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Giacomo Rosati

Publications and source records attributed to Giacomo Rosati.

At least 37 records · Page 2Linked to original sources
arXiv2016

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".

gr-qc↗
arXiv2016

IceCube and GRB neutrinos propagating in quantum spacetime

Two recent publications have reported intriguing analyses, tentatively suggesting that some aspects of IceCube data might be manifestations of quantum-gravity-modified laws of propagation for neutrinos. We here propose a strategy of data analysis which has the advantage of being applicable to several alternative possibilities for the laws of propagation of neutrinos in a quantum spacetime. In all scenarios here of interest one should find a correlation between the energy of an observed neutrino and the difference between the time of observation of that neutrino and the trigger time of a GRB. We select accordingly some GRB-neutrino candidates among IceCube events, and our data analysis finds a rather strong such correlation. This sort of studies naturally lends itself to the introduction of a "false alarm probability", which for our analysis we estimate conservatively to be of 1%. We therefore argue that our findings should motivate a vigorous program of investigation following the strategy here advocated.

gr-qc↗
arXiv2015

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.

gr-qc↗
arXiv2015

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.

hep-th↗
arXiv2015

Multi-particle systems in $κ$-Poincaré inspired by 2+1D gravity

Inspired by a Chern-Simons description of 2+1D gravity coupled to point particles we propose a new Lagrangian of a multiparticle system living in $κ$-Minkowski/$κ$-Poincaré spacetime. We derive the dynamics of interacting particles with $κ$-momentum space, alternative to the one proposed in the "principle of relative locality" literature. The model that we obtain takes into account of the nonlocal topological interactions between the particles, so that the effective multi-particle action is not a sum of their free actions. In this construction the locality of particle processes is naturally implemented, even for distant observers. In particular a particle process is characterized by a local deformed energy-momentum conservation law. The spacetime transformations are generated by total charges/generators for the composite particle system, and leave unaffected the locality of individual particle processes.

hep-th↗
arXiv2014

Generally covariant formulation of Relative Locality in curved spacetime

We construct a theory of particles moving in curved both momentum space and spacetime, being a generalization of Relative Locality. We find that in order to construct such theory, with desired symmetries, including the general coordinate invariance, we have to use non local position variables. It turns out that free particles move on geodesics and momentum dependent translations of Relative Locality are replaced with momentum dependent geodesic deviations.

gr-qc↗
arXiv2013

Relative Locality in Curved Space-time

In this paper we construct the action describing dynamics of the particle moving in curved spacetime, with a non-trivial momentum space geometry. Curved momentum space is the core feature of theories where relative locality effects are presents. So far aspects of nonlinearities in momentum space have been studied only for flat or constantly expanding (De Sitter) spacetimes, relying on the their maximally symmetric nature. The extension of curved momentum space frameworks to arbitrary spacetime geometries could be relevant for the opportunities to test Planck-scale curvature/deformation of particles momentum space. As a first example of this construction we describe the particle with kappa-Poincaré momentum space on a circular orbit in Schwarzschild spacetime, where the contributes of momentum space curvature turn out to be negligible. The analysis of this problem relies crucially on the solution of the soccer ball problem.

hep-th↗
arXiv2013

Predictive description of Planck-scale-induced spacetime fuzziness

Several approaches to the quantum-gravity problem predict that spacetime should be "fuzzy", but have been so far unable to provide a crisp physical characterization of this notion. An intuitive picture of spacetime fuzziness has been proposed on the basis of semi-heuristic arguments, and in particular involves an irreducible Planck-scale contribution to the uncertainty of the energy of a particle. These arguments also inspired a rather active phenomenological programme looking for blurring of images of distant astrophysical sources that would result from such energy uncertainties. We here report the first ever physical characterization of spacetime fuzziness derived constructively within a quantum picture of spacetime, the one provided by spacetime noncommutativity. Our results confirm earlier heuristic arguments suggesting that spacetime fuzziness, while irrelevantly small on terrestrial scales, could be observably large for propagation of particles over cosmological distances. However, we find no Planck-scale-induced lower bound on the uncertainty of the energy of particles, and we observe that this changes how we should picture a quantum spacetime and also imposes a reanalysis of the associated phenomenology.

