Inflation in Entropic Cosmology: Primordial Perturbations and non-Gaussianities. (arXiv:1011.1245v1 [hep-th] CROSS LISTED): ”
We investigate thermal inflation in double-screen entropic cosmology. We find
that its realization is general, resulting from the system evolution from
non-equilibrium to equilibrium. Furthermore, going beyond the background
evolution, we study the primordial curvature perturbations arising from the
universe interior, as well as from the thermal fluctuations generated on the
holographic screens. We show that the power spectrum is nearly scale-invariant
with a red tilt, while the tensor-to-scalar ratio is in agreement with
observations. Finally, we examine the non-Gaussianities of primordial curvature
perturbations, and we find that a sizable value of the non-linearity parameter
is possible due to holographic statistics on the outer screen.
”
A stochastic model of evolution. (arXiv:0909.2108v2 [math.PR] UPDATED): ”
We propose a stochastic model for evolution. Births and deaths of species
occur with constant probabilities. Each new species is associated with a
fitness sampled from the uniform distribution on [0,1]. Every time there is a
death event then the type that is killed is the one with the smallest fitness.
We show that there is a sharp phase transition when the birth probability is
larger than the death probability. The set of species with fitness higher than
a certain critical value approach an uniform distribution. On the other hand
all the species with fitness less than the critical disappear after a finite
(random) time.
”
Question Isotropy. (arXiv:1011.2240v1 [astro-ph.CO]): ”
The ‘cosmological principle’ was set up early without realizing its
implications for the horizon problem, and almost entirely without support from
observational data. Consistent signals of anisotropy have been found in data on
electromagnetic propagation, polarizations of QSOs and $CMB$ temperature maps.
The axis of Virgo is found again and again in signals breaking isotropy, from
independent observables in independent energy regimes. There are no
satisfactory explanations of these effects in conventional astrophysics.
Axion-photon mixing and propagation in axion condensates are capable of
encompassing the data.
”
Constraining Entropic Cosmology. (arXiv:1011.2226v1 [astro-ph.CO]): ”
It has been recently proposed that the interpretation of gravity as an
emergent, entropic force might have nontrivial implications to cosmology. Here
two approaches are investigated: in one, the Friedman equation receives
entropic contributions from the usually neglected surface terms, and in
another, the extra terms are derived from quantum corrections to the entropy
formula. UV terms may drive inflation, avoiding a recently derived no-go
theorem, though in some cases leading to a graceful exit problem. IR terms can
generate dark energy, alleviating the cosmological constant problem. The
quantum corrections are bounded by their implications to the BBN, and the
surface terms are constrained in addition by their effect upon the behavior of
matter. Likelihood analyses are performed to constrain the modifications by the
SNeIa, BAO and CMB data. It is found that a monomial correction to the
area-entropy formula results in late acceleration in very good agreement with
observations, which then turn out to be compatible with positive curvature. The
evolution of perturbations is deduced by assuming the Jebsen-Birkhoff theorem.
Distinct signatures can then be identified in the large scale structure
formation. Furthermore, it is shown that the visible universe satisfies the
Bekenstein bound.
”
Breaking of de Sitter Symmetry. (arXiv:1011.2241v1 [hep-th]): ”
We show that an interacting spin-0 field on a de Sitter space background will
break the underlying de Sitter symmetry. This is done first for a (1+1) de
Sitter space where a boson-fermion correspondence permits us to solve certain
interacting theories by transforming them into free ones of opposite
statistics. A massless boson interacting by a sine-Gordon potential is shown to
be equivalent to a free massive fermion with the mass depending on the de
Sitter time thus breaking the symmetry explicitly. We then show that for larger
dimensions and any boson potential, to one loop, an anomaly develops and the
currents generating the de Sitter transformations are not conserved.
”
The Wall of Fundamental Constants. (arXiv:1011.1504v1 [astro-ph.CO]): ”
We consider the signatures of a domain wall produced in the spontaneous
symmetry breaking involving a dilaton-like scalar field coupled to
electromagnetism. Domains on either side of the wall exhibit slight differences
in their respective values of the fine-structure constant, alpha. If such a
wall is present within our Hubble volume, absorption spectra at large redshifts
may or may not provide a variation in alpha relative to the terrestrial value,
depending on our relative position with respect to the wall. This wall could
resolve the “contradiction” between claims of a variation of alpha based on
Keck/Hires data and of the constancy of alpha based on VLT data. We derive the
properties of the wall and the parameters of the underlying microscopic model
required to reproduce the possible spatial variation of alpha. We discuss the
constraints on the existence of the low-energy domain wall and describe its
observational implications concerning the variation of the fundamental
constants.
”
Curvature Perturbations and non-Gaussianities from Waterfall Phase Transition during Inflation. (arXiv:1010.6292v1 [astro-ph.CO]): ”
We consider a variant of hybrid inflation where the waterfall phase
transition happens during inflation. By adjusting the parameters associated
with the mass of the waterfall field, we arrange that the phase transition is
not sharp so inflation can proceed for an extended period after the waterfall
phase transition. We show that one can work in the limit where the quantum
back-reactions are subdominant compared to the classical back-reactions. It is
shown that significant amount of large scale curvature perturbations are
induced from the entropy perturbations. The curvature perturbations spectral
index runs from a blue spectrum to a red spectrum depending on whether the mode
of interest leaves the horizon before the phase transition or after the phase
transition. This can have interesting observational consequences on CMB. The
non-Gaussianity parameter $f_{NL}$ is calculated to be $\lesssim 1$ but much
bigger than the slow-roll parameters.
