Arquivo da categoria: Física

ArXiv highlights, vol.7


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.

Anúncios

Acta Physica, Phygg & Inspire


Bom, parece que os físicos estamos nos tornando mais sociáveis. Ou pelo menos tentando…

Acta Physica (AP) é uma rede social que visa integrar os físicos de todo o mundo de um modo parecido com o Myspace, Orkut e Facebook. Disse “modo parecido” pois a implementação não é, na minha opinião, tão boa quanto a dessas redes sociais mais populares. O serviço conta com grupos (equivalente às comunidades do Orkut), um fórum de discussões, um blog pessoal + perfil (seria equivalente à página “perfil” do Orkut) onde você pode inclusive importar seus tweets, serviço de bookmarks, chat, adição de amigos etc etc. Acho a idéia extremamente boa, mas tem algumas coisas que me desagradam, como o excesso de propagandas e a possibilidade de qualquer pessoa, físico ou não, entrar na comunidade, o que faz com que haja por lá alguns trolls e “físicos de araque” com suas teorias mirabolantes, o que baixa o nível da rede social. Me parece também que o AP não se tornou muito popular na comunidade física, pois o mesmo conta apenas com cerca de 600 membros. Acho que se um serviço como esse fosse criado, mantido e organizado por um esforço comum dos grandes “journals” da Física ele daria bons frutos. Um sistema top-down de distribuição de convites solucionaria a questão da seleção de membros. Poderia haver uma distribuição inicial de convites para os “grandes” da Física, que por sua vez iriam distribuindo para seus colaboradores e assim sucessivamente. Com o tempo, fatalmente chegaria um convite para seu orientador e depois para você. Mais informações: http://www.actaphysica.com/

Outro serviço interessante, e pra mim muito mais promissor que o Acta Physica, é o Phygg, essencialmente um Digg para preprints de Física! O funcionamento é essencialmente o mesmo que o da já consagrada rede social: você vê um artigo do arXiv e pode votar positivamente ou negativamente nele. Você pode ainda criar uma discussão em torno do preprint através de comentários públicos, salvá-lo no seu bookmark e compartilhá-lo dentro do grupo no qual você participa. Essa ferramenta é fantástica para quem trabalha num grupo de pesquisa. O site ainda mantém uma página perfil para cada membro com suas estatísticas pessoais. Um ponto negativo é que o Phygg não conta com todas as categorias presentes no arXiv.  Mais informações: http://phygg.com/phygg/.

Por fim, temos uma novidade no famoso Spires: desde o início do mês já estão recomendando a migração para a nova interface do serviço, que passa a se chamar Inspire. Foram implementadas diversas melhorias no sistema de buscas, entre outras. O endereço é http://inspirebeta.net/

Até a próxima!

ArXiv highlights, vol. 6


Physical consequences of P$\neq$NP. (arXiv:1010.0128v2 [quant-ph] UPDATED): “

Computational complexity theory is applied to simulations of adiabatic
quantum computation, providing predictions about the existence of quantum phase
transitions in certain disordered systems. Moreover, bounds on their
entanglement entropy at criticality are given. Concretely, physical
consequences are drawn from the assumption that the complexity classes P and NP
differ.

Quantum ChromoDynamics. (arXiv:1010.2330v1 [hep-ph]): “

These lectures on QCD stress the theoretical elements that underlie a wide
range of phenomenological studies, particularly gauge invariance,
renormalization, factorization and infrared safety. The three parts cover the
basics of QCD, QCD at tree level, and higher order corrections.