hep-th↗
arXiv2013

Gravity's weight on worldline fuzziness

We investigate a connection between recent results in 3D quantum gravity, providing an effective noncommutative-spacetime description, and some earlier heuristic descriptions of a quantum-gravity contribution to the fuzziness of the worldlines of particles. We show that 3D-gravity-inspired spacetime noncommutativity reflects some of the features suggested by previous heuristic arguments. Most notably, gravity-induced worldline fuzziness, while irrelevantly small on terrestrial scales, could be observably large for propagation of particles over cosmological distances.

gr-qc↗
arXiv2012

Relative locality in a quantum spacetime and the pregeometry of $κ$-Minkowski

We develop a new description of the much-studied $κ$-Minkowski noncommutative spacetime, centered on representing on a single Hilbert space not only the $κ$-Minkowski coordinates, but also the associated differential calculus and the $κ$-Poincaré symmetry generators. In this "pregeometric" representation the relevant operators act on the kinematical Hilbert space of the covariant formulation of quantum mechanics, which we argue is the natural framework for studying the implications of the step from commuting spacetime coordinates to the $κ$-Minkowski case, where the spatial coordinates do not commute with the time coordinate. The empowerment provided by this kinematical-Hilbert space representation allows us to give a crisp characterization of the "fuzziness" of $κ$-Minkowski spacetime, whose most striking aspect is a relativity of spacetime locality. We show that relative locality, which had been previously formulated exclusively in classical-spacetime setups, for a quantum spacetime takes the shape of a dependence of the fuzziness of a spacetime point on the distance at which an observer infers properties of the event that marks the point.

hep-th↗
arXiv2012

Deformed Lorentz symmetry and relative locality in a curved/expanding spacetime

The interest of part of the quantum-gravity community in the possibility of Planck-scale-deformed Lorentz symmetry is also fueled by the opportunities for testing the relevant scenarios with analyses, from a signal-propagation perspective, of observations of bursts of particles from cosmological distances. In this respect the fact that so far the implications of deformed Lorentz symmetry have been investigated only for flat (Minkowskian) spacetimes represents a very significant limitation, since for propagation over cosmological distances the curvature/expansion of spacetime is evidently tangible. We here provide a significant step toward filling this gap by exhibiting an explicit example of Planck-scale-deformed relativistic symmetries of a spacetime with constant rate of expansion (deSitterian). Technically we obtain the first ever example of a relativistic theory of worldlines of particles with 3 nontrivial relativistic invariants: a large speed scale ("speed-of-light scale"), a large distance scale (inverse of the "expansion-rate scale"), and a large momentum scale ("Planck scale"). We address some of the challenges that had obstructed success for previous attempts by exploiting the recent understanding of the connection between deformed Lorentz symmetry and relativity of spacetime locality. We also offer a preliminary analysis of the differences between the scenario we here propose and the most studied scenario for broken (rather than deformed) Lorentz symmetry in expanding spacetimes.

hep-th↗
arXiv2012

$κ$-Poincaré phase space: speed of massless particles and relativity of spacetime locality

The study of phase-space constructions based on the properties of the $κ$-Poincaré Hopf algebra has been a very active area, mostly because of its possible applications in the phenomenology of Planck-scale-induced momentum dependence of the speed of ultrarelativistic particles. We here summarize, with emphasis on the emerging relativity of spacetime locality, some results relevant for this research program that were recently reported in arXiv:1006.2126 (PhysRevLett106,071301) arXiv:1102.4637 (PhysLettB700,150) and arXiv:1107.1724 .

hep-th↗
arXiv2012

Taming nonlocality in theories with Planck-scale-deformed Lorentz symmetry

We report a general analysis of worldlines for theories with deformed relativistic symmetries and momentum dependence of the speed of photons. Our formalization is faithful to Einstein's program, with spacetime points viewed as an abstraction of physical events. The emerging picture imposes the renunciation of the idealization of absolutely coincident events, but is free from some pathologies which had been previously conjectured.

gr-qc↗
arXiv2011

Weakness of accelerator bounds on electron superluminality without a preferred frame

