56 research outputs found
Back-reaction effects in acoustic black holes
Acoustic black holes are very interesting non-gravitational objects which can
be described by the geometrical formalism of General Relativity. These models
can be useful to experimentally test effects otherwise undetectable, as for
example the Hawking radiation. The back-reaction effects on the background
quantities induced by the analogue Hawking radiation could be the key to
indirectly observe it. We briefly show how this analogy works and derive the
backreaction equations for the linearized quantum fluctuations in the
background of an acoustic black hole. A first order in hbar solution is given
in the near horizon region. It indicates that acoustic black holes, unlike
Schwarzschild ones, get cooler as they radiate phonons. They show remarkable
analogies with near-extremal Reissner-Nordstrom black holes.Comment: 10 pages, 1 figure; Talk given at the conference ``Constrained
Dynamics and Quantum Gravity (QG05)", Cala Gonone (Italy), September 200
The Stabilized Poincare-Heisenberg algebra: a Clifford algebra viewpoint
The stabilized Poincare-Heisenberg algebra (SPHA) is the Lie algebra of
quantum relativistic kinematics generated by fifteen generators. It is obtained
from imposing stability conditions after attempting to combine the Lie algebras
of quantum mechanics and relativity which by themselves are stable, however not
when combined. In this paper we show how the sixteen dimensional Clifford
algebra CL(1,3) can be used to generate the SPHA. The Clifford algebra path to
the SPHA avoids the traditional stability considerations, relying instead on
the fact that CL(1,3) is a semi-simple algebra and therefore stable. It is
therefore conceptually easier and more straightforward to work with a Clifford
algebra. The Clifford algebra path suggests the next evolutionary step toward a
theory of physics at the interface of GR and QM might be to depart from working
in space-time and instead to work in space-time-momentum.Comment: 14 page
Interpreting doubly special relativity as a modified theory of measurement
In this article we develop a physical interpretation for the deformed
(doubly) special relativity theories (DSRs), based on a modification of the
theory of measurement in special relativity. We suggest that it is useful to
regard the DSRs as reflecting the manner in which quantum gravity effects
induce Planck-suppressed distortions in the measurement of the "true" energy
and momentum. This interpretation provides a framework for the DSRs that is
manifestly consistent, non-trivial, and in principle falsifiable. However, it
does so at the cost of demoting such theories from the level of "fundamental"
physics to the level of phenomenological models -- models that should in
principle be derivable from whatever theory of quantum gravity one ultimately
chooses to adopt.Comment: 18 pages, plain LaTeX2
Generalized commutation relations and Non linear momenta theories, a close relationship
A revision of generalized commutation relations is performed, besides a
description of Non linear momenta realization included in some DSR theories. It
is shown that these propositions are closely related, specially we focus on
Magueijo Smolin momenta and Kempf et al. and L.N. Chang generalized
commutators. Due to this, a new algebra arises with its own features that is
also analyzed.Comment: accepted version in IJMP
Acoustic black holes for relativistic fluids
We derive a new acoustic black hole metric from the Abelian Higgs model. In
the non-relativistic limit, while the Abelian Higgs model becomes the
Ginzburg-Landau model, the metric reduces to an ordinary Unruh type. We
investigate the possibility of using (type I and II) superconductors as the
acoustic black holes. We propose to realize experimental acoustic black holes
by using spiral vortices solutions from the Navier-stokes equation in the
non-relativistic classical fluids.Comment: 16 pages. typos corrected, contents expande
The cosmological constant from the QCD Veneziano ghost
We suggest that the solution to the cosmological vacuum energy puzzle is
linked to the infrared sector of the effective theory of gravity interacting
with standard model fields, with QCD fields specifically. We work in the
framework of low energy quantum gravity as an effective field theory. In
particular, we compute the vacuum energy in terms of QCD parameters and the
Hubble constant such that the vacuum energy is \epsilon_{vac} \sim H \cdot
m_q\la\bar{q}q\ra /m_{\eta'} \sim (3.6\cdot 10^{-3} \text{eV})^4, which is
amazingly close to the observed value today. The QCD ghost (responsible for the
solution of the problem) plays a crucial r\^ole in the computation of
the vacuum energy, because the ghost's properties at very large but finite
distances slightly deviate (as \sim H / \Lqcd ) from their infinite volume
Minkowski values. Another important prediction of this framework states that
the vacuum energy owes its existence to the asymmetry of the cosmos. Indeed,
this effect is a direct consequence of the embedding of our Universe on a
non-trivial manifold such as a torus with (slightly) different linear sizes.
Such a violation of cosmological isotropy is apparently indeed supported by
WMAP, and will be confirmed (or ruled out) by future PLANCK data.Comment: 4 pages, uses revtex4, v2 as publishe
The Theory of a Quantum Noncanonical Field in Curved Spacetimes
Much attention has been recently devoted to the possibility that quantum
gravity effects could lead to departures from Special Relativity in the form of
a deformed Poincar\`e algebra. These proposals go generically under the name of
Doubly or Deformed Special Relativity (DSR). In this article we further explore
a recently proposed class of quantum field theories, involving noncanonically
commuting complex scalar fields, which have been shown to entail a DSR-like
symmetry. An open issue for such theories is whether the DSR-like symmetry has
to be taken as a physically relevant symmetry, or if in fact the "true"
symmetries of the theory are just rotations and translations while boost
invariance has to be considered broken. We analyze here this issue by extending
the known results to curved spacetime under both of the previous assumptions.
We show that if the symmetry of the free theory is taken to be a DSR-like
realization of the Poincar\'e symmetry, then it is not possible to render such
a symmetry a gauge symmetry of the curved physical spacetime. However, it is
possible to introduce an auxiliary spacetime which allows to describe the
theory as a standard quantum field theory in curved spacetime. Alternatively,
taking the point of view that the noncanonical commutation of the fields
actually implies a breakdown of boost invariance, the physical spacetime
manifold has to be foliated in surfaces of simultaneity and the field theory
can be coupled to gravity by making use of the ADM prescription.Comment: 9 pages, no figure
Kinematics of a relativistic particle with de Sitter momentum space
We discuss kinematical properties of a free relativistic particle with
deformed phase space in which momentum space is given by (a submanifold of) de
Sitter space. We provide a detailed derivation of the action, Hamiltonian
structure and equations of motion for such free particle. We study the action
of deformed relativistic symmetries on the phase space and derive explicit
formulas for the action of the deformed Poincare' group. Finally we provide a
discussion on parametrization of the particle worldlines stressing analogies
and differences with ordinary relativistic kinematics.Comment: RevTeX, 12 pages, no figure
Modified Dispersion Relations from the Renormalization Group of Gravity
We show that the running of gravitational couplings, together with a suitable
identification of the renormalization group scale can give rise to modified
dispersion relations for massive particles. This result seems to be compatible
with both the frameworks of effective field theory with Lorentz invariance
violation and deformed special relativity. The phenomenological consequences
depend on which of the frameworks is assumed. We discuss the nature and
strength of the available constraints for both cases and show that in the case
of Lorentz invariance violation, the theory would be strongly constrained.Comment: revtex4, 9 pages, updated to match published versio
Momentum Spectra for Dynamically Assisted Schwinger Pair Production
Recently the dynamically assisted Schwinger mechanism, i.e.,
electron-positron pair production from vacuum by a combination of laser pulses
with different time scales has been proposed. The corresponding results, which
suggest that the rate of produced pairs is significantly enhanced by dynamical
effects, are verified. Employing the framework of quantum kinetic theory
intrinsically enables us to additionally provide momentum space information on
the generated positron spectrum.Comment: 6 pages, 7 figure
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