arXiv subjects

Jacopo Ghiglieri

Publications and source records attributed to Jacopo Ghiglieri.

At least 19 recordsLinked to original sources

arXiv2026

Environmental sustainability in basic research: a perspective from HECAP+

The climate crisis and the degradation of the world's ecosystems require humanity to take immediate action. The international scientific community has a responsibility to limit the negative environmental impacts of basic research. The HECAP+ communities (High Energy Physics, Cosmology, Astroparticle Physics, and Hadron and Nuclear Physics) make use of common and similar experimental infrastructure, such as accelerators and observatories, and rely similarly on the processing of big data. Our communities therefore face similar challenges to improving the sustainability of our research. This document aims to reflect on the environmental impacts of our work practices and research infrastructure, to highlight best practice, to make recommendations for positive changes, and to identify the opportunities and challenges that such changes present for wider aspects of social responsibility.

physics.soc-ph↗

arXiv2026

AutoTherm: Automated Thermal Field Theory rates for cosmology

AutoTherm is a modular code automating the determination of thermal production and interaction rates for cosmology from Thermal Field Theory. This first release computes fully automatically the leading-order contribution from ultrarelativistic $2\leftrightarrow 2$ processes to the production rate of an off-equilibrium $\vartheta$ particle coupled to a thermal bath. It takes as input a FeynRules model file describing the Lagrangian of the bath-$\vartheta$ system. The AutoTherm program consists of a Wolfram package, which utilises FeynArts/FormCalc, together with a few Python modules for symbolic and numerical routines. Their combined usage leads from the model file to the rate, but each component can also be used in a standalone manner. The main strength of this release is the automated, model-independent handling of Hard Thermal Loop resummation, which is necessary whenever a $2\leftrightarrow 2$ process is mediated by a $t$-channel massless mediator. Developments in Thermal Field Theory reduce the apparently large model dependence to the determination of the thermal mass of the mediator, which we automate successfully. They further allow us to provide three leading-order-equivalent implementations of HTL resummation. Their spread provides a first estimate of the theory uncertainty from higher-order thermal corrections. We showcase the strength of our AutoTherm framework by successfully reproducing or correcting a host of results in the literature, such as the thermal production rate of ultrarelativistic right-handed neutrinos, of gravitons and gravitinos, of axions and of dark photons.

hep-ph↗

arXiv2026

Thermal gravitino and axino rate from AutoTherm

If ultrarelativistic supersymmetric particles are thermally produced in the early universe they would influence big-bang nucleosynthesis, dark matter and reheating constraints. While the basic framework for thermal gravitino and axino production is well established, the calculation is not completely settled. In this work, we revisit the problem using AutoTherm, a new tool which automates the computation of thermal rates from first-principles Thermal Field Theory, with control over the inherent theory uncertainty in Hard Thermal Loop resummation schemes. We demonstrate that the strict leading-order (LO) scheme, while unambiguous for hard momenta, can yield unphysical negative rates when extrapolated to soft momenta. To address this, we introduce a tuned scheme that ensures positivity and agreement with strict LO at high momenta, while avoiding gauge-dependent pathologies. We compare our results with existing parametrizations in the literature, identifying discrepancies and providing new, reliable fits for the gauge and Yukawa contributions to the gravitino and axino production rates. The choice of resummation scheme gives a theory uncertainty by a factor of $\sim 1.5$...$3$ depending on the temperature, which has been underappreciated until now. This residual spread should be taken into account in precision cosmological analyses of gravitino/axino abundancies.

hep-ph↗

arXiv2026

Energy and momentum dependence of the soft-axion interaction rate

Axions coupled to thermal non-Abelian gauge fields may have cosmological significance. As the heat bath defines a frame, its influence depends separately on energy and momentum. A light-like momentum ($k \approx ω$) is relevant for the axion contribution to the effective number of light neutrinos, $ΔN^{ }_\mathrm{eff}$, whereas a vanishing momentum ($k=0$) plays a role for warm natural inflation or ultralight dark matter, and has been employed in lattice estimates (both classical and quantum-statistical) of the strong sphaleron rate. Focussing on soft energies ($α_\mathrm{s}^{ }T \ll ω\ll πT$), we carry out an HTL computation to show how the domains $k=0$ and $k \approx ω$ interpolate to each other. We then compare with lattice data at $k=0$, and connect our analysis to NLO computations at $k \approx ω\ge πT$. Assembling the current best input, we re-investigate light QCD axion decoupling dynamics at $T \ge 200$ MeV, showing that efficient interactions in the ultrasoft domain increase $ΔN^{ }_\mathrm{eff}$ from $\sim 0.03$ to $\sim 0.04$ at $f^{ }_a = 4\times 10^8_{ }$ GeV.

