Papers by Gianluca Mandanici
Modern Physics Letters A, Mar 28, 2009
All the Doubly Special Relativity (DSR) models studied in literature so far involve a deformation... more All the Doubly Special Relativity (DSR) models studied in literature so far involve a deformation of the energy conservation rule that forces us to release the hypothesis of the additivity of the energy for composite systems. In view of the importance of the issue for a consistent formulation of a DSR statistical mechanics and a DSR thermodynamics, we show that DSR models preserving the usual (i.e. additive) energy conservation rule can be found. These models allow the construction of a DSR-covariant extensive energy. The implications of the analysis for the dynamics of DSR-covariant multiparticle systems are also briefly discussed.
Carolina Digital Repository (University of North Carolina at Chapel Hill), 2006
In several approaches to the quantum-gravity problem evidence has emerged of the validity of a "G... more In several approaches to the quantum-gravity problem evidence has emerged of the validity of a "GUP" (a Generalized position-momentum Uncertainty Principle) and/or a "MDR" (a modification of the energy-momentum dispersion relation), but very little is known about the implications of GUPs and MDRs for black-hole thermodynamics, another key topic for quantum-gravity research. We investigate an apparent link, already suggested in an earlier exploratory study involving two of us, between the possibility of a GUP and/or a MDR and the possibility of a log term in the area-entropy black-hole formula. We then obtain, from that same perspective, a modified relation between the mass of a black hole and its temperature, and we examine the validity of the "Generalized Second Law of black-hole thermodynamics" in theories with a GUP and/or a MDR. After an analysis of GUP-and MDR-modifications of the black-body radiation spectrum, we conclude the study with a description of the black-hole evaporation process.
International Journal of Modern Physics, Aug 20, 2004
We apply the Cornwall-Jackiw-Tomboulis (CJT) formalism to the scalar λϕ 4 theory in canonicalnonc... more We apply the Cornwall-Jackiw-Tomboulis (CJT) formalism to the scalar λϕ 4 theory in canonicalnoncommutative spacetime. We construct the CJT effective potential and the gap equation for general values of the noncommutative parameter θ µν. We observe that under the hypothesis of translational invariance, which is assumed in the effective potential construction, differently from the commutative case (θ µν = 0), the renormalizability of the gap equation is incompatible with the renormalizability of the effective potential. We argue that our result, is consistent with previous studies suggesting that a uniform ordered phase would be inconsistent with the infrared structure of canonical noncommutative theories.
Journal of Cosmology and Astroparticle Physics, Sep 16, 2003
The realization that forthcoming experimental studies, such as the ones planned for the GLAST spa... more The realization that forthcoming experimental studies, such as the ones planned for the GLAST space telescope, will be sensitive to Planck-scale deviations from Lorentz symmetry has increased interest in noncommutative spacetimes in which this type of effects is expected. We focus here on κ-Minkowski spacetime, a muchstudied example of Lie-algebra noncommutative spacetime, but our analysis appears to be applicable to a more general class of noncommutative spacetimes. A technical controversy which has significant implications for experimental testability is the one concerning the κ-Minkowski relation between group velocity and momentum. A large majority of studies adopted the relation v = dE(p)/dp, where E(p) is the κ-Minkowski dispersion relation, but recently some authors advocated alternative formulas. While in these previous studies the relation between group velocity and momentum was introduced through ad hoc formulas, we rely on a direct analysis of wave propagation in κ-Minkowski. Our results lead conclusively to the relation v = dE(p)/dp. We also show that the previous proposals of alternative velocity/momentum relations implicitly relied on an inconsistent implementation of functional calculus on κ-Minkowski and/or on an inconsistent description of spacetime translations.
