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Giorgio Torrieri

Publications and source records attributed to Giorgio Torrieri.

At least 37 records · Page 2Linked to original sources
arXiv2025

Chiral oscillations in finite time quantum field theory

We demonstrate how chiral oscillations of a massive Dirac field can be described within quantum field theory using a finite-time interaction picture approach, where the mass term in the Lagrangian is treated as a perturbative coupling between massless fields of definite chirality. We derive the formula for chiral oscillations at the fourth order in the perturbative expansion, obtaining a result consistent with the formula derived by means of other methods. Furthermore, we illustrate how the perturbative framework of chiral oscillations can effectively describe production processes where an electron must exhibit both left chirality and positive helicity, as in decay $π^- \to e^- + {\bar ν}_e$. Finally, we argue that, in this perturbative view, chiral oscillations are also essential for detecting the decay products in such processes.

hep-ph↗
arXiv2025

What is "quantum" about quantum gravity?

Assuming the validity of the equivalence principle in the quantum regime, we argue that one of the assumptions of the usual definition of quantum mechanics, namely separation between the ``classical'' detector and the ``quantum'' system, must be relaxed. We argue, therefore, that if both the equivalence principle and quantum mechanics continue to survive experimental tests, that this favors ``epistemic'' interpretations of quantum mechanics (where formalism is built around relations between observables) over ``ontic ones'' (assuming the reality of states and wavefunctions). In particular, we show that relational type interpretations can readily accomodate the equivalence principle via a minor modification of the assumptions used to justify the formalism. We qualitatively speculate what a full generally covariant quantum dynamics could look like, and comment on experimental investigations.

quant-ph↗
arXiv2024

Meson spin alignment and baryon polarization from coalescence with spin-vorticity non-equilibrium

We estimate both the polarization of spin $1/2$ baryons and the spin density matrix coefficients of spin $1$ mesons using a thermal model that incorporates vorticity and polarization to describe quarks, along with a coalescence formalism where spin and vorticity are not in equilibrium. We find that while our model is not predictive due to its considerable number of free parameters, it has the potential to explain several seemingly puzzling features of experimental spin measurements, such as the absence of baryon polarization alongside significant vector meson spin alignment. We suggest the measuring meson spin off-diagonal matrix elements, and examining the dependence of polarization observables on azimuthal angles, as methods to falsify this model and gain insights into the freezeout details of baryon and meson spin structure.

hep-ph↗
arXiv2024

The Hanbury-Brown and Twiss effect in inflationary cosmological perturbations

The simplest model of inflation is based around an inflaton field that starts in a coherent false vacuum state with a positive cosmological constant, rolls slowly to the true vacuum and relaxes to it via reheating. We examine whether the scale of the transition from coherence to chaoticity can be examined via the Hanbury-Brown and Twiss (HBT) effect, in parallel with analogous problems of heavy ion physics (the ``pion laser'' and the thermalizing glasma). We develop an ansatz which contains a definition of ''chaoticity'' which parallels that of the usual setups where HBT is used. However, we also discuss the differences between the inflationary setup and more mainstream uses of HBT and conclude that these are more significant than the similarities, making the use of the developed methodology uncertain.

gr-qc↗
arXiv2024

Linearized fluctuating hydrodynamics via random polynomials

We argue that an ensemble of backgrounds best understands hydrodynamic dispersion relations in a medium with few degrees of freedom and is therefore subject to strong thermal fluctuations. In the linearized regime, dispersion relations become describeable by polynomials with random coefficients. We give a short review of this theory and perform a numerical study of the distribution of the roots of polynomials whose coefficients are of the order of a Knudsen series but fluctuate in accordance with canonical fluctuations of temperature. We find that, remarkably, the analytic structure of the poles of fluctuating dispersion relations is very different from deterministic ones, particularly regarding the distribution of imaginary parts with respect to real components. We argue that this provides evidence that hydrodynamic behavior persists, and is enhanced, by non-perturbative background fluctuations.

