arXiv subjects

D. Zappalà

Publications and source records attributed to D. Zappalà.

8 recordsLinked to original sources

arXiv2024

Spontaneous breaking of diffeomorphism invariance in conformally reduced quantum gravity

We study the spontaneous breaking of diffeomorphism invariance using the proper-time non-perturbative flow equation in quantum gravity. In particular, we analyze the structure of the UV critical manifold of conformally reduced Einstein-Hilbert theory and observe the occurrence of a non-trivial minimum for the conformal factor at Planckian energies. We argue that our result can be interpreted as the occurrence of a dynamically generated minimal length in quantum gravity.

gr-qc↗

arXiv2017

Impact of New Physics on the EW vacuum stability in a curved spacetime background

It has been recently shown that, contrary to an intuitive decoupling argument, the presence of new physics at very large energy scales (say around the Planck scale) can have a strong impact on the electroweak vacuum lifetime. In particular, the vacuum could be totally destabilized. This study was performed in a flat spacetime background, and it is important to extend the analysis to curved spacetime since these are Planckian-physics effects. It is generally expected that under these extreme conditions gravity should totally quench the formation of true vacuum bubbles, thus washing out the destabilizing effect of new physics. In this work we extend the analysis to curved spacetime and show that, although gravity pushes toward stabilization, the destabilizing effect of new physics is still (by far) the dominating one. In order to get model independent results, high energy new physics is parametrized in two different independent ways: as higher order operators in the Higgs field, or introducing new particles with very large masses. The destabilizing effect is observed in both cases, hinting at a general mechanism that does not depend on the parametrization details for new physics, thus maintaining the results obtained from the analysis performed in flat spacetime.

hep-ph↗

arXiv2011

A reanalysis of Finite Temperature SU(N) Gauge Theory

We revise the $SU(N_c)$, $N_c=3,4,6$, lattice data on pure gauge theories at finite temperature by means of a quasi-particle approach. In particular we focus on the relation between the quasi-particle effective mass and the order of the deconfinement transition, the scaling of the interaction measure with $N^2_c -1$, the role of gluon condensate, the screening mass.

hep-ph↗

arXiv2008

Time evolution of T_{μν} and the cosmological constant problem

We study the cosmic time evolution of an effective quantum field theory energy-momentum tensor T_{μν} and show that, as a consequence of the effective nature of the theory, the structure of T_{μν} is such that the vacuum energy decreases with time. We find that the zero point energy at present time is washed out by the cosmological evolution. The implications of this finding for the cosmological constant problem are investigated.

hep-ph↗

arXiv2006

Scaling of variables and the relation between noncommutative parameters in Noncommutative Quantum Mechanics

We consider Noncommutative Quantum Mechanics with phase space noncommutativity. In particular, we show that a scaling of variables leaves the noncommutative algebra invariant, so that only the self-consistent effective parameters of the model are physically relevant. We also discuss the recently proposed relation of direct proportionality between the noncommutative parameters, showing that it has a limited applicability.

hep-th↗

arXiv2005

Noncommutative Gravitational Quantum Well

We study noncommutative geometry at the Quantum Mechanics level by means of a model where noncommutativity of both configuration and momentum spaces is considered. We analyze how this model affects the problem of the two-dimensional gravitational quantum well and use the latest experimental results for the two lowest energy states of neutrons in the Earth's gravitational field to establish an upper bound on the fundamental momentum scale introduced by noncommutativity, namely $\sqrtη\lesssim1\ \mathrm{meV/c}$, a value that can be improved in the future by up to 3 orders of magnitude. We show that the configuration space noncommutativity has, in leading order, no effect on the problem. We also analyze some features introduced by the model, specially a correction to the presently accepted value of Planck's constant to 1 part in $10^{24}$.

hep-th↗

arXiv2004

On the direct CP violation parameter epsilon prime

We review different definitions of the $ε'$ parameter describing direct CP violation in neutral kaon decays, which was precisely measured in recent experiments, and point out the inconsistency of some of them due to a CPT constraint. The proper comparison of the experimental results to the theoretical computations is discussed.

hep-ph↗

arXiv2000

Towards an accurate determination of the critical exponents with the Renormalization Group flow equations

The determination of the critical exponents by means of the Exact Renormalizion Group approach is still a topic of debate. The general flow equation is by construction scheme independent, but the use of the truncated derivative expansion generates a model dependence in the determination of the universal quantities. We derive new nonperturbative flow equations for the one-component, $Z_2$ symmetric scalar field to the next-to-leading order of the derivative expansion by means of a class of proper time regulators. The critical exponents $η$, $ν$ and $ω$ for the Wilson-Fisher fixed point are computed by numerical integration of the flow equations, without resorting to polynomial truncations. We show that by reducing the width of the cut-off employed, the critical exponents become rapidly insensitive to the cut-off width and their values are in good agreement with the results of entirely different approaches.

hep-th↗