Journal of High Energy Physics, Jan 19, 2004
We investigate some issues that are relevant for the derivation of experimental limits on the par... more We investigate some issues that are relevant for the derivation of experimental limits on the parameters of canonical noncommutative spacetimes. By analyzing a simple Wess-Zumino-type model in canonical noncommutative spacetime with soft supersymmetry breaking we explore the implications of ultraviolet supersymmetry on low-energy phenomenology. The fact that new physics in the ultraviolet can modify low-energy predictions affects significantly the derivation of limits on the noncommutativity parameters based on low-energy data. These are, in an appropriate sense here discussed, "conditional limits". We also find that some standard techniques for an effective low-energy description of theories with non-locality at short distance scales are only applicable in a regime where theories in canonical noncommutative spacetime lack any predictivity, because of the strong sensitivity to unknown UV physics. It appears useful to combine high-energy data, from astrophysics, with the more readily available low-energy data.
Journal of High Energy Physics, Sep 21, 2004
A quantum theory of noncommutative fields was recently proposed by Carmona, Cortez, Gamboa and Me... more A quantum theory of noncommutative fields was recently proposed by Carmona, Cortez, Gamboa and Mendez ([1]). The implications of the noncommutativity of the fields, intended as the requirements [φ, φ + ] = θδ 3 (x − x), [π, π + ] = Bδ 3 (x − x), were analyzed on the basis of an analogy with previous results on the so-called "noncommutative harmonic oscillator construction". Some departures from Lorentz symmetry turned out to play a key role in the emerging framework. We first consider the same hamiltonian proposed in [1], and we show that the theory can be analyzed straightforwardly within the framework of Heisenberg evolution equation without any need of making reference to the "noncommutative harmonic oscillator construction". We then consider a rather general class of alternative hamiltonians, and we observe that violations of Lorentz invariance are inevitably encountered. These violations must therefore be viewed as intrinsically associated with the proposed type of noncommutativity of fields, rather than as a consequence of a specific choice of hamiltonian.
arXiv (Cornell University), 2016
We modify the Chandrasekhar model of white dwarfs by introducing novel momentum-space features th... more We modify the Chandrasekhar model of white dwarfs by introducing novel momentum-space features that characterize the analysis of some quantum-spacetime scenarios. We find that the rather standard ultraviolet effects of spacetime quantization can only be significant in a regime where the Chandrasekhar model anyway lacks any contact with observations. But a new class of quantum-spacetime effects inspired by the mechanism of "ultraviolet/infrared mixing" could be relevant for white dwarfs whose mass is roughly half the mass of the Sun, some of which are described in the literature as "strange white dwarfs". We also offer a preliminary argument suggesting that Planck-scale (ultraviolet) effects could be significant in cases where ultra-high densities are present, even when the relevant star is still gigantic in Planck-length units.
arXiv (Cornell University), Dec 28, 2013
A map is discussed that connects, in 1+1 dimensions, Galilei's relativity to Einstein's special r... more A map is discussed that connects, in 1+1 dimensions, Galilei's relativity to Einstein's special relativity. By means of this map it is possible to derive special-relativistic formulas from the corresponding Galilean ones. Beyond being interesting on its own, this map is also significant with respect to a recent debate on the extension of relativistic symmetries to the Planck scale (especially in the framework of the so-called doubly special relativity). The map in fact provides an explicit example of how can be misleading to interpret a mathematical correspondence between two relativity schemes as an argument in favor of their physical equivalence.
International Journal of Modern Physics D, Feb 1, 2015
In the framework of the most-studied doubly special relativity models the use of the naive formul... more In the framework of the most-studied doubly special relativity models the use of the naive formula v = dE/dp has been argued to lead to inconsistencies connected to different rules of transformation, under boosts, of particles with the same energy but with different masses. In this paper we show that, at least in 1+1 dimensions, doubly special relativity can be formulated in such a way that the formula v = dE/dp is fully consistent with the invariance of the relative rest, easily fitting to the relativity principle. It is also argued that, always in 1+1d, is not necessary to renounce to the usual (commutative) Minkowski space-time endowed with energy-independent boost transformations. The compatibility of the approach with superluminal propagation, with linear addition rule for energy, and possible extensions to 3+1 dimensions are also discussed.
A map is discussed that connects, in 1+1 dimensions, Galilei's relativity to Einstein's s... more A map is discussed that connects, in 1+1 dimensions, Galilei's relativity to Einstein's special relativity. By means of this map it is possible to derive special-relativistic formulas from the corresponding Galilean ones. Beyond being interesting on its own, this map is also significant with respect to a recent debate on the extension of relativistic symmetries to the Planck scale (especially in the framework of the so-called doubly special relativity). The map in fact provides an explicit example of how can be misleading to interpret a mathematical correspondence between two relativity schemes as an argument in favor of their physical equivalence.