Statistical properties of entropy production derived from fluctuation theorems. (arXiv:1010.2319v1 [cond-mat.stat-mech]): “

Several implications of well-known fluctuation theorems, on the statistical
properties of the entropy production, are studied using various approaches. We
begin by deriving a tight lower bound on the variance of the entropy production
for a given mean of this random variable. It is shown that the Evans-Searles
fluctuation theorem alone imposes a significant lower bound on the variance
only when the mean entropy production is very small. It is then nonetheless
demonstrated that upon incorporating additional information concerning the
entropy production, this lower bound can be significantly improved, so as to
capture extensivity properties. Another important aspect of the fluctuation
properties of the entropy production is the relationship between the mean and
the variance, on the one hand, and the probability of the event where the
entropy production is negative, on the other hand. Accordingly, we derive upper
and lower bounds on this probability in terms of the mean and the variance.
These bounds are tighter than previous bounds that can be found in the
literature. Moreover, they are tight in the sense that there exist probability
distributions, satisfying the Evans-Searles fluctuation theorem, that achieve
them with equality. Finally, we present a general method for generating a wide
class of inequalities that must be satisfied by the entropy production. We use
this method to derive several new inequalities which go beyond the standard
derivation of the second law.

Techniques for n-Particle Irreducible Effective Theories. (arXiv:1010.2978v1 [hep-ph]): “

In this paper we show that the skeleton diagrams in the m-Loop nPI effective
action correspond to an infinite resummation of perturbative diagrams which is
void of double counting at the m-Loop level. We also show that the variational
equations of motion produced by the n-Loop nPI effective theory are equivalent
to the Schwinger-Dyson equations, up to the order at which they are consistent
with the underlying symmetries of the original theory. We use a diagrammatic
technique to obtain the 5-Loop 5PI effective action for a scalar theory with
cubic and quartic interactions, and verify that the result satisfies these two
statements.

An overview of the theories of the glass transition. (arXiv:1010.2938v1 [cond-mat.stat-mech]): “

The topic of the glass transition gives rise to a a wide diversity of views.
It is, accordingly, characterized by a lack of agreement on which would be the
most profitable theoretical perspective. In this chapter, I provide some
elements that can help sorting out the many theoretical approaches,
understanding their foundations, as well as discussing their validity and
mutual compatibility. Along the way, I describe the progress made in the last
twenty years, including new insights concerning the spatial heterogeneity of
the dynamics and the characteristic length scales associated with the glass
transition. An emphasis is put on those theories that associate glass formation
with growing collective behavior and emerging universality.

Particle cosmology. (arXiv:1010.2642v1 [hep-ph]): “

In these lectures the present status of the so-called standard cosmological
model, based on the hot Big Bang theory and the inflationary paradigm is
reviewed. Special emphasis is given to the origin of the cosmological
perturbations we see today under the form of the cosmic microwave background
anisotropies and the large scale structure and to the dark matter and dark
energy puzzles.

High-energy astroparticle physics. (arXiv:1010.2647v1 [hep-ph]): “

In these three lectures I discuss the present status of high-energy
astroparticle physics including Ultra-High-Energy Cosmic Rays (UHECR),
high-energy gamma rays, and neutrinos. The first lecture is devoted to
ultra-high-energy cosmic rays. After a brief introduction to UHECR I discuss
the acceleration of charged particles to highest energies in the astrophysical
objects, their propagation in the intergalactic space, recent observational
results by the Auger and HiRes experiments, anisotropies of UHECR arrival
directions, and secondary gamma rays produced by UHECR. In the second lecture I
review recent results on TeV gamma rays. After a short introduction to
detection techniques, I discuss recent exciting results of the H.E.S.S., MAGIC,
and Milagro experiments on the point-like and diffuse sources of TeV gamma
rays. A special section is devoted to the detection of extragalactic magnetic
fields with TeV gamma-ray measurements. Finally, in the third lecture I discuss
Ultra-High-Energy (UHE) neutrinos. I review three different UHE neutrino
detection techniques and show the present status of searches for diffuse
neutrino flux and point sources of neutrinos.

