Publications (200)892.57 Total impact
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ABSTRACT: Finsler geometry is a well known generalization of Riemannian geometry which allows to account for a possibly non trivial structure of the space of configurations of relativistic particles. We here establish a link between Finsler geometry and the sort of models with curved momentum space and DSRrelativistic symmetries which have been recently of interest in the quantumgravity literature. We use as case study the muchstudied scenario which is inspired by the $\kappa$Poincar\'e quantum group, and show that the relevant deformation of relativistic symmetries can be implemented within a Finsler geometry.07/2014; 
Article: Misleading inferences from discretization of empty spacetime: Snydernoncommutativity case study
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ABSTRACT: Alternative approaches to the study of the quantumgravity problem are handling the role of spacetime very differently. Some are focusing on the analysis of one or another novel formulation of "empty spacetime", postponing to later stages the introduction of particles and fields, while other approaches assume that spacetime should only be an emergent entity. We here argue that recent progress in the covariant formulation of quantum mechanics suggests that empty spacetime is not physically meaningful. We illustrate our general thesis in the specific context of the noncommutative Snyder spacetime, which is also of some intrinsic interest, since hundreds of studies were devoted to its analysis. We show that empty Snyder spacetime, described in terms of a suitable kinematical Hilbert space, is discrete, but this is only a formal artifact: the discreteness leaves no trace on the observable properties of particles on the physical Hilbert space.04/2014; 
Article: Gravity in quantum mechanics
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ABSTRACT: Gravity and quantum mechanics tend to stay out of each other's way, but this might change as we devise new experiments to test the applicability of quantum theory to macroscopic systems and larger length scales.03/2014; 10(4).  [Show abstract] [Hide abstract]
ABSTRACT: Theories with a curved momentum space, which became recently of interest in the quantumgravity literature, can in general violate many apparently robust aspects of our current description of the laws of physics, including relativistic invariance, locality, causality and global momentum conservation. We here explore some aspects of the particularly severe pathologies arising in generic theories with curved momentum space for what concerns causality and momentum conservation. However, we also report results suggesting that when momentum space is maximally symmetric, and the theory is formulated (DSR)relativistically, with the associated relativity of spacetime locality, momentum is globally conserved and there is no violation of causality.01/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We adopt a framework where quantum gravity’s dynamical dimensional reduction of spacetime at short distances is described in terms of modified dispersion relations. We observe that by subjecting such models to a momentumspace diffeomorphism one obtains a “dual picture” with unmodified dispersion relations, but a modified measure of integration over momenta. We then find that the UV Hausdorff dimension of momentum space which can be inferred from this modified integration measure coincides with the shortdistance spectral dimension of spacetime. This result sheds light into why scaleinvariant fluctuations are obtained if the original model for two UV spectral dimensions is combined with Einstein gravity. By studying the properties of the inner product we derive the result that it is only in two energymomentum dimensions that microphysical vacuum fluctuations are scale invariant. This is true ignoring gravity, but then we find that if Einstein gravity is postulated in the original frame, in the dual picture gravity switches off, since all matter becomes conformally coupled. We argue that our findings imply that the following concepts are closely connected: scale invariance of vacuum quantum fluctuations, conformal invariance of the gravitational coupling, UV reduction to spectral dimension two in position space, and UV reduction to Hausdorff dimension two in energymomentum space.Physical Review D 11/2013; 88(10). · 4.69 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Several approaches to quantum gravity suggest that the standard description of spacetime as probed at lowenergy, with four dimensions, is replaced in the Planckian regime by a spacetime with a spectral dimension of two. The implications for relativistic symmetries can be momentous, and indeed the most tangible picture for "running" of the spectral dimension, found within HoravaLifschitz gravity, requires the breakdown of relativity of inertial frames. In this Letter we incorporate running spectral dimensions in a scenario that does not require the emergence of a preferred frame. We consider the best studied mechanism for deforming relativistic symmetries whilst preserving the relativity of inertial frames, based on a momentum space with curvature at the Planck scale. We show explicitly how running of the spectral dimension can be derived from these models.11/2013; 
Article: The measure matters
