199684483
LOOP QUANTUM GRAVITY AND ULTRA HIGH ENERGY COSMIC RAYS
A device for introducing particles into an analyzer of dustiness of a gaseous medium comprises a cell having a transparent cover with a microscope arranged thereabove. A through guide duct is made in a wall of the cell, while provided in the bottom of the latter are a vertical feed duct communicating with the dustiness analyzer and a horizontal channel which is an extension of the through guide duct and intersects the vertical feed duct. The device also comprises a source of a pure gaseous medium which is fed under pressure into the through guide duct wherewith the source communicates.
58905616
Loop quantum gravity corrections and cosmic rays decays
Loop quantum gravity effective theories are reviewed in the context of the observed GZK limit anomaly and related processes. This is accomplished through a kinematical analysis of the modified threshold conditions for the involved decay reactions, arising from the theory. Specially interesting is the possibility of an helicity dependant violation of the limit, whose primary effect would be the observation of favoured helicity states for highly energetic particles.
120515364
Observational Constraints on the Braneworld Geometry
15031265
On Newton's law in supersymmetric braneworld models
We study the propagation of gravitons within 5-D supersymmetric braneworld models with a bulk scalar field. The setup considered here consists of a 5-D bulk spacetime bounded by two 4-D branes localized at the fixed points of an S1/2 orbifold. There is a scalar field in the bulk which, given a superpotential W(), determines the warped geometry of the 5-D spacetime. This type of scenario is common in string theory, where the bulk scalar field is related to the volume of small compact extra dimensions. We show that, after the moduli are stabilized by supersymmetry breaking terms localized on the branes, the only relevant degrees of freedom in the bulk consist of a 5-D massive spectrum of gravitons. Then we analyze the gravitational interaction between massive bodies localized at the positive tension brane mediated by these bulk gravitons. It is shown that the Newtonian potential describing this interaction picks up a non-trivial contribution at short distances that depends on the shape of the superpotential W(). We compute this contribution for dilatonic braneworld scenarios W() eα (where α is a constant) and discuss the particular case of 5-D Heterotic M-theory: It is argued that a specific footprint at micron scales could be observable in the near future.
18075993
Inflation with a stringy minimal length, reworked
In this paper we revisit the formulation of scalar field theories on de Sitter backgrounds subject to the generalized uncertainty principle (GUP). The GUP arises in several contexts in string theory, but is most readily thought of as resulting from using strings as effective probes of geometry, which suggests an uncertainty relation incorporating the string scale ls. After reviewing the string theoretic case for the GUP, which implies a minimum length scale ls, we follow in the footsteps of Kempf and concern ourselves with how one might write down field theories which respect the GUP. We uncover a new representation of the GUP, which unlike previous studies, readily permits exact analytical solutions for the mode functions of a scalar field on de Sitter backgrounds. We find that scalar fields cannot be quantized on inflationary backgrounds with a Hubble radius H−1 smaller than the string scale, implying a sensibly stringy (as opposed to Planckian) cutoff on the scale of inflation resulting from the GUP. We also compute (Hls)2 corrections to the two point correlation function analytically and comment on the future prospects of observing such corrections in the fortunate circumstance our universe is described by a very weakly coupled string theory.
119168398
Bigravitational inflation
We study the realization of cosmic inflation in bigravity theories. By analyzing the evolution of scalar, vector and tensor perturbations in de Sitter-like spacetimes, we find strong stability constraints on the class of viable vacua offered by these theories. More specifically, the only stable de Sitter vacua contain two nondecoupled gravitons (one of which is massive) with different maximal propagation speeds. We derive an effective theory for the massless graviton, which is found to propagate at an intermediate speed, limited by the two maximal values. For inflation, while the spectrum of density perturbations remains nearly scale invariant, the power spectrum of tensor modes is found to depart from the usual prediction found in standard slow-roll inflation. In particular, both the tensor to scalar ratio r and the spectral index of tensor modes nT receive sizable contributions from the couplings of the theory, leading to specific signals that may be tested in future cosmological probes of CMB-polarization.
14281658
A self consistent study of the phase transition in the scalar electroweak theory at finite temperature
We propose the study of the phase transition in the scalar electroweak theory at finite temperature by a two — step method. It combines i) dimensional reduction to a 3 — dimensional lattice theory via perturbative blockspin transformation, and ii) either further real space renormalization group transformations, or solution of gap equations, for the 3d lattice theory. A gap equation can be obtained by using the Peierls inequality to find the best quadratic approximation to the 3d action. This method avoids the lack of self consistency of the usual treatments which do not separate infrared and UV-problems by introduction of a lattice cutoff. The effective 3d lattice action could also be used in computer simulations.
119486225
Resonance enhancement of particle production during reheating
We found a consistent equation of reheating after inflation which shows that for small quantum fluctuations the frequencies of resonance are slighted different from the standard ones. Quantum interference is taken into account and we found that at large fluctuations the process mimics very well the usual parametric resonance, but proceeds in a different dynamical way. The analysis is made in a toy quantum mechanical model and we discuss further its extension to quantum field theory.
118478824
A non-perturbative argument for the non-abelian Higgs mechanism
Abstract The evasion of massless Goldstone bosons by the non-abelian Higgs mechanism is proved by a non-perturbative argument in the local BRST gauge.
119459248
Analytic calculation of the 1-loop effective action for the O(N+1)-symmetric 2-dimensional nonlinear sigma-model
Polyakov's calculation of the effective action for the 2d nonlinear sigma-Model is generalized by purely analytic means to include contributions which are not UV-divergent and which depend on the choice of block spin. An analytic approximation to the background field which determines the classical perfect action is given, and approximations to the 1-loop correction are found. The results should be useful for numerical simulations.
118167913
Analytical computation of the magnetization probability density function for the harmonic 2D XY model
The probability density function (PDF) of some global average quantity plays a fundamental role in critical and highly correlated systems. We explicitly compute this quantity as a function of the magnetization for the two dimensional XY model in its harmonic approximation. Numerical simulations and perturbative results have shown a Gumbel-like shape of the PDF, in spite of the fact that the average magnetization is not an extreme variable. Our analytical result allows to test both perturbative analytical expansions and also numerical computations performed previously. Perfect agreement is found for the first moments of the PDF. Also for large volume and in the high temperature limit the distribution becomes Gaussian, as it should be. In the low temperature regime its numerical evaluation is compatible with a Gumbel distribution.