2,085 research outputs found
Development of an internal restraint system for an integrated restraint-pressure suit system Report, 7 Jun. 1965 - 28 Jun. 1966
Internal restraint system, composed of liquid filled garment and separate auxiliary system, for integrated restraint pressure suit for acceleration protection and thermal transpor
Study of time lags in HETE-2 Gamma-Ray Bursts with redshift: search for astrophysical effects and Quantum Gravity signature
The study of time lags between spikes in Gamma-Ray Bursts light curves in
different energy bands as a function of redshift may lead to the detection of
effects due to Quantum Gravity. We present an analysis of 15 Gamma-Ray Bursts
with measured redshift, detected by the HETE-2 mission between 2001 and 2006 in
order to measure time lags related to astrophysical effects and search for
Quantum Gravity signature in the framework of an extra-dimension string model.
The use of photon-tagged data allows us to consider various energy ranges.
Systematic effects due to selection and cuts are evaluated. No significant
Quantum Gravity effect is detected from the study of the maxima of the light
curves and a lower limit at 95% Confidence Level on the Quantum Gravity scale
parameter of 3.2x10**15 GeV is set.Comment: 4 pages, 5 figures. v3: Error corrected in Eq. 1. Results updated.
Proceedings of the 30th ICRC, Merida, Mexico (2007
Constraints on Lorentz Invariance Violation using INTEGRAL/IBIS observations of GRB041219A
One of the experimental tests of Lorentz invariance violation is to measure
the helicity dependence of the propagation velocity of photons originating in
distant cosmological obejcts. Using a recent determination of the distance of
the Gamma-Ray Burst GRB 041219A, for which a high degree of polarization is
observed in the prompt emission, we are able to improve by 4 orders of
magnitude the existing constraint on Lorentz invariance violation, arising from
the phenomenon of vacuum birefringence.Comment: 5 pages, 3 figures, accepted for publication as a Rapid Communication
in Physical Review
Deformed Special Relativity as an effective theory of measurements on quantum gravitational backgrounds
In this article we elaborate on a recently proposed interpretation of DSR as
an effective measurement theory in the presence of non-negligible (albeit
small) quantum gravitational fluctuations. We provide several heuristic
arguments to explain how such a new theory can emerge and discuss the possible
observational consequences of this framework.Comment: 11 pages, no figure
Reality and causality in quantum gravity modified electrodynamics
We present a general description of the propagation properties of quantum
gravity modified electrodynamics characterized by constitutive relations up to
second order in the correction parameter. The effective description corresponds
to an electrodynamics in a dispersive and absorptive non-local medium, where
the Green functions and the refraction indices can be explicitly calculated.
The reality of the electromagnetic field together with the requirement of
causal propagation in a given referrence frame leads to restrictions in the
form of such refraction indices. In particular, absorption must be present in
all cases and, contrary to the usual assumption, it is the dominant aspect in
those effective models which exhibit linear effects in the correction parameter
not related to birefringence. In such a situation absorption is linear while
propagation is quadratical in the correction parameter.Comment: 15 pages, LaTex, minor changes to clarify some points, version
accepted for publicatio
Lorentz Invariance and the semiclassical approximation of loop quantum gravity
It is shown that the field equations derived from an effective interaction
hamiltonian for Maxwell and gravitational fields in the semiclassical
approximation of loop quantum gravity using rotational invariant states (such
as weave states) are Lorentz invariant. To derive this result, which is in
agreement with the observational evidence, we use the geometrical properties of
the electromagnetic field.Comment: 6 page
Preferred foliation effects in Quantum General Relativity
We investigate the infrared (IR) effects of Lorentz violating terms in the
gravitational sector using functional renormalization group methods similar to
Reuter and collaborators. The model we consider consists of pure quantum
gravity coupled to a preferred foliation, described effectively via a scalar
field with non-standard dynamics. We find that vanishing Lorentz violation is a
UV attractive fixed-point of this model in the local potential approximation.
Since larger truncations may lead to differing results, we study as a first
example effects of additional matter fields on the RG running of the Lorentz
violating term and provide a general argument why they are small.Comment: 12 pages, no figures, compatible with published versio
Sensitivity of Hawking radiation to superluminal dispersion relations
We analyze the Hawking radiation process due to collapsing configurations in
the presence of superluminal modifications of the dispersion relation. With
such superluminal dispersion relations, the horizon effectively becomes a
frequency-dependent concept. In particular, at every moment of the collapse,
there is a critical frequency above which no horizon is experienced. We show
that, as a consequence, the late-time radiation suffers strong modifications,
both quantitative and qualitative, compared to the standard Hawking picture.
Concretely, we show that the radiation spectrum becomes dependent on the
measuring time, on the surface gravities associated with different frequencies,
and on the critical frequency. Even if the critical frequency is well above the
Planck scale, important modifications still show up.Comment: 14 pages, 7 figures. Extensive paragraph added in conclusions to
clarify obtained result
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
- âŠ