”
A theory of extra radiation in the Universe. (arXiv:1010.5693v1 [hep-ph]): ”
Recent cosmological observations, such as the measurement of the primordial
4He abundance, CMB, and large scale structure, give preference to the existence
of extra radiation component, Delta N_nu > 0. The extra radiation may be
accounted for by particles which were in thermal equilibrium and decoupled
before the big bang nucleosynthesis. Broadly speaking, there are two
possibilities: 1) there are about 10 particles which have very weak couplings
to the standard model particles and decoupled much before the QCD phase
transition; 2) there is one or a few light particles with a reasonably strong
coupling to the plasma and it decouples after the QCD phase transition.
Focusing on the latter case, we find that a light chiral fermion is a suitable
candidate, which evades astrophysical constraints. Interestingly, such a
scenario may be confirmed at the LHC. As a concrete example, we show that such
a light fermion naturally appears in the E_6-inspired GUT.
”
Elementary Quantum Mechanics in a Space-time Lattice. (arXiv:1011.2544v1 [quant-ph]): ”
Studies of quantum fields and gravity suggest the existence of a minimal
length, such as Planck length \cite{Floratos,Kempf}. It is natural to ask how
the existence of a minimal length may modify the results in elementary quantum
mechanics (QM) problems familiar to us \cite{Gasiorowicz}. In this paper we
address a simple problem from elementary non-relativistic quantum mechanics,
called ‘particle in a box’, where the usual continuum (1+1)-space-time is
supplanted by a space-time lattice. Our lattice consists of a grid of
$\lambda_0 \times \tau_0 $ rectangles, where $\lambda_0$, the lattice
parameter, is a fundamental length (say Planck length) and, we take $\tau_0$ to
be equal to $\lambda_0/c$. The corresponding Schrodinger equation becomes a
difference equation, the solution of which yields the $q$-eigenfunctions and
$q$-eigenvalues of the energy operator as a function of $\lambda_0 $. The
$q$-eigenfunctions form an orthonormal set and both $q$-eigenfunctions and
$q$-eigenvalues reduce to continuum solutions as $ \lambda_0 \rightarrow 0 .$
The corrections to eigenvalues because of the assumed lattice is shown to be
$O(\lambda_0^2).$ We then compute the uncertainties in position and momentum,
$\Delta x, \Delta p$ for the box problem and study the consequent modification
of Heisenberg uncertainty relation due to the assumption of space-time lattice,
in contrast to modifications suggested by other investigations such as
\cite{Floratos}.
”
A unified framework for biological evolution and stochastic quantization. (arXiv:1011.1883v1 [cond-mat.stat-mech] CROSS LISTED): ”
We investigate the profound relation between the equations of biological
evolution and quantum mechanics by writing a biologically inspired equation for
the stochastic dynamics of an ensemble of particles. Interesting behavior is
observed which is related to a new type of stochastic quantization. We find
that the probability distribution of the ensemble of particles can be
decomposed into eigenfunctions associated to a discrete spectrum of
eigenvalues. In absence of interactions between the particles, the
out-of-equilibrium dynamics asymptotically relaxes towards the fundamental
state. This phenomenon can be related with the Fisher theorem in biology. On
the contrary, in presence of scattering processes the evolution reaches a
steady state in which the distribution of the ensemble of particles is
characterized by a Bose-Einstein statistics. In order to show a concrete
example of this stochastic quantization we have solved explicitly the case in
which the potential energy has the harmonic oscillator form.
”
Non-linear corrections to inflationary power spectrum. (arXiv:1011.2572v1 [astro-ph.CO]): ”
We study non-linear contributions to the power spectrum of the curvature
perturbation on super-horizon scales, produced during slow-roll inflation
driven by a canonical single scalar field. We find that on large scales the
linear power spectrum completely dominates and leading non-linear corrections
remain totally negligible, indicating that we can safely rely on linear
perturbation theory to study inflationary power spectrum. We also briefly
comment on the infrared and ultraviolet behaviour of the non-linear
corrections.
”
A Symbolic Summation Approach to Feynman Integral Calculus. (arXiv:1011.2656v1 [cs.SC]): ”
Given a Feynman parameter integral, depending on a single discrete variable
$N$ and a real parameter $\epsilon$, we discuss a new algorithmic framework to
compute the first coefficients of its Laurent series expansion in $\epsilon$.
In a first step, the integrals are expressed by hypergeometric multi-sums by
means of symbolic transformations. Given this sum format, we develop new
summation tools to extract the first coefficients of its series expansion
whenever they are expressible in terms of indefinite nested product-sum
expressions. In particular, we enhance the known multi-sum algorithms to derive
recurrences for sums with complicated boundary conditions, and we present new
algorithms to find formal Laurent series solutions of a given recurrence
relation.
“
Um passeio aleatório 