hep-th↗
arXiv2024

Vortex Rings in Event-by-Event Relativistic Heavy-Ion Collisions

We present event-by-event simulations for central asymmetric light+heavy and Au+Au collisions to investigate the formation and evolution of vortex-ring structures in the longitudinal flow velocity profile. The production-plane polarization of $Λ$ hyperons, defined w.r.t. the $Λ$ momentum and the beam, can track the "vortex-ring" feature in the event, a characteristic vortical structure generated by longitudinal flow gradients. We make comprehensive model predictions for the rapidity-dependent vortex-ring observables for different collision system sizes at $\sqrt{s_\mathrm{NN}} = 200$ and 72 GeV. Our predictions at the latter energy can be explored in the future LHCb fixed-target experiment at the Large Hadron Collider.

nucl-th↗
arXiv2024

Emergent symmetries of relativistic fluid dynamics from local ergodicity

We show that volume-preserving diffomorphisms and the chemical shift symmetry defining relativistic lagrangian ideal fluid dynamics can be derived as an emerging symmetry when ergodicity is assumed to apply locally in a way that is invariant under smooth spacetime foliations. This can be used as a way to derive the ideal hydrodynamic limit in a strongly coupled but strongly fluctuating medium. We comment on the connection with thermalization in small systems, the Eigenstate thermalization hypothesis and deviations from the ideal limit.

hep-th↗
arXiv2024

The functional generalization of the Boltzmann-Vlasov equation and its Gauge-like symmetry

We argue that one can model deviations from the ensemble average in non-equilibrium statistical mechanics by promoting the Boltzmann equation to an equation in terms of {\em functionals} , representing possible candidates for phase space distributions inferred from a finite observed number of degrees of freedom. We find that, provided the collision term and the Vlasov drift term are both included, a gauge-like redundancy arises which does not go away even if the functional is narrow. We argue that this effect is linked to the gauge-like symmetry found in relativistic hydrodynamics \cite{bdnk} and that it could be part of the explanation for the apparent fluid-like behavior in small systems in hadronic collisions and other strongly-coupled small systems\cite{zajc}. When causality is omitted this problem can be look at via random matrix theory show, and we show that in such a case thermalization happens much more quickly than the Boltzmann equation would infer. We also sketch an algorithm to study this problem numerically

cond-mat.stat-mech↗
arXiv2023

The equivalence principle and inertial-gravitational decoherence

This work is divided into two parts. The first examines recent proposals for "witnessing" quantum gravity via entanglement from the point of view of Bronstein's original objection to a quantization of gravity. Using techniques from open quantum systems we sketch how unavoidable decoherence from both inertial and gravitational backreaction between probe and detector could spoil the experimental detection of the quantization of gravity. We argue that this "failure" is actually an inherent feature of any quantum description that attempts to incorporate the equivalence principle exactly within quantum dynamics. In the second part, we speculate on how an exact realization of the equivalence principle might be implemented in an effective quantum field theory via the general covariance of correlators. While we are far from giving an explicit construction of such a theory we point out some features and consequences of such a program.

gr-qc↗
arXiv2023

Quarkonium spin alignment in a vortical medium

We use a potential model to investigate the phenomenology of quarkonium in a thermal rotating medium, where vorticity and spin density are not necessarily in equilibrium. We find that the quarkonium spin density matrix, as well as the binding energy and melting temperature, are sensitive to both the vorticity and the lack of equilibrium between vorticity and spin. This means that quarkonium spin alignment is a sensitive probe for vorticity and spin within the hydrodynamic phase. Information unequivocably pointing to spin-orbit non-equilibrium dynamics can be obtained from a combined study of quarkonium relative abundance and spin alignment, as well as experimentally obtainable off-diagonal density matrix elements.

hep-ph↗
arXiv2023

Neutrino oscillations in the interaction picture

We study the mixing of different kind of fields (scalar in 0+1D, scalar in 3+1D, fermion in 3+1D) treating the mixing term as an interaction. To this aim, we employ the usual perturbative series in the interaction picture. We find that expression for flavor changing probability exhibits corrections with respect to the usual quantum mechanical (e.g. neutrino) oscillation formula, in agreement with the result previously obtained in the non-perturbative flavor Fock space approach.

