44,250 research outputs found
GRBs and fundamental physics
Gamma-ray bursts (GRBs) are short and intense flashes at the cosmological
distances, which are the most luminous explosions in the Universe. The high
luminosities of GRBs make them detectable out to the edge of the visible
universe. So, they are unique tools to probe the properties of high-redshift
universe: including the cosmic expansion and dark energy, star formation rate,
the reionization epoch and the metal evolution of the Universe. First, they can
be used to constrain the history of cosmic acceleration and the evolution of
dark energy in a redshift range hardly achievable by other cosmological probes.
Second, long GRBs are believed to be formed by collapse of massive stars. So
they can be used to derive the high-redshift star formation rate, which can not
be probed by current observations. Moreover, the use of GRBs as cosmological
tools could unveil the reionization history and metal evolution of the
Universe, the intergalactic medium (IGM) properties and the nature of first
stars in the early universe. But beyond that, the GRB high-energy photons can
be applied to constrain Lorentz invariance violation (LIV) and to test
Einstein's Equivalence Principle (EEP). In this paper, we review the progress
on the GRB cosmology and fundamental physics probed by GRBs.Comment: 38 pages, 18 figures, Review based on ISSI workshop "Gamma-Ray
Bursts: a Tool to Explore the Young Universe" (2015, Beijing, China),
accepted for publication in Space Science Review
Cosmological Term and Fundamental Physics
A nonvanishing cosmological term in Einstein's equations implies a
nonvanishing spacetime curvature even in absence of any kind of matter. It
would, in consequence, affect many of the underlying kinematic tenets of
physical theory. The usual commutative spacetime translations of the Poincare'
group would be replaced by the mixed conformal translations of the de Sitter
group, leading to obvious alterations in elementary concepts such as time,
energy and momentum. Although negligible at small scales, such modifications
may come to have important consequences both in the large and for the
inflationary picture of the early Universe. A qualitative discussion is
presented which suggests deep changes in Hamiltonian, Quantum and Statistical
Mechanics. In the primeval universe as described by the standard cosmological
model, in particular, the equations of state of the matter sources could be
quite different from those usually introduced.Comment: RevTeX, 4 pages. Selected for Honorable Mention in the Annual Essay
Competition of the Gravity Research Foundation for the year 200
Exotic Acceleration Processes and Fundamental Physics
Gamma-ray bursts and ultra-high-energy cosmic rays provide an important
testing ground for fundamental physics. A simple-minded analysis of some
gamma-ray bursts would lead to a huge estimate of the overall energy emitted,
and this represents a potential challenge for modelling the bursts. Some cosmic
rays have been observed with extremely high energies, and it is not easy to
envision mechanisms for the acceleration of particles to such high energies.
Surprisingly some other aspects of the analysis of gamma-ray bursts and
ultra-high-energy cosmic rays, even before reaching a full understanding of the
mechanisms that generate them, can already be used to explore new ideas in
fundamental physics, particularly for what concerns the structure of spacetime
at short (Planckian) distance scales.Comment: 5 pages, LaTex; Brief overview of the contributions to the section
"Exotic Acceleration Processes and Fundamental Physics" of the Huntsville
Workshop monograph (proceedings) "Particle Acceleration in Astrophysical
Plasmas: Geospace and Beyond
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