1,721,032 research outputs found
The Higgs mechanism in nonlocal field theory
Full text linkAbstract We provide an example of nonlocal scalar electrodynamics that allows the same Higgs mechanism so successful in local field theory. The nonlocal action is structured in order to have the same exact solutions and the same equations of motion for perturbations of the local theory, at any perturbative order. Therefore, the perturbative degrees of freedom that propagate in the unstable vacuum are reshuffled when the stable vacuum is replaced in the EoM, but their number does not change at any perturbative order, and their properties are the same like in the usual local theory. Finally, the theory is superrenormalizable or finite at quantum level
Super-renormalizable or finite Lee–Wick quantum gravity
No full textWe propose a class of multidimensional higher derivative theories of gravity without extra real degrees of freedom besides the graviton field. The propagator shows up the usual real graviton pole in k2=0 and extra complex conjugates poles that do not contribute to the absorptive part of the physical scattering amplitudes. Indeed, they may consistently be excluded from the asymptotic observable states of the theory making use of the Lee–Wick and Cutkosky, Landshoff, Olive and Polkinghorne prescription for the construction of a unitary S-matrix. Therefore, the spectrum consists of the graviton and short lived elementary unstable particles that we named “anti-gravitons” because of their repulsive contribution to the gravitational potential at short distance. However, another interpretation of the complex conjugate pairs is proposed based on the Calmet's suggestion, i.e. they could be understood as black hole precursors long established in the classical theory. Since the theory is CPT invariant, the conjugate complex of the micro black hole precursor can be interpreted as a white hole precursor consistently with the 't Hooft complementarity principle. It is proved that the quantum theory is super-renormalizable in even dimension, i.e. only a finite number of divergent diagrams survive, and finite in odd dimension. Furthermore, turning on a local potential of the Riemann tensor we can make the theory finite in any dimension. The singularity-free Newtonian gravitational potential is explicitly computed for a range of higher derivative theories. Finally, we propose a new super-renormalizable or finite Lee–Wick standard model of particle physics
Quantum interference in the Kerr spacetime
Full text linkThe gravitational induced interference is studied here in the framework of teleparallel gravity. We derive the gravitational phase difference and we apply the result to the case of a Kerr spacetime. Afterwards, we compute the fringe shifts in an interference experiment of particles and discuss how to increase their values by changing the given parameters that include the area in between the paths, the energy of the particles, the distance from the black hole, the mass, and the spin of the black hole. It turns out that it is more difficult to detect the fringe shifts for massless particles than for massive particles. As a further application, we show how the mass of the black hole and its angular momentum can be obtained from the measurement of the fringe shifts. Finally, we compare the phase difference derived in teleparallel gravity with a previous work in general relativity
Galactic Rotation Curves in Conformal Scalar-Tensor Gravity
No full textWe show quantitatively that an exact solution of conformal scalar-tensor gravity can explain very well the galactic rotation curves for a sample of 104 galaxies without the need for dark matter or other exotic modification of gravity. The metric is an overall rescaling of the Schwarzschild-de Sitter space-time as required by Weyl conformal invariance, which has to be spontaneously broken, and the velocity of the stars depends only on two fixed universal parameters. Using the Monte Carlo Markov Chain (MCMC) method, we make a fit of the observational rotation curves in order to get the mass-to-light ratio for each galaxy. Finally, we analytically compare our model with the modified Newtonian dynamics (MOND) and the metric skew tensor gravity (MSTG) showing that the three theories have a very different behavior at very large distances
Non-perturbative spectrum of non-local gravity
No full textWe investigate the non-perturbative degrees of freedom of a class of weakly non-local gravitational theories that have been proposed as an ultraviolet completion of general relativity. At the perturbative level, it is known that the degrees of freedom of non-local gravity are the same of the Einstein-Hilbert theory around any maximally symmetric spacetime. We prove that, at the non-perturbative level, the degrees of freedom are actually eight in four dimensions, contrary to what one might guess on the basis of the "infinite number of derivatives" present in the action. It is shown that six of these degrees of freedom do not propagate on Minkowski spacetime, but they might play a role at large scales on curved backgrounds. We also propose a criterion to select the form factor almost uniquely. (C) 2019 The Author(s). Published by Elsevier B.V
Geodesic incompleteness of some popular regular black holes
Full text linkThroughout the study of the geodesics of some popular spherically symmetric
regular black holes, we hereby prove that the analytically extended Hayward
black hole is geodetically incomplete. The simplest extension of the
Culetu-Simpson-Visser's non-analytic smooth black hole is also geodetically
incomplete, with the exception of the antipodal continuation of the radial
geodesics. However, the huge ambiguity in the extension of non analytic
spacetimes is tantamount of geodesic incompleteness and such spacetimes do not
solve the singularity issue unless at least all the extensions turn out to be
complete. Hence, we provide several mere modifications of such spacetimes in
order to make them geodetically complete in all possible extensions beyond r=0.Comment: New version widely extended in accordance with the correct and
stimulating suggestions of the referee. This version is conform to the one
published on PRD. 8 pages, 9 figure
Particle creation by loop black holes
No full textWe study the black hole particle production in a regular spacetime metric obtained in a minisuperspace approach to loop quantum gravity. In different previous papers the static solution was obtained and shown to be singularity-free and self-dual. In this paper expanding a previous study of the black hole dynamics we repeat the Hawking analysis which leads to a thermal flux of particles at the future infinity. The evaporation time is infinite and the unitarity is recovered due to the regularity of the spacetime and to the characteristic behavior of the surface gravity. © 2014 Springer Science+Business Media New York
Quantum avoidance of Gödel’s closed timelike curves
Full text linkAbstract In a large class of nonlocal as well as local higher derivative theories minimally coupled to the matter sector, we investigate the exactness of two different classes of homogeneous Gödel-type solutions, which may or may not allow closed time-like curves (CTC). Our analysis is limited to spacetimes solving the Einstein’s EoM, thus we can not exclude the presence of other Gödel-type solutions solving the EoM of local and nonlocal higher derivative theories but not the Einstein’s EoM. It turns out that the homogeneous Gödel spacetimes without CTC are basically exact solutions for all theories, while the metrics with CTC are not exact solutions of (super-)renormalizable local or nonlocal gravitational theories. Hence, the quantum renormalizability property excludes theories suffering of the Gödel’s causality violation. We also comment about nonlocal gravity non-minimally coupled to matter. In this class of theories, all the Gödel’s spacetimes, with or without CTC, are exact solutions at classical level. However, the quantum corrections, although perturbative, very likely spoil the exactness of such solutions. Therefore, we can state that the Gödel’s Universes with CTC and the super-renormalizability are mutually exclusive
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