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ABSTRACT: We adopt a framework where quantumgravity's dynamical dimensional reduction of spacetime at short distances is described in terms of modified dispersion relations. We observe that by subjecting such models to a momentumspace diffeomorphism one obtains a "dual picture" with unmodified dispersion relations, but a modified measure of integration over momenta. We then find that the UV {\it Hausdorff} dimension of momentum space which can be inferred from this modified integration measure coincides with the shortdistance {\it spectral} dimension of spacetime. This result sheds light into why scaleinvariant fluctuations are obtained if the original model for two UV spectral dimensions is combined with Einstein gravity. By studying the properties of the inner product we derive the result that it is only in 2 energymomentum dimensions that microphysical vacuum fluctuations are scaleinvariant. This is true ignoring gravity, but then we find that if Einstein gravity is postulated in the original frame, in the dual picture gravity switches off, since all matter becomes conformally coupled. We argue that our findings imply that the following concepts are closely connected: scaleinvariance of vacuum quantum fluctuations, conformal invariance of the gravitational coupling, UV reduction to spectral dimension 2 in position space and UV reduction to Hausdorff dimension 2 in energymomentum space.09/2013;  [Show abstract] [Hide abstract]
ABSTRACT: Several arguments suggest that the Planck scale could be the characteristic scale of curvature of momentum space. As other recent studies we assume that the metric of momentum space determines the condition of onshellness while the momentumspace affine connection governs the form of the law of composition of momenta. We show that the possible choices of laws of composition of momenta are more numerous than the possible choices of affine connection on a momentum space. This motivates us to propose a new prescription for associating an affine connection to momentum composition, which we compare to the one most used in the recent literature. We find that the two prescriptions lead to the same picture of the socalled $\kappa$momentum space, with de Sitter metric and $\kappa$Poincar\'e connection. We also examine in greater detail than ever before the DSRrelativistic properties of $\kappa$momentum space, particularly in relation to its noncommutative law of composition of momenta. We then show that in the case of "proper de Sitter momentum space", with the de Sitter metric and its LeviCivita connection, the two prescriptions are inequivalent. Our novel prescription leads to a picture of proper de Sitter momentum space which is DSRrelativistic and is characterized by a commutative law of composition of momenta, a possibility for which no explicit curvedmomentumspace picture had been previously found. We argue that our construction provides a natural test case for the study of momentum spaces with commutative, and yet deformed, laws of composition of momenta. Moreover, it can serve as laboratory for the exploration of the properties of DSRrelativistic theories which are not connected to groupmanifold momentum spaces and Hopf algebras.07/2013;  [Show abstract] [Hide abstract]
ABSTRACT: In a Comment [S. Hossenfelder Phys. Rev. D 88, 028701 (2013)], Hossenfelder proposes a generalization of the results we reported in [Phys. Rev. D 84, 087702 (2011)] and argues that thermal fluctuations introduce incurable pathologies for the description of macroscopic bodies in the relativelocality framework. We here show that Hossenfelder’s analysis, while raising a very interesting point, is incomplete and leads to incorrect conclusions. Her estimate for the fluctuations did not take into account some contributions from the geometry of momentum space, which must be included at the relevant order of approximation. Using the full expression here derived, one finds that thermal fluctuations are not, in general, large for macroscopic bodies in the relativelocality framework. We find that such corrections can be unexpectedly large only for some choices of momentumspace geometry, and we comment on the possibility of developing a phenomenology suitable for possibly ruling out such geometries of momentum space.Physical review D: Particles and fields 07/2013; 88(2).  [Show abstract] [Hide abstract]
ABSTRACT: We reexamine a recently proposed scenario where the deformed dispersion relations associated with a flow of the spectral dimension to a UV value of 2 leads to a scaleinvariant spectrum of cosmological fluctuations, without the need for inflation. In that scenario Einstein gravity was assumed. The theory displays a wavelengthdependent speed of light but by transforming to a suitable "rainbow frame" this feature can be removed, at the expense of modifying gravity. We find that the ensuing rainbow gravity theory is such that gravity switches off at high energy (or at least leads to a universal conformal coupling). This explains why the fluctuations are scaleinvariant on all scales: there is no horizon scale as such. For dispersion relations that do not lead to exact scale invariance we find instead esoteric inflation in the rainbow frame. We argue that these results shed light on the behaviour of gravity under the phenomenon of dimensional reduction.Physical Review D 07/2013; 88(4). · 4.69 Impact Factor 
Article: QuantumSpacetime Phenomenology