Fundamental physics in observational cosmology. (arXiv:1009.4327v1 [astro-ph.CO]): “

I discuss, through a few examples, how observational cosmology can provide
insights on hypothetical fundamental physics phenomena or mechanisms, such as
Grand Unified Theory, Superstring alternatives to the inflation paradigm, and
inflation itself.

Identifying the Inflaton. (arXiv:1009.3741v1 [astro-ph.CO]): “

We explore the ability of experimental physics to uncover the underlying
structure of the gravitational Lagrangian responsible for inflation. It is a
common expectation that improved measurements of the primordial perturbations
will result in a better understanding of the nature of the inflaton field. We
investigate to what extent this expectation is justifiable within the context
of a general inflationary Lagrangian. Our conclusion is that observables beyond
the adiabatic and tensor two-point functions on CMB scales are needed; in
particular, isocurvature modes or a combination of local non-Gaussiantities and
a precision measurement of the tensor spectral index will enable the most
successful reconstructions. We show that amongst these observables, the most
powerful probe of the inflationary Lagrangian is a precision measurement of the
tensor spectral index, as might be possible with a direct detection of
primordial gravitational waves.

The World as Evolving Information. (arXiv:0704.0304v3 [cs.IT] CROSS LISTED): “

This paper discusses the benefits of describing the world as information,
especially in the study of the evolution of life and cognition. Traditional
studies encounter problems because it is difficult to describe life and
cognition in terms of matter and energy, since their laws are valid only at the
physical scale. However, if matter and energy, as well as life and cognition,
are described in terms of information, evolution can be described consistently
as information becoming more complex.

The paper presents eight tentative laws of information, valid at multiple
scales, which are generalizations of Darwinian, cybernetic, thermodynamic,
psychological, philosophical, and complexity principles. These are further used
to discuss the notions of life, cognition and their evolution.

That’s all folks!

IOP Publishing: read JPCS and other published papers online today from the Nobel Prize 2010 winners


Dear colleague,

To celebrate the 2010 Nobel Prize for Physics, IOP Publishing is making all the work previously published with us by this year’s winners open access until the end of 2010.

The Nobel Prize in Physics 2010 was jointly awarded to:

Professor Andre Geim
Dr Kostya Novoselov

For ‘groundbreaking experiments regarding the two-dimensional material graphene’.  Both physicists work at the University of Manchester in the UK.

You can read their work published with IOP Publishing at http://herald.iop.org/npjpcs/m418/zea//link/3935

In addition, Physica Scripta, which is published on behalf of the Physical Societies of the Nordic Countries by IOP Publishing and the Royal Swedish Academy of Sciences, is pleased to announce a new publishing initiative with the Nobel Foundation http://nobelprize.org/.  Physica Scripta will publish copies of the biographies of the 2009 Nobel Prize winners along with their lectures given at the prize ceremony.

You can read the biographies and lectures given by C K Kao, W S Boyle and G E Smith at the Physica Scripta website: http://herald.iop.org/psnobelpage/m304/zea//link/3937

Best wishes,

Graham Douglas
Publisher
iopscience.org/jpcs
jpcs@iop.org

P.S. If you think your colleagues would enjoy reading this special collection, please forward this e-mail to them.
*Data Protection*
The Institute of Physics (and other companies in its group, including IOP Publishing Limited) may like to send you further notifications like this.  If you would prefer not to receive these, then please reply to this e-mail with the word “unsubscribe” in the subject line.  We will never rent or sell your e-mail address to any third parties.

Um texto que merece ser lido, vol. 3


O texto em questão é um “artigo-comentário” do nobelista (1977) Philip W. Anderson  cujo título é  “Brainwashed by Feynman?“. O texto, de nome bastante sugestivo, foi publicado originalmente na revista Physics Today, e trata do uso algumas vezes indevido e das limitações da boa e velha teoria de perturbação.

Aqui vai o link para o artigo, que é de livre acesso: http://tinyurl.com/233w99w

Encontrei a referência para esse texto no blog Condensed Concepts.,

Até a próxima!