International Journal of Modern Physics D, 2015
In the framework of the most-studied doubly special relativity models the use of the naive formul... more In the framework of the most-studied doubly special relativity models the use of the naive formula v = dE/dp has been argued to lead to inconsistencies connected to different rules of transformation, under boosts, of particles with the same energy but with different masses. In this paper, we show that, at least in 1 + 1 dimensions, doubly special relativity can be formulated in such a way that the formula v = dE/dp is fully consistent with the invariance of the relative rest, easily fitting to the relativity principle. It is also argued that, always in 1 + 1 dimensions, is not necessary to renounce to the usual (commutative) Minkowski spacetime endowed with energy-independent boost transformations. The compatibility of the approach with superluminal propagation, with linear addition rule for energy, and possible extensions to 3 + 1 dimensions are also discussed.
International Journal of Modern Physics D, 2012
We modify the Chandrasekhar model of white dwarfs by introducing some of the momentum-space featu... more We modify the Chandrasekhar model of white dwarfs by introducing some of the momentum-space features which have been considered in the quantum-gravity literature. We find that when the new effects are confined to high energies, one only finds significant corrections to the Chandrasekhar model in regimes where the model anyway lacks any contact with observations. But these high-energy effects could play an important role in cases where ultra-high densities are present, even when the relevant star is still gigantic in Planck-length units. If the effects are not confined to high energies, as a result of "ultraviolet/infrared mixing", there could be significant implications for white dwarfs whose mass is roughly half the mass of the Sun, some of which are described in the literature as "strange white dwarfs".
Journal of High Energy Physics, 2004
A quantum theory of noncommutative fields was recently proposed by Carmona, Cortez, Gamboa and Me... more A quantum theory of noncommutative fields was recently proposed by Carmona, Cortez, Gamboa and Mendez (hep-th/0301248). The implications of the noncommutativity of the fields, intended as the requirements [φ, φ + ] = θδ 3 (x − x ′), [π, π + ] = Bδ 3 (x − x ′), were analyzed on the basis of an analogy with previous results on the so-called "noncommutative harmonic oscillator construction". Some departures from Lorentz symmetry turned out to play a key role in the emerging framework. We first consider the same hamiltonian proposed in hep-th/0301248, and we show that the theory can be analyzed straightforwardly within the framework of Heisenberg evolution equation without any need of making reference to the "noncommutative harmonic oscillator construction". We then consider a rather general class of alternative hamiltonians, and we observe that violations of Lorentz invariance are inevitably encountered. These violations must therefore be viewed as intrinsically associated with the proposed type of noncommutativity of fields, rather than as a consequence of a specific choice of Hamiltonian.
Journal of High Energy Physics, 2004
Modern Physics Letters A, 2009
All the Doubly Special Relativity (DSR) models studied in literature so far involve a deformation... more All the Doubly Special Relativity (DSR) models studied in literature so far involve a deformation of the energy conservation rule that forces us to release the hypothesis of the additivity of the energy for composite systems. In view of the importance of the issue for a consistent formulation of a DSR statistical mechanics and a DSR thermodynamics, we show that DSR models preserving the usual (i.e. additive) energy conservation rule can be found. These models allow the construction of a DSR-covariant extensive energy. The implications of the analysis for the dynamics of DSR-covariant multiparticle systems are also briefly discussed.