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ABSTRACT: I review the current status of phenomenological programs inspired by quantumspacetime research. I stress in particular the significance of results establishing that certain data analyses provide sensitivity to effects introduced genuinely at the Planck scale. My main focus is on phenomenological programs that affect the directions taken by studies of quantumspacetime theories.Living Reviews in Relativity 06/2013; · 22.33 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Several approaches to the investigation of the quantumgravity problem have provided "theoretical evidence" of a role for the Planck scale in characterizing the geometry of momentum space. One of the main obstructions for a full exploitation of this scenario is the understanding of the role of the Planckscalecurved geometry of momentum space in the correlations between emission and detection times, the "travel times" for a particle to go from a given emitter to a given detector. These travel times appear to receive Planckscale corrections for which no standard interpretation is applicable, and the associated implications for spacetime locality gave rise to the notion of "relative locality" which is still in the early stages of investigation. We here show that these Planckscale corrections to travel times can be described as "dual redshift" (or "lateshift"): they are manifestations of momentumspace curvature of the same type already known for ordinary redshift produced by spacetime curvature. In turn we can identify the novel notion of "relative momentumspace locality" as a known but underappreciated feature associated to ordinary redshift produced by spacetime curvature, and this can be described in complete analogy with the relative spacetime locality that became of interest in the recent quantumgravity literature. We also briefly comment on how these findings may be relevant for an approach to the quantumgravity problem proposed by Max Born in 1938 and centered on Born duality.Classical and Quantum Gravity 05/2013; 30(23). · 3.56 Impact Factor 
Article: Dimensional reduction in the sky
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ABSTRACT: We explore the cosmological implications of a mechanism found in several approaches to quantumgravity, whereby the spectral dimension of spacetime runs from the standard value of 4 in the infrared (IR) to a smaller value in the ultraviolet (UV). Specifically, we invoke the picture where the phenomenon is associated with modified dispersion relations. With minimal assumptions, we find that UV behaviour leading to 2 spectral dimensions results in an exactly scaleinvariant spectrum of vacuum scalar and tensor fluctuations, regardless of the equation of state. The fluctuation production mechanism is analogous to the one known for varying speed of sound/light models and, unlike in inflation, the spectrum is already scaleinvariant before leaving the horizon, remaining so after freezein. In the light of Planck's recent results we also discuss scenarios that break exact scaleinvariance, such as the possibility that the spectral dimension runs down to a value slightly higher than 2, or runs down to 2 but with an extremely slow transient. We further show that the tensor to scalar ratio is fixed by the UV ratio between the speed of gravity and the speed of light. Not only does our model not require inflation, but at its most minimal it seems incompatible with it. In contrast, we find that running spectral dimensions can improve the outlook of the cyclic/ekpyrotic scenario, solving the main problems present in its simplest and most appealing realisations.Physical review D: Particles and fields 05/2013; 87(12).  [Show abstract] [Hide abstract]
ABSTRACT: We process the Fermi LAT data on GRB130427A using the Fermi Science Tools, and we summarize some of the key facts that render this observation truly remarkable, especially concerning the quality of information on highenergy emission by GRBs. We then exploit this richness for a search of spectral lags, of the type that has been recently of interest for its relevance in quantumspacetime research. We do find some evidence of systematic soft spectral lags: when confining the analysis to photons of energies greater than 5 GeV there is an early hard development of minibursts within this long burst. The effect turns out to be well characterized quantitatively by a linear dependence, within such a miniburst, of the detection time on energy. With the guidance of our findings for GRB130427A we can then recognize that some support for these features is noticeable also in earlier FermiLAT GRBs, particularly for the presence of hard minibursts whose onset is marked by the highestenergy photon observed for the GRB. A comparison of these features for GRBs at different redshifts provides some encouragement for a redshift dependence of the effects of the type expected for a quantumspacetime interpretation, but other aspects of the analysis appear to invite the interpretation as intrinsic properties of GRBs.05/2013;  [Show abstract] [Hide abstract]
ABSTRACT: Several approaches to the quantumgravity 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 semiheuristic arguments, and in particular involves an irreducible Planckscale 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 Planckscaleinduced 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.Physical review D: Particles and fields 04/2013; 87(8).  [Show abstract] [Hide abstract]
