arXiv subjects

Euro Spallucci

Publications and source records attributed to Euro Spallucci.

At least 37 records · Page 2Linked to original sources

arXiv2014

Holographic screens in ultraviolet self-complete quantum gravity

In this paper we study the geometry and the thermodynamics of a holographic screen in the framework of the ultraviolet self-complete quantum gravity. To achieve this goal we construct a new static, neutral, non-rotating black hole metric, whose outer (event) horizon coincides with the surface of the screen. The space-time admits an extremal configuration corresponding to the minimal holographic screen and having both mass and radius equalling the Planck units. We identify this object as the space-time fundamental building block, whose interior is physically unaccessible and cannot be probed even during the Hawking evaporation terminal phase. In agreement with the holographic principle, relevant processes take place on the screen surface. The area quantization leads to a discrete mass spectrum. An analysis of the entropy shows that the minimal holographic screen can store only one byte of information while in the thermodynamic limit the area law is corrected by a logarithmic term.

hep-th↗

arXiv2014

Goethe's Faust and the Minimal Action Principle: a possible Universal message

This short note is devoted to non-proficient in physics. Its purpose is that of proposing a possible universal connection between the definition of Action given by Goethe in his ``Faust'' tragic play and the Hamilton's Principle of the Minimal Action. This Principle is one of the most general ways of formulating the dynamics of a physical system both in classical and in quantum physics. The recent discovery of the long time searched Higgs particle may be seen as the most spectacular successful confirmation of the Standard Model formalism based on the Minimal Action Principle. Supported by this experimental confirmation, we propose a possible general meaning of the Principle, inspired by the Goethe's ``Faust'' tragic play.

physics.pop-ph↗

arXiv2014

The Abelian Higgs model and a minimal length in an un-particle scenario

We consider both the Abelian Higgs model and the impact of a minimal length in the un-particle sector. It is shown that even if the Higgs field takes a non-vanishing v.e.v., gauge interaction keeps its long range character leading to an effective gauge symmetry restoration. The effect of a quantum gravity induced minimal length on a physical observable is then estimated by using a physically-based alternative to the usual Wilson loop approach. Interestingly, we obtain an ultraviolet finite interaction energy described by a confluent hyper-geometric function, which shows a remarkable richness of behavior.

hep-th↗

arXiv2013

The final stage of gravitationally collapsed thick matter layers

In the presence of a minimal length physical objects cannot collapse to an infinite density, singular, matter point. In this note we consider the possible final stage of the gravitational collapse of "thick" matter layers. The energy momentum tensor we choose to model these shell-like objects is a proper modification of the source for "non-commutative geometry inspired", regular black holes. By using higher momenta of Gaussian distribution to localize matter at finite distance from the origin, we obtain new solutions of the Einstein's equation which smoothly interpolates between Minkowski geometry near the center of the shell and Schwarzschild spacetime far away from the matter layer. The metric is curvature singularity free. Black hole type solutions exist only for "heavy" shells, i.e. $M\ge M_{e}$, where $M_{e}$ is the mass of the extremal configuration. We determine the Hawking temperature and a modified Area Law taking into account the extended nature of the source.

gr-qc↗

arXiv2013

Maxwell's equal area law and the Hawking-Page phase transition

In this paper we study the phases of a Schwarzschild black hole in the Anti deSitter background geometry. Exploiting fluid/gravity duality we construct the Maxwell equal area isotherm T=T* in the temperature-entropy plane, in order to eliminate negative heat capacity black hole configurations. The construction we present here is reminiscent of the isobar cut in the pressure-volume plane which eliminates un-physical part of the Van der Walls curves below the critical temperature. Our construction also modifies the Hawking-Page phase transition. Stable black holes are formed at the temperature T > T*, while pure radiation persists for T< T*. T* turns out to be below the standard Hawking-Page temperature and there are no unstable black holes as in the usual scenario. Also, we show that in order to reproduce the correct black hole entropy S=A/4, one has to write a black hole equation of state, i.e. P=P(V), in terms of the geometrical volume V=4πr^3/3.