Journal of Cosmology and Astroparticle Physics, 2003
The realization that forthcoming experimental studies, such as the ones planned for the GLAST spa... more The realization that forthcoming experimental studies, such as the ones planned for the GLAST space telescope, will be sensitive to Planck-scale deviations from Lorentz symmetry has increased interest in noncommutative spacetimes in which this type of effects is expected. We focus here on κ-Minkowski spacetime, a muchstudied example of Lie-algebra noncommutative spacetime, but our analysis appears to be applicable to a more general class of noncommutative spacetimes. A technical controversy which has significant implications for experimental testability is the one concerning the κ-Minkowski relation between group velocity and momentum. A large majority of studies adopted the relation v = dE(p)/dp, where E(p) is the κ-Minkowski dispersion relation, but recently some authors advocated alternative formulas. While in these previous studies the relation between group velocity and momentum was introduced through ad hoc formulas, we rely on a direct analysis of wave propagation in κ-Minkowski. Our results lead conclusively to the relation v = dE(p)/dp. We also show that the previous proposals of alternative velocity/momentum relations implicitly relied on an inconsistent implementation of functional calculus on κ-Minkowski and/or on an inconsistent description of spacetime translations.
Journal of Cosmology and Astroparticle Physics, 2010
Several recent studies have considered the implications for astrophysics and cosmology of some po... more Several recent studies have considered the implications for astrophysics and cosmology of some possible nonclassical properties of spacetime at the Planck scale. The new effects, such as a Planck-scale-modified energy-momentum (dispersion) relation, are often inferred from the analysis of some quantum versions of Minkowski spacetime, and therefore the relevant estimates depend heavily on the assumption that there could not be significant interplay between Planck-scale and curvature effects. We here scrutinize this assumption, using as guidance a quantum version of de Sitter spacetime with known Inönü-Wigner contraction to a quantum Minkowski spacetime. And we show that, contrary to common (but unsupported) beliefs, the interplay between Planckscale and curvature effects can be significant. Within our illustrative example, in the Minkowski limit the quantum-geometry deformation parameter is indeed given by the Planck scale, while in the de Sitter picture the parameter of quantization of geometry depends both on the Planck scale and the curvature scalar. For the much-studied case of Planck-scale effects that intervene in the observation of gamma-ray bursts we can estimate the implications of "quantum spacetime curvature" within robust simplifying assumptions. For cosmology at the present stage of the development of the relevant mathematics one cannot go beyond semiheuristic reasoning, and we here propose a candidate approximate description of a quantum FRW geometry, obtained by patching together pieces (with different spacetime curvature) of our quantum de Sitter. This semiheuristic picture, in spite of its limitations, provides rather robust evidence that in the early Universe the interplay between Planck-scale and curvature effects could have been particularly significant.
International Journal of Modern Physics A, 2005
Investigations of the possibility that some novel "quantum" properties of space–time mi... more Investigations of the possibility that some novel "quantum" properties of space–time might induce a Planck-scale modification of the energy/momentum dispersion relation focused at first on scenarios with Planck-scale violations of Lorentz symmetry, with an associated reduced n-parameter (n<6) rotation-boost symmetry group. More recently several studies have also considered the possibility of a "doubly special relativity," in which the modification of the dispersion relation emerges from a framework with both the Planck scale and the speed-of-light scale as characteristic scales of a 6-parameter group of rotation-boost symmetry transformations (a deformation of the Lorentz transformations). For the schemes with broken Lorentz symmetry at the Planck scale there is a large literature on the derivation of experimental limits. Here we show that the analysis of the experimental limits could be significantly different in a doubly-special-relativity framework. We find...
Classical and Quantum Gravity, 2006
In several approaches to the quantum-gravity problem evidence has emerged of the validity of a "G... more In several approaches to the quantum-gravity problem evidence has emerged of the validity of a "GUP" (a Generalized position-momentum Uncertainty Principle) and/or a "MDR" (a modification of the energy-momentum dispersion relation), but very little is known about the implications of GUPs and MDRs for black-hole thermodynamics, another key topic for quantum-gravity research. We investigate an apparent link, already suggested in an earlier exploratory study involving two of us, between the possibility of a GUP and/or a MDR and the possibility of a log term in the area-entropy black-hole formula. We then obtain, from that same perspective, a modified relation between the mass of a black hole and its temperature, and we examine the validity of the "Generalized Second Law of black-hole thermodynamics" in theories with a GUP and/or a MDR. After an analysis of GUP-and MDR-modifications of the black-body radiation spectrum, we conclude the study with a description of the black-hole evaporation process.
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Papers by Gianluca Mandanici