hep-ph↗

arXiv2025

Thermal axion production at hard and soft momenta

Hot axions, thermally produced in the Early Universe, would contribute to dark radiation and are thus subject to present and future constraints from $N_{\rm eff}$. In this paper we quantify the contribution to $N_{\rm eff}$ and its uncertainty in models with axion-gluon couplings from thermal dynamics above the QCD transition. In more detail, we determine the leading-order thermal axion production rate for axion momenta of the order of the temperature adopting three different schemes for the incorporation of the collective dynamics of soft gluons. We show how these three schemes extrapolate differently into the regime of softer axion production, thus giving us a first quantitative handle on the theory uncertainty of the rate. Upon solving the Boltzmann equation, we find that this theory uncertainty translates to an uncertainty of order 0.002 for the contribution to $N_{\rm eff}$ prior to the QCD crossover. The uncertainty from common momentum-averaged approximations to the Boltzmann equation is smaller. We also discuss how QCD transition dynamics would need to be integrated into our results and we show how existing rate determinations in the literature based on gauge-dependent resummations are problematic.

hep-ph↗

arXiv2024

The force-force correlator at the hard thermal scale of hot QCD

High-energy particles traversing the Quark-Gluon plasma experience modified (massive) dispersion, although their vacuum mass is negligible compared to the kinetic energy. Due to poor convergence of the perturbative series in the regime of soft loop momenta, a more precise determination of this effective mass is needed. This paper continues our investigation on the factorisation between strongly-coupled infrared classical and perturbative ultraviolet behavior. The former has been studied non-perturbatively within EQCD by determining a non-local operator on the lattice. By computing the temperature-scale contribution to the same operator in 4D QCD at next-to-leading order (NLO), we remove the ultraviolet divergence of the EQCD calculation with an opposite infrared divergence from the hard thermal scale. The result is a consistent, regulator-independent determination of the classical contribution where the emergence of new divergences signals sensitivities to new regions of phase space. We address the numerical impact of the classical and NLO thermal corrections on the convergence of the factorised approach and on the partial applicability of our results to calculations of transport coefficients.

hep-ph↗

arXiv2024

Freezing-In Gravitational Waves

The thermal plasma in the early universe produced a stochastic gravitational wave (GW) background, which peaks today in the microwave regime and was dubbed the cosmic gravitational microwave background (CGMB). In previous works only single graviton production processes that contribute to the CGMB have been considered. Here we also investigate graviton pair production processes and show that these can lead to a significant contribution if the ratio between the maximum temperature and the Planck mass, $T_{\rm max}/m_{\rm p}$, divided by the internal coupling in the heat bath is large enough. As the dark matter freeze-in production mechanism is conceptually very similar to the GW production mechanism from the primordial thermal plasma, we refer to the latter as ``GW freeze-in production''. We show that quantum gravity effects appear in single graviton production and are smaller by a factor $(T_{\rm max}/m_{\rm p})^2$ than the leading order contribution. In our work we explicitly compute the CGMB spectrum within a scalar model with quartic interaction.

hep-ph↗

arXiv2023

Hard parton dispersion in the quark-gluon plasma, non-perturbatively

The in-medium dispersion of hard partons, encoded in their so-called asymptotic mass, receives large non-perturbative contributions from classical gluons, i.e. soft gluons with large occupation numbers. Here, we discuss how the analytical properties of thermal amplitudes allow for a non-perturbative determination of the infrared classical contribution through lattice determinations in the dimensionally-reduced effective theory of hot QCD, EQCD. We show how these lattice determinations need to be complemented by perturbative two-loop matching calculations between EQCD and QCD, so that the unphysical (classical) ultraviolet behavior of EQCD is replaced by its proper quantum QCD counterpart. We show how lattice and perturbative EQCD are in good agreement in the UV and present an outlook on the two-loop quantum QCD contribution.

