Arquivo da tag: artigos

Especiais de fim de ano

Todos sabem como é: fim de ano chegando implica em todos os meios de comunicação publicarem toneladas de retrospectivas e listas com os melhores ou mais importantes acontecimentos do ano. No meio científico não é diferente. Abaixo seguem algumas listas publicadas nas últimas semanas de 2010 relacionadas aos avanços da Física:

Vale a pena se perder nesses links. Caso encontre mais listas interessantes, farei um update desse post.

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

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

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!

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

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.