325 research outputs found
In-vacuo-dispersion features for GRB neutrinos and photons
Over the last 15 years there has been considerable interest in the
possibility of quantum-gravity-induced in-vacuo dispersion, the possibility
that spacetime itself might behave essentially like a dispersive medium for
particle propagation. Two very recent studies have exposed what might be
in-vacuo dispersion features for GRB (gamma-ray-burst) neutrinos of energy in
the range of 100 TeV and for GRB photons with energy in the range of 10 GeV. We
here show that these two features are roughly compatible with a description
such that the same effects apply over 4 orders of magnitude in energy. We also
characterize quantitatively how rare it would be for such features to arise
accidentally, as a result of (still unknown) aspects of the mechanisms
producing photons at GRBs or as a result of background neutrinos accidentally
fitting the profile of a GRB neutrino affected by in-vacuo dispersion.Comment: 12 pages, latex. arXiv admin note: text overlap with arXiv:1609.0398
Quantum-gravity-induced dual lensing and IceCube neutrinos
Momentum-space curvature, which is expected in some approaches to the
quantum-gravity problem, can produce dual redshift, a feature which introduces
energy dependence of the travel times of ultrarelativistic particles, and dual
lensing, a feature which mainly affects the direction of observation of
particles. In our recent arXiv:1605.00496 we explored the possibility that dual
redshift might be relevant in the analysis of IceCube neutrinos, obtaining
results which are preliminarily encouraging. Here we explore the possibility
that also dual lensing might play a role in the analysis of IceCube neutrinos.
In doing so we also investigate issues which are of broader interest, such as
the possibility of estimating the contribution by background neutrinos and some
noteworthy differences between candidate "early neutrinos" and candidate "late
neutrinos".Comment: In this version V2 we give a definition of variation probability
which could be considered in alternative to the notion of variation
probability already introduced in version V1; both notions of variation
probability are contemplated in the data analysis. arXiv admin note: text
overlap with arXiv:1605.0049
Cyclic universe from Loop Quantum Gravity
We discuss how a cyclic model for the flat universe can be constructively
derived from Loop Quantum Gravity. This model has a lower bounce, at small
values of the scale factor, which shares many similarities with that of Loop
Quantum Cosmology. We find that quantum gravity corrections can be also
relevant at energy densities much smaller than the Planckian one and that they
can induce an upper bounce at large values of the scale factor.Comment: 4 pages, misprint correcte
Planck-scale-modified dispersion relations in FRW spacetime
In recent years Planck-scale modifications of the dispersion relation have
been attracting increasing interest also from the viewpoint of possible
applications in astrophysics and cosmology, where spacetime curvature cannot be
neglected. Nonetheless the interplay between Planck-scale effects and spacetime
curvature is still poorly understood, particularly in cases where curvature is
not constant. These challenges have been so far postponed by relying on an
ansatz, first introduced by Jacob and Piran. We here propose a general strategy
of analysis of the effects of modifications of dispersion relation in FRW
spacetimes, applicable both to cases where the relativistic equivalence of
frames is spoiled ("preferred-frame scenarios") and to the alternative
possibility of "DSR-relativistic theories", theories that are fully
relativistic but with relativistic laws deformed so that the modified
dispersion relation is observer independent. We show that the Jacob-Piran
ansatz implicitly assumes that spacetime translations are not affected by the
Planck-scale, while under rather general conditions the same Planck-scale
quantum-spacetime structures producing modifications of the dispersion relation
also affect translations. Through the explicit analysis of one of the effects
produced by modifications of the dispersion relation, an effect amounting to
Planck-scale corrections to travel times, we show that our concerns are not
merely conceptual but rather can have significant quantitative implications
Optimal quantum state discrimination via nested binary measurements
A method to compute the optimal success probability of discrimination of N
arbitrary quantum states is presented, based on the decomposition of any
N-outcome measurement into sequences of nested two-outcome ones. In this way
the optimization of the measurement operators can be carried out in successive
steps, optimizing first the binary measurements at the deepest nesting level
and then moving on to those at higher levels. We obtain an analytical
expression for the maximum success probability after the first optimization
step and examine its form for the specific case of N=3,4 states of a qubit. In
this case, at variance with previous proposals, we are able to provide a
compact expression for the success probability of any set of states, whose
numerical optimization is straightforward; the results thus obtained highlight
some lesser-known features of the discrimination problem.Comment: v2: added references to previous works closely related to Sec. II;
8+3 pages; 3 figure
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