arXiv subjects

E. Speranza

Publications and source records attributed to E. Speranza.

5 recordsLinked to original sources

arXiv2024

Double-graviton production from Standard Model plasma

The thermal plasma filling the early universe generated a stochastic gravitational wave background that peaks in the microwave frequency range today. If the graviton production rate is expressed as a series in a fine-structure constant, $α$, and the temperature over the Planck mass, $T^2_{ } / m_{\rm pl}^2$, then the lowest-order contributions come from single ($\sim αT^2_{ }/m_{\rm pl}^2$) and double ($\sim T^4_{ }/m_{\rm pl}^4$) graviton production via $2\to 2$ scatterings. We show that in the Standard Model, single-graviton production dominates if the maximal temperature is smaller than $4\times 10^{18}_{ }$ GeV. This justifies previous calculations which relied solely on single-graviton production. We mention Beyond the Standard Model scenarios in which the single and double-graviton contributions could be of comparable magnitudes. Finally, we elaborate on what these results imply for the range of applicability of General Relativity as an effective theory.

hep-ph↗

arXiv2022

QCD Phase Structure and Interactions at High Baryon Density: Continuation of BES Physics Program with CBM at FAIR

We advocate for an active US participation in the international collaboration of the CBM experiment that will allow the US nuclear physics program to build on its successful exploration of the QCD phase diagram, use the expertise gained at RHIC to make complementary measurements at FAIR, and contribute to achieving the scientific goals of the beam energy scan (BES) program.

nucl-ex↗

arXiv2018

Spin tensor and its role in non-equilibrium thermodynamics

It is shown that the description of a relativistic fluid at local thermodynamic equilibrium depends on the particular quantum stress-energy tensor operator chosen, e.g., the canonical or symmetrized Belinfante stress-energy tensor. We argue that the Belinfante tensor is not appropriate to describe a relativistic fluid whose macroscopic polarization relaxes slowly to thermodynamic equilibrium and that a spin tensor, like the canonical spin tensor, is required. As a consequence, the description of a polarized relativistic fluid involves an extension of relativistic hydrodynamics including a new antisymmetric rank-two tensor as a dynamical field. We show that the canonical and Belinfante tensors lead to different predictions for measurable quantities such as spectrum and polarization of particles produced in relativistic heavy-ion collisions.

hep-th↗

arXiv2018

Relativistic hydrodynamics with spin

A newly proposed framework of perfect-fluid relativistic hydrodynamics for particles with spin 1/2 is briefly reviewed. The hydrodynamic equations follow entirely from the conservation laws for energy, momentum, and angular momentum. The incorporation of the angular-momentum conservation requires that the spin polarization tensor is introduced. It plays a role of a Lagrange multiplier conjugated to the spin tensor. The space-time evolution of the spin polarization tensor depends on the specific form chosen for the spin tensor.

nucl-th↗

arXiv2007

Asymptotic probability density functions in turbulence

A formalism is presented to obtain closed evolution equations for asymptotic probability distribution functions of turbulence magnitudes. The formalism is derived for a generic evolution equation, so that the final result can be easily applied to rather general problems. Although the approximation involved cannot be ascertained a priori, we show that application of the formalism to well known problems gives the correct results.

physics.flu-dyn↗