The reference laboratory bounds on superluminality of the electron are obtained from the absence of in-vacuo Cherenkov processes and the determinations of synchrotron radiated power for LEP electrons. It is usually assumed that these analyses establish the validity of a standard special-relativistic description of the electron with accuracy of at least a few parts in $10^{14}$, and in particular this is used to exclude electron superluminality with such an accuracy. We observe that these bounds rely crucially on the availability of a preferred frame. In-vacuo-Cherenkov processes are automatically forbidden in any theory with "deformed Lorentz symmetry", relativistic theories that, while different from Special Relativity, preserve the relativity of inertial frames. Determinations of the synchrotron radiated power can be used to constrain the possibility of Lorentz-symmetry deformation, but provide rather weak bounds, which in particular for electron superluminality we establish to afford us no more constraining power than for an accuracy of a few parts in $10^4$. We argue that this observation can have only a limited role in the ongoing effort of analysis of the anomaly tentatively reported by the OPERA collaboration, but we stress that it could provide a valuable case study for assessing the limitations of "indirect" tests of fundamental laws of physics.

hep-ph↗
arXiv2011

OPERA-reassessing data on the energy dependence of the speed of neutrinos

We offer a preliminary exploration of the two sides of the challenge provided by the recent OPERA data on superluminal neutrinos. On one side we stress that some aspects of this result are puzzling even from the perspective of the wild quantum-gravity literature, where arguments in favor of the possibility of superluminal propagation have been presented, but not considering the possibility of such a sizeable effect for neutrinos of such low energies. We feel this must encourage particularly severe scrutiny of the OPERA result. On the other side, we notice that the OPERA result is reasonably consistent with $μ$-neutrino-speed data previously obtained at FERMILAB, reported in papers of 2007 and 1979. And it is intriguing that these FERMILAB79 and FERMILAB07 results, when combined with the new OPERA result, in principle provide a window on $μ$-neutrino speeds at different energies broad enough to compare alternative phenomenological models. We test the discriminating power of such an approach by using as illustrative examples the case of special-relativistic tachyons, the case of "Coleman-Glashow-type" momentum-independent violations of the special-relativistic speed law, and the cases of linear and quadratic energy dependence of the speed of ultrarelativistic muon neutrinos. Even just using $μ$-neutrino data in the range from $\sim$ 3 GeVs to $\sim$ 200 GeVs the special-relativistic tachyon and the quadratic-dependence case are clearly disfavoured. The linear-dependence case gives a marginally consistent picture and the Coleman-Glashow scenario fits robustly the data. We also comment on Supernova 1987a and its relevance for consideration of other neutrino species, also in relation with some scenarios that appeared in the large-extra-dimension literature.

hep-ph↗
arXiv2011

Relative-locality distant observers and the phenomenology of momentum-space geometry

We study the translational invariance of the relative-locality framework proposed in arXiv:1101.0931, which had been previously established only for the case of a single interaction. We provide an explicit example of boundary conditions at endpoints of worldlines, which indeed ensures the desired translational invariance for processes involving several interactions, even when some of the interactions are causally connected (particle exchange). We illustrate the properties of the associated relativistic description of distant observers within the example of a $κ$-Poincaré-inspired momentum-space geometry, with de Sitter metric and parallel transport governed by a non-metric and torsionful connection. We find that in such a theory simultaneously-emitted massless particles do not reach simultaneously a distant detector, as expected in light of the findings of arXiv:1103.5626 on the implications of non-metric connections. We also show that the theory admits a free-particle limit, where the relative-locality results of arXiv:1102.4637 are reproduced. We establish that the torsion of the $κ$-Poincaré connection introduces a small (but observably-large) dependence of the time of detection, for simultaneously-emitted particles, on some properties of the interactions producing the particles at the source.

hep-th↗
arXiv2011

Speed of particles and a relativity of locality in $κ$-Minkowski quantum spacetime

The last decade of research on $κ$-Minkowski noncommutative spacetime has been strongly characterized by a controversy concerning the speed of propagation of massless particles. Most arguments suggested that this speed should depend on the momentum of the particle strongly enough to be of interest for some ongoing experimental studies. But the only explicit derivations of worldlines in $κ$-Minkowski predicted no momentum dependence for the speed of massless particles. We return to this controversy equipped with the recent understanding (arXiv:1006.2126, arXiv:1007.0718, arXiv:1008.2962, arXiv:1101.0931) that in some quantum spacetimes coincidences of events assessed by an observer who is distant from the events can be artifactual, and particularly Smolin's thesis (arXiv:1007.0718) that $κ$-Minkowski should be an example of such a spacetime. We therefore set up our investigation in such a way that we never rely on the assessment of coincidences of events by distant observers. This allows us to verify explicitly that in $κ$-Minkowski simultaneously-emitted massless particles of different momentum are detected at different times, and establish a linear dependence of the detection times on momentum.

hep-th↗