ABSTRACT: Over the last decade a growing number of quantumgravity researchers has been looking for opportunities for the first ever experimental evidence of a Plancklength quantum property of spacetime. These studies are usually based on the analysis of some candidate indirect implications of spacetime quantization, such as a possible curvature of momentum space. Some recent proposals have raised hope that we might also gain direct experimental access to quantum properties of spacetime, by finding evidence of limitations to the measurability of the centerofmass coordinates of some macroscopic bodies. However I here observe that the arguments that originally lead to speculating about spacetime quantization do not apply to the localization of the center of mass of a macroscopic body. And I also analyze some popular formalizations of the notion of quantum spacetime, finding that when the quantization of spacetime is Planckian for the constituent particles then for the composite macroscopic body the quantization of spacetime is much weaker than Planckian. These results show that finding evidence of spacetime quantization with studies of macroscopic bodies is extremely unlikely. And they also raise some conceptual challenges for theories of mechanics in quantum spacetime, in which for example free protons and free atoms should feel the effects of spacetime quantization differently.Physical Review Letters 04/2013; 111(10). · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: One of the primary goals of neutrino telescopes, such as IceCube, is the discovery of neutrinos emitted by gammaray bursts (GRBs). Another source of interest in the results obtained by these telescopes is their possible use for tests of the applicability of Einstein's Special Relativity to neutrinos, particularly with respect to modifications that lead to Lorentz invariance violation that have been conjectured by some models of quantum spacetime. We examine here the fascinating scenario in which these two aspects of neutrinotelescope physics require a combined analysis. We discuss how neutrinos that one would not associate to a GRB, when assuming a classical spacetime picture, may well be GRB neutrinos if the possibility that Lorentz invariance is broken at very high energies is taken into account. As an illustrative example we examine three IceCube high energy neutrinos that arrived hours before GRBs (but from the same direction) and we find that the available, IceCube data, while inconclusive, is compatible with a scenario in which one or two of these neutrinos were GRB neutrinos and their earlier arrival reflects Lorentz invariance violation. We outline how future analyses of neutrino data should be done in order to systematically test this possibility.03/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We use the example of the muchstudied κMinkowski noncommutative spacetime for illustrating a novel approach toward the analysis of the possible implications of spacetime noncommutativity. Our starting point is the proposal that spacetime noncommutativity is most naturally introduced within the manifestlycovariant formulation of quantum mechanics. This allows us to obtain a crisp characterization of the relativity of spacetime locality present in κMinkowski theories. And we also develop a novel description of how κMinkowski noncommutativity affects the fuzziness of worldlines.Journal of Physics Conference Series 02/2013; 410(1):2143.  [Show abstract] [Hide abstract]
ABSTRACT: Over the last decade there were significant advances in the understanding of quantum gravity coupled to point particles in 3D (2+1dimensional) spacetime. Most notably it is emerging that the theory can be effectively described as a theory of free particles on a momentum space with antideSitter geometry and with noncommutative spacetime coordinates of the type $[x^{\mu},x^{\nu}]=i \hbar \ell \varepsilon^{\mu\nu}_{\phantom{\mu\nu}\rho} x^{\rho}$. We here show that the recently proposed relativelocality curvedmomentumspace framework is ideally suited for accommodating these structures characteristic of 3D quantum gravity. Through this we obtain an intuitive characterization of the DSRdeformed Poincar\'e symmetries of 3D quantum gravity, and find that the associated relative spacetime locality is of the type producing dualgravity lensing.Classical and Quantum Gravity 10/2012; 30(6). · 3.56 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigate a connection between recent results in 3D quantum gravity, providing an effective noncommutativespacetime description, and some earlier heuristic descriptions of a quantumgravity contribution to the fuzziness of the worldlines of particles. We show that 3Dgravityinspired spacetime noncommutativity reflects some of the features suggested by previous heuristic arguments. Most notably, gravityinduced worldline fuzziness, while irrelevantly small on terrestrial scales, could be observably large for propagation of particles over cosmological distances.International Journal of Modern Physics D 07/2012; 21(11). · 1.03 Impact Factor
Publication Stats
6k  Citations  
892.57  Total Impact Points  
Top Journals
Institutions

2000–2014

Sapienza University of Rome
 Department of Physics
Roma, Latium, Italy


2012

Perimeter Institute for Theoretical Physics
Waterloo, Ontario, Canada


1992–2003

University of Naples Federico II
 Department of Physical Sciences
Napoli, Campania, Italy 
University of Massachusetts Boston
Boston, Massachusetts, United States


1999–2000

CERN
Genève, Geneva, Switzerland


1998–1999

Université de Neuchâtel
 Institut de physique (IPH)
Neuchâtel, NE, Switzerland


1995–1998

University of Oxford
 Department of Physics
Oxford, ENG, United Kingdom


1994–1995

Massachusetts Institute of Technology
 Center for Theoretical Physics
Cambridge, MA, United States


1992–1993

Boston University
 Department of Physics
Boston, MA, United States