hep-ph↗
arXiv2023

$Λ$ polarization from vortex ring as medium response for jet thermalization

We performed a systematic study on the formation of vorticity rings as the process for jet thermalization in the medium created in high-energy nuclear collisions. In this work, we expanded our previous analysis to a more realistic framework by considering non-central events and fluctuations in the initial condition. We simulate the formation and evolution of the flow vortex structure in a relativistic viscous hydrodynamic model and study the sensitivity of the proposed ``ring observable'' ($\mathcal{R}^{t}_Λ$) that can be measured experimentally through the polarization of $Λ$ hyperons. We show that this observable is robust with respect to fluctuating initial conditions to capture the jet-induce vortex flow signal and further study its dependence on different model parameters, such as the jet's velocity, position, the fluid's shear viscosity, and the collision's centrality. The proposed observable is associated to the formation of vorticity in a quark-gluon plasma, showing that the measurement of particle polarization can be a powerful tool to probe different properties of jet-medium interactions and to understand better the polarization induced by the transverse and longitudinal expansions of the medium.

hep-ph↗
arXiv2022

An analysis of the spin density matrix of quarkonium in heavy ion collisions

In this addendum to [1], we apply the techniques developed in that paper to the $J/Ψ$ and $Υ$ spin alignement measurements in [2]. We argue that while the data points to a maximally impure density matrix, consistent with Cooper-Frye/Statistical model freeze-out, a measurement of the dependence of the $ϕ$-sensitive coefficients on the azimuthal angle with respect to the reaction plane would be the crucial test of this conclusion.

nucl-th↗
arXiv2022

Fluctuating relativistic dissipative hydrodynamics as a gauge theory

We argue that different formulations of hydrodynamics are related to uncertainties in the definitions of local thermodynamic and hydrodynamic variables. We show that this ambiguity can be resolved by viewing different formulations of hydrodynamics as particular "gauge choices" which lead to the same physical behavior of the system. Using the example of bulk viscosity, we show that Bemfica-Disconzi-Noronha-Kovtun (BDNK) and Israel-Stewart hydrodynamics are particular "gauge choices" of this type, related by a well-defined transformation of thermodynamic and hydrodynamic variables. We argue that this gauge ambiguity is necessary to ascertain the causality of stochastic hydrodynamic evolution and conjecture that it could explain the applicability of hydrodynamics outside its expected regime of validity since far from equilibrium and close to equilibrium may be related through transformations of this type.

hep-th↗
arXiv2022

Vector resonances spin alignement as a probe of spin hydrodynamics and freeze-out

We argue that a detailed analysis of the spin alignement of vector mesons can serve as a probe of two little-understood aspects of spin dynamics in the vortical fluid: The degree of relaxation between vorticity and parton spin polarization, and the degree of coherence of the hadron wavefunction at freeze-out. We illustrate these with a coalescence model.

nucl-th↗
arXiv2021

The strong CP problem, general covariance, and horizons

We discuss the strong CP problem in the context of quantum field theory in the presence of horizons. We argue that general covariance places constraints on the topological structure of the theory. In particular, as in QCD, it means that different topological sectors of the theory can only sum incoherently, because the degrees of freedom beyond the horizon must be traced over for general covariance to apply. This might lead to a solution of the so-called strong CP problem without extra observable dynamics.

hep-th↗
arXiv2021

Vortex rings from high energy central p+A collisions

Relativistic p+A collisions may produce droplets of quark gluon plasma (QGP) that quickly develop a toroidal vortex structure similar to that of an expanding smoke ring. We present viscous relativistic hydrodynamic calculations of ultra-central p+A collisions and develop an experimental observable to probe the structure, correlating the polarization and momentum of hyperons emitted from the collision. The effect is robust against changes in the definition of vorticity used to calculate the polarization. Experiments at RHIC and LHC may test the existence and strength of the vortex toroids, bringing new evidence to bear on the question of collectivity in the smallest QGP droplets.

hep-ph↗