ArXiv & papers highlights, vol. 5


Preheating in bubble collisions: “Author(s): Jun Zhang and Yun-Song Piao
In a landscape with metastable minima, the bubbles will inevitably nucleate. We show that when the bubbles collide, due to the dramatic oscillation of the field at the collision region, the energy deposited in the bubble walls can be efficiently released by the explosive production of the particles….
[Phys. Rev. D 82, 043507] Published Thu Aug 05, 2010”

Inflation from supersymmetric quantum cosmology: “Author(s): J. Socorro and Marco D’Oleire
We derive a special scalar field potential using the anisotropic Bianchi type I cosmological model from canonical quantum cosmology under determined conditions in the evolution to anisotropic variables β_{±} . In the process, we obtain a family of potentials that has been introduced by hand in the…
[Phys. Rev. D 82, 044008] Published Thu Aug 05, 2010”

Two pieces of folklore in the AdS/CFT duality: “Author(s): Kengo Maeda, Makoto Natsuume, and Takashi Okamura
In the AdS/CFT duality, it is often said that a local symmetry in a bulk theory corresponds to a global symmetry in the corresponding boundary theory, but the global symmetry can become local when one couples with an external source. As a result, the Gubser-Klebanov-Polyakov-Witten relation gives a …
[Phys. Rev. D 82, 046002] Published Thu Aug 05, 2010”

Inflation in models with conformally coupled scalar fields: An application to the noncommutative spectral action: “Author(s): Michel Buck, Malcolm Fairbairn, and Mairi Sakellariadou
Slow-roll inflation is studied in theories where the inflaton field is conformally coupled to the Ricci scalar. In particular, the case of Higgs field inflation in the context of the noncommutative spectral action is analyzed. It is shown that while the Higgs potential can lead to the slow-roll cond…
[Phys. Rev. D 82, 043509] Published Fri Aug 06, 2010”

CMB in a box: Causal structure and the Fourier-Bessel expansion: “Author(s): L. Raul Abramo, Paulo H. Reimberg, and Henrique S. Xavier
This paper makes two points. First, we show that the line-of-sight solution to cosmic microwave anisotropies in Fourier space, even though formally defined for arbitrarily large wavelengths, leads to position-space solutions which only depend on the sources of anisotropies inside the past light cone…
[Phys. Rev. D 82, 043510] Published Fri Aug 06, 2010”

Naturality, unification, and dark matter: “Author(s): Kimmo Kainulainen, Kimmo Tuominen, and Jussi Virkajärvi
We consider a model where electroweak symmetry breaking is driven by technicolor dynamics with minimal particle content required for walking coupling and saturation of global anomalies. Furthermore, the model features three additional Weyl fermions singlet under technicolor interactions, two of whic…
[Phys. Rev. D 82, 043511] Published Fri Aug 06, 2010”

TeV scale dark matter and electroweak radiative corrections: “Author(s): Paolo Ciafaloni and Alfredo Urbano
Recent anomalies in cosmic rays data, namely, from the PAMELA Collaboration, can be interpreted in terms of TeV scale decaying/annihilating dark matter. We analyze the impact of radiative corrections coming from the electroweak sector of the standard model on the spectrum of the final products at th…
[Phys. Rev. D 82, 043512] Published Fri Aug 06, 2010”

Dark energy equation of state and cosmic topology. (arXiv:1008.0832v1 [astro-ph.CO]): ”

The immediate observational consequence of a non-trivial spatial topology of
the Universe is that an observer could potentially detect multiple images of
radiating sources. In particular, a non-trivial topology will generate pairs of
correlated circles of temperature fluctuations in the anisotropies maps of the
cosmic microwave background (CMB), the so-called circles-in-the-sky. In this
way, a detectable non-trivial spatial topology may be seen as an observable
attribute, which can be probed through the circles-in-the-sky for all locally
homogeneous and isotropic universes with no assumptions on the cosmological
dark energy (DE) equation of state (EOS) parameters. We show that the knowledge
of the spatial topology through the circles-in-the-sky offers an effective way
of reducing the degeneracies in the DE EOS parameters. We concretely illustrate
the topological role by assuming, as an exanple, a Poincar\'{e} dodecahedral
space topology and reanalyzing the constraints on the parameters of a specific
EOS which arise from the supernovae type Ia, baryon acoustic oscillations and
the CMB plus the statistical topological contribution.