hep-th↗

arXiv2013

Why the length of a quantum string cannot be Lorentz contracted

We propose a quantum gravity-extended form of the classical length contraction law obtained in Special Relativity. More specifically, the framework of our discussion is the UV self-complete theory of quantum gravity. Against this background, we show how our results are consistent with, i) the generalised form of the Uncertainty Principle (GUP), ii) the so called hoop-conjecture which we interpret, presently, as the saturation of a Lorentz boost by the formation of a black hole in a two-body scattering, and iii) the intriguing notion of "classicalization" of trans-Planckian physics. Pushing these ideas to their logical conclusion, we argue that there is a physical limit to the Lorentz contraction rule in the form of some minimal universal length determined by quantum gravity, say the Planck Length, or any of its current embodiments such as the string length, or the TeV quantum gravity length scale. In the latter case, we determine the \emph{critical boost} that separates the ordinary "particle phase," characterized by the Compton wavelength, from the "black hole phase", characterized by the effective Schwarzschild radius of the colliding system. Finally, with the "classicalization" of quantum gravity in mind, we comment on the remarkable identity, to our knowledge never noticed before, between three seemingly independent universal quantities, namely, a) the "string tension", b) the "linear energy density," or \emph{tension} that exists at the core of all Schwarzschild black holes, and c) the "superforce" i.e., the Planckian limit of the static electro-gravitational force and, presumably, the unification point of all fundamental forces.

hep-th↗

arXiv2013

Maxwell's equal area law for charged Anti-deSitter black holes

In this paper we present the construction of the Maxwell equal area law in the Hawking temperature graph for a charged black hole in Anti-deSitter background. We are able to find exact solution for the corresponding isotherm and entropies for "gaseous" (large) black holes and "liquid" (near-extremal) black holes. Isothermal construction removes the unphysical, negative heat capacity, regions. Furthermore, extremal black holes turn out to be dual to "un-shrinkable" molecules of Van der Waals real fluid, which may explain their thermodynamical stability.

hep-th↗

arXiv2013

Production and evaporation of Planck scale black holes at the LHC

We review the phenomenology of mini black holes at colliders in light of the latest data from the LHC. By improving the conventional production cross-section, we show that the current non-observation of black hole signals can be explained in terms of quantum gravity effects. In the most optimistic case, black hole production could take place at a scale slightly above the LHC design energy. We also analyse possible new signatures of quantum-corrected Planck-scale black holes: in contrast to the semiclassical scenario the emission would take place in terms of soft particles mostly on the brane.

hep-th↗

arXiv2012

Thermodynamical phases of a regular SAdS black hole

This paper studies the thermodynamical stability of regular BHs in AdS5 background. We investigate off-shell free energy of the system as a function of temperature for different values of a "coupling constant" L=4 theta/l^2, where the cosmological constant is Lambda = -3/l^2 and \sqrt{theta} is a "minimal length". The parameter L admits a critical value, L_{inf}=0.2, corresponding to the appearance of an inflexion point in the Hawking temperature. In the weak-coupling regime L < L_{inf}, there are first order phase transitions at different temperatures. Unlike the Hawking-Page case, at temperature 0\le T \le T_{min} the ground state is populated by "cold" near-extremal BHs instead of a pure radiation. On the other hand, for L \g L_{inf} only large, thermodynamically stable, BHs exist.

hep-th↗

arXiv2012

Gauge symmetry restoration in the un-particle vacuum

In this note we investigate the impact of some "new-physics", beyond the electro-weak Standard Model of elementary particles, on the Higgs vacuum. We consider both un-particle and quantum gravity induced effects. We find that even if the Higgs field takes a non-vanishing v.e.v., gauge interaction keeps its long range character leading to an effective gauge symmetry restoration. Next, by using a physically-based alternative to the usual Wilson loop approach, we examine the effect of a quantum gravity induced minimal length on a physical observable in the un-particle sector. As a consequence, we obtain an ultraviolet finite interaction energy described by a confluent hyper-geometric function. This result displays a marked qualitative departure from its standard counterpart.

hep-th↗

arXiv2012

Aspects of finite electrodynamics in D=3 dimensions

We study the impact of a minimal length on physical observables for a three-dimensional axionic electrodynamics. Our calculation is done within the framework of the gauge-invariant, but path-dependent, variables formalism which is alternative to the Wilson loop approach. Our result shows that the interaction energy contains a regularised Bessel function and a linear confining potential. This calculation involves no theta expansion at all. Once again, the present analysis displays the key role played by the new quantum of length.

hep-th↗

arXiv2012

Could any black holes be produced at the LHC?

