surface tension, bending rigidity and
Gaussian rigidity. We look for non-trivial fixed points but we find no evidence
for a crumpling transition at . Finally, we propose to identify the
limit of the theory with two dimensional quantum gravity. In
this limit we derive new beta functions for both cosmological and Newton's
constants.Comment: 16 pages, 1 figur
The Wishart short rate model
We consider a short rate model, driven by a stochastic process on the cone of
positive semidefinite matrices. We derive sufficient conditions ensuring that
the model replicates normal, inverse or humped yield curves
The depletion in Bose Einstein condensates using Quantum Field Theory in curved space
Using methods developed in Quantum Field Theory in curved space we can
estimate the effects of the inhomogeneities and of a non vanishing velocity on
the depletion of a Bose Einstein condensate within the hydrodynamical
approximation.Comment: 4 pages, no figure. Discussion extended and references adde
Has the Quark-Gluon Plasma been seen?
Data from the first three years of running at RHIC are reviewed and put into
context with data obtained previously at the AGS and SPS and with the physics
question of creation of a quark-gluon plasma in high energy heavy ion
collisions. Also some very recent and still preliminary data from run4 are
included.Comment: plenary paper, Lepton-Photon 2005, Uppsala, Swede
Determining the Neutrino Mass Hierarchy with Cosmology
The combination of current large scale structure and cosmic microwave
background (CMB) anisotropies data can place strong constraints on the sum of
the neutrino masses. Here we show that future cosmic shear experiments, in
combination with CMB constraints, can provide the statistical accuracy required
to answer questions about differences in the mass of individual neutrino
species. Allowing for the possibility that masses are non-degenerate we combine
Fisher matrix forecasts for a weak lensing survey like Euclid with those for
the forthcoming Planck experiment. Under the assumption that neutrino mass
splitting is described by a normal hierarchy we find that the combination
Planck and Euclid will possibly reach enough sensitivity to put a constraint on
the mass of a single species. Using a Bayesian evidence calculation we find
that such future experiments could provide strong evidence for either a normal
or an inverted neutrino hierachy. Finally we show that if a particular neutrino
hierachy is assumed then this could bias cosmological parameter constraints,
for example the dark energy equation of state parameter, by > 1\sigma, and the
sum of masses by 2.3\sigma.Comment: 9 pages, 6 figures, 3 table
Semiclassical Gravity in the Far Field Limit of Stars, Black Holes, and Wormholes
Semiclassical gravity is investigated in a large class of asymptotically
flat, static, spherically symmetric spacetimes including those containing
static stars, black holes, and wormholes. Specifically the stress-energy
tensors of massless free spin 0 and spin 1/2 fields are computed to leading
order in the asymptotic regions of these spacetimes. This is done for spin 0
fields in Schwarzschild spacetime using a WKB approximation. It is done
numerically for the spin 1/2 field in Schwarzschild, extreme
Reissner-Nordstrom, and various wormhole spacetimes. And it is done by finding
analytic solutions to the leading order mode equations in a large class of
asymptotically flat static spherically symmetric spacetimes. Agreement is shown
between these various computational methods. It is found that for all of the
spacetimes considered, the energy density and pressure in the asymptotic region
are proportional to 1/r^5 to leading order. Furthermore, for the spin 1/2 field
and the conformally coupled scalar field, the stress-energy tensor depends only
on the leading order geometry in the far field limit. This is also true for the
minimally coupled scalar field for spacetimes containing either a static star
or a black hole, but not for spacetimes containing a wormhole.Comment: 43 pages, 2 figures. Reference added, minor changes, PRD versio
Opinion formation models based on game theory
A way to simulate the basic interactions between two individuals with
different opinions, in the context of strategic game theory, is proposed.
Various games are considered, which produce different kinds of opinion
formation dynamics. First, by assuming that all individuals (players) are
equals, we obtain the bounded confidence model of continuous opinion dynamics
proposed by Deffuant et al. In such a model a tolerance threshold is defined,
such that individuals with difference in opinion larger than the threshold can
not interact. Then, we consider that the individuals have different
inclinations to change opinion and different abilities in convincing the
others. In this way, we obtain the so-called ``Stubborn individuals and
Orators'' (SO) model, a generalization of the Deffuant et al. model, in which
the threshold tolerance is different for every couple of individuals. We
explore, by numerical simulations, the dynamics of the SO model, and we propose
further generalizations that can be implemented.Comment: 18 pages, 4 figure
Measurability of the tidal polarizability of neutron stars in late-inspiral gravitational-wave signals
The gravitational wave signal from a binary neutron star inspiral contains
information on the nuclear equation of state. This information is contained in
a combination of the tidal polarizability parameters of the two neutron stars
and is clearest in the late inspiral, just before merger. We use the recently
defined tidal extension of the effective one-body formalism to construct a
controlled analytical description of the frequency-domain phasing of neutron
star inspirals up to merger. Exploiting this analytical description we find
that the tidal polarizability parameters of neutron stars can be measured by
the advanced LIGO-Virgo detector network from gravitational wave signals having
a reasonable signal-to-noise ratio of . This measurability result
seems to hold for all the nuclear equations of state leading to a maximum mass
larger than . We also propose a promising new way of extracting
information on the nuclear equation of state from a coherent analysis of an
ensemble of gravitational wave observations of separate binary merger events.Comment: 28 pages, 6 figures. Submitted to Phys. Rev.
Functional Renormalization of Noncommutative Scalar Field Theory
In this paper we apply the Functional Renormalization Group Equation (FRGE)
to the non-commutative scalar field theory proposed by Grosse and Wulkenhaar.
We derive the flow equation in the matrix representation and discuss the theory
space for the self-dual model. The features introduced by the external
dimensionful scale provided by the non-commutativity parameter, originally
pointed out in \cite{Gurau:2009ni}, are discussed in the FRGE context. Using a
technical assumption, but without resorting to any truncation, it is then shown
that the theory is asymptotically safe for suitably small values of the
coupling, recovering the result of \cite{disertori:2007}. Finally, we
show how the FRGE can be easily used to compute the one loop beta-functions of
the duality covariant model.Comment: 38 pages, no figures, LaTe
Planck scale inflationary spectra from quantum gravity
We derive the semiclassical evolution of massless minimally coupled scalar
matter in the de Sitter space-time from the Born-Oppenheimer reduction of the
Wheeler-DeWitt equation. We show that the dynamics of trans-Planckian modes can
be cast in the form of an effective modified dispersion relation and that high
energy corrections in the power spectrum of the cosmic microwave background
radiation produced during inflation remain very small if the initial state is
the Bunch-Davies vacuum.Comment: 6 pages, no figures, final version to appear in PR
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