Unified Dark Matter Scalar Field Models. (arXiv:1008.0614v1 [astro-ph.CO]): ”

In this work we analyze and review cosmological models in which the dynamics
of a single scalar field accounts for a unified description of the Dark Matter
and Dark Energy sectors, dubbed Unified Dark Matter (UDM) models. In this
framework, we consider the general Lagrangian of k-essence, which allows to
find solutions around which the scalar field describes the desired mixture of
Dark Matter and Dark Energy. We also discuss static and spherically symmetric
solutions of Einstein’s equations for a scalar field with non-canonical kinetic
term, in connection with galactic halo rotation curves

The propagator in polymer quantum field theory. (arXiv:1007.5500v1 [gr-qc]): ”

We study free scalar field theory on flat spacetime using a background
independent (polymer) quantization procedure. Specifically we compute the
propagator using a method that takes the energy spectrum and position matrix
elements of the harmonic oscillator as inputs. We obtain closed form results in
the infrared and ultraviolet regimes that give Lorentz invariance violating
dispersion relations, and show suppression of propagation at sufficiently high
energy.

Eternal Inflation with Liouville Cosmology. (arXiv:1007.5499v1 [hep-th]): ”

We present a concrete holographic realization of the eternal inflation and
its census taker in (1+1) dimensional Liouville gravity by applying the FRW/CFT
philosophy proposed by Freivogel, Sekino, Susskind and Yeh (FSSY). The dual
boundary theory is nothing but the old matrix model describing the
two-dimensional Liouville gravity coupled with minimal model matter fields. In
Liouville gravity, the flat Minkowski space or even the AdS space will decay
into the dS space, which is in stark contrast with higher dimensional theories,
but the spirit of the FSSY conjecture applies with only minimal modification.
We investigate the classical geometry as well as some correlation functions to
support our claim. We also study an analytic continuation to the time-like
Liouville theory to discuss possible applications in (1+3) dimensional
cosmology along with the original FSSY conjecture, where the boundary theory
involves the time-like Liouville theory. We show that the decay rate in the
$(1+3)$ dimension is more suppressed due to the quantum gravity correction of
the boundary theory.

Universo inflacionário: prelúdio


Como o tempo está curto, estou há algum tempo sem postar aqui no blog. Nesse post, pretendo dar início à discussão de um assunto muito interessante para aqueles interessados em cosmologia e física de (astro)partículas: o modelo de universo inflacionário. Como ponta pé inicial, deixo o seguinte trecho extremamente provocador do e-print http://arxiv.org/abs/hep-th/0402051, escrito por A. Linde, um dos pioneiros da Inflação:

[…]This competition goes in several different directions. First of all, we must try to implement inflation in realistic theories of fundamental interactions. But what do we mean by ‘realistic?’ In the absence of a direct confirmation of M/string theory and supergravity by high energy physics experiments (which may change when we start receiving data from the LHC), the definition of what is realistic becomes increasingly dependent on cosmology and the results of the cosmological observations. In particular, one may argue that those versions of the theory of all fundamental interactions that cannot describe inflation and the present stage of acceleration of the universe are disfavored by observations.[…]

Para aqueles que nunca tiveram contato com o modelo inflacionário, recomendo como leitura inicial http://en.wikipedia.org/wiki/Inflation_(cosmology). Ao longo da semana, escreverei mais sobre o assunto!

Até a próxima!