We introduce analytical quantum gravity modifications of the production cross section for terascale black holes by employing an effective ultraviolet cut off $l$. We find the new cross sections approach the usual "black disk" form at high energy, while they differ significantly near the fundamental scale from the standard increase with respect to $s$. We show that the heretofore discontinuous step function used to represent the cross section threshold can realistically be modeled by two functions representing the incoming and final parton states in a high energy collision. The growth of the cross section with collision energy is thus a unique signature of $l$ and number of spatial dimensions $d$. Contrary to the classical black disk result, our cross section is able to explain why black holes might not be observable in LHC experiments while they could be still at the reach of ultra-high energy cosmic ray events.

hep-ph↗

arXiv2012

Black holes production in self-complete quantum gravity

A regular black hole model, which has been proposed by Hayward, is reconsidered in the framework of higher dimensional TeV unification and self-complete quantum gravity scenario (Dvali, Spallucci). We point out the "quantum" nature of these objects and compute their cross section production by taking into account the key role played by the existence of a "minimal length" l_0. We show as the threshold energy is related to l_0. We recover, in the high energy limit, the standard "black-disk" form of the cross section, while it vanishes, below threshold, faster than any power of the invariant mass-energy \sqrt{-s}.

hep-th↗

arXiv2011

Finite axionic electrodynamics from a new noncommutative approach

Using the gauge-invariant but path-dependent variables formalism, we compute the static quantum potential for noncommutative axionic electrodynamics (or axionic electrodynamics in the presence of a minimal length). Accordingly, we obtain an ultraviolet finite static potential which is the sum of a Yukawa-type and a linear potential, leading to the confinement of static charges. Interestingly, it should be noted that this calculation involves no theta expansion at all. The present result makes manifest the key role played by the new quantum of length in our analysis.

hep-th↗

arXiv2011

Regular black holes in UV self-complete quantum gravity

In this letter we investigate the role of regular (curvature singularity-free) black holes in the framework of UV self-complete quantum gravity. The existence of a minimal length, shielding the trans-Planckian regime to any physical probe, is self-consistently included into the black hole probe itself. In this way we obtain to slightly shift the barrier below the Planck Length, with the UV self-complete scenario self-consistently confirmed.

hep-th↗

arXiv2010

Un-spectral dimension and quantum spacetime phases

In this Letter, we propose a new scenario emerging from the conjectured presence of a minimal length $\ell$ in the spacetime fabric, on the one side, and the existence of a new scale invariant, continuous mass spectrum, of un-particles on the other side. We introduce the concept of \textit{un-spectral dimension} $\mathbb{D}_U$ of a $d$-dimensional, euclidean (quantum) spacetime, as the spectral dimension measured by an "un-particle" probe. We find a general expression for the un-spectral dimension $\mathbb{D}_U$ labelling different spacetime phases: a semi-classical phase, where ordinary spectral dimension gets contribution from the scaling dimension $d_U$ of the un-particle probe ; a critical "Planckian phase", where four-dimensional spacetime can be effectively considered two-dimensional when $d_U=1$; a "Trans-Planckian phase", which is accessible to un-particle probes only, where spacetime as we currently understand it looses its physical meaning.

hep-th↗

arXiv2010

Vector unparticle enhanced black holes: exact solutions and thermodynamics

Tensor and scalar unparticle couplings to matter have been shown to enhance gravitational interactions and provide corrections to the Schwarzschild metric and associated black hole structure. We derive an exact solution to the Einstein equations for vector unparticles, and conclusively demonstrate that these induce Riessner-Nordström (RN)-like solutions where the role of the "charge" is defined by a composite of unparticle phase space parameters. These black holes admit double-horizon structure, although unlike the RN metric these solutions have a minimum inner horizon value. In the extremal limit, the Hawking temperature is shown to vanish. As with the scalar/tensor case, the (outer) horizon is shown via entropy considerations to behave like a fractal surface of spectral dimension $d_H = 2\du$.

hep-ph↗

arXiv2010

Un-graviton corrections to the Schwarzschild black hole

We introduce an effective action smoothly extending the standard Einstein-Hilbert action to include un-gravity effects. The improved field equations are solved for the un-graviton corrected Schwarzschild geometry reproducing the Mureika result. This is an important test to confirm the original ``guess'' of the form of the Un-Schwarzschild metric. Instead of working in the weak field approximation and ``dressing'' the Newtonian potential with un-gravitons, we solve the ``effective Einstein equations'' including all order un-gravity effects. An unexpected ``bonus'' of accounting un-gravity effects is the fractalisation of the event horizon. In the un-gravity dominated regime the event horizon thermodynamically behaves as fractal surface of dimensionality twice the scale dimension d_U.

hep-ph↗