hep-ph↗

arXiv2023

The force-force-correlator in hot QCD perturbatively and from the lattice

High-energy particles traversing a medium experience modified dispersion. In the Quark-Gluon Plasma, such dispersion affects jet propagation and transport properties and should be determined better. Above $\sim 2T_c$ we expect strongly coupled infrared behavior and perturbative ultraviolet behavior, allowing a perturbative matching to an effective theory called EQCD, which can be studied non-perturbatively. We study the relevant non-local operator in EQCD at next-to-leading order which allows for a complete EQCD-to-lattice match and prepares the groundwork for a matching between EQCD and full QCD. Our results in EQCD show remarkable agreement between perturbation theory and the lattice in the expected regime.

hep-ph↗

arXiv2023

The three-quark static potential in perturbation theory

We study the three-quark static potential in perturbation theory in QCD. A complete next-to-leading order calculation is performed in the singlet, octets and decuplet channels and the potential exponentiation is demonstrated. The mixing of the octet representations is calculated. At next-to-next-to-leading order, the subset of diagrams producing three-body forces is identified in Coulomb gauge and its contribution to the potential calculated. Combining it with the contribution of the two-body forces, which may be extracted from the quark-antiquark static potential, we obtain the complete next-to-next-to-leading order three-quark static potential in the colour-singlet channel.

hep-ph↗

arXiv2022

Classical vs quantum corrections to jet broadening in a weakly-coupled Quark-Gluon Plasma

The transverse momentum broadening coefficient $\hat{q}$ receives both soft, classical and radiative, quantum corrections. The former are responsible for a large O(g) correction, whereas the latter enter at relative order $α_s$, but are enhanced by a double logarithm of the length of the medium over the thermal wavelength. We analyze radiative corrections for a weakly-coupled quark-gluon plasma. We find that a thermal population of dynamical gluons changes the boundaries and reduces the size of the double-logarithmic phase space. It also provides new subdominant logarithmic corrections. We also show how the quantum, double-logarithmic and classical, soft phase spaces are smoothly connected once the radiated gluon becomes soft enough. Finally, we discuss a pathway to a determination of radiative corrections beyond the harmonic-oscillator approximation.

hep-ph↗

arXiv2022

Thermalization of weakly coupled non-Abelian plasmas at next-to-leading order

We employ the QCD kinetic theory, including next-to-leading(NLO) order corrections in coupling constant, to study the evolution of weakly coupled non-Abelian plasmas towards thermal equilibrium. For two characteristic far-from-equilibrium systems with either under- or over-occupied initial conditions, the NLO corrections remain well under control for a wide range of couplings, and the overall effect of NLO corrections is a reduction in the time required for thermalization.

hep-ph↗

arXiv2022

Transport properties of the QCD medium

I present an overview of recent developments in the microscopic description of the quark-gluon plasma. I will concentrate on medium-induced emission and transverse momentum broadening. These are two key ingredients of the theory of jet modifications in the QCD medium and of the kinetic theory used for transport and thermalisation. The main focus is on progress towards a better understanding of theory and of its uncertainties.

hep-ph↗

arXiv2022

Theories and Experiments for Testable Baryogenesis Mechanisms: A Snowmass White Paper

The baryon asymmetry of the Universe is one of the central motivations to expect physics beyond the Standard Model. In this Snowmass white paper, we review the challenges and opportunities in testing some of the central paradigms that predict physics at scales low enough to expect new experimental data in the next decade. Focusing on theoretical ideas and some of their experimental implications, in particular, we discuss neutron-antineutron transformations, flavor observables, next generation colliders, future neutron facilities, gravitational waves, searches for permanent electric dipole moments, $0νββ$ decay and some future large underground experiments as methods to test post-sphaleron baryogenesis, electroweak baryogenesis, mesogenesis and low scale leptogenesis. Finally, we comment on the cases where high scale physics can be probed through some of these same mechanisms.

hep-ph↗

arXiv2021

Thermalization of non-abelian gauge theories at next-to-leading order

We provide the first next-to-leading-order (NLO) weak-coupling description of the thermalization process of far-from-equilibrium systems in non-abelian gauge theory. We study isotropic systems starting from either over- or under-occupied initial conditions and follow their time evolution towards thermal equilibrium by numerically solving the QCD effective kinetic theory at NLO accuracy. We find that the NLO corrections remain well under control for a wide range of couplings and that the overall effect of NLO corrections is to reduce the time needed to reach thermal equilibrium in the systems considered.

hep-ph↗

arXiv2021

Freeze-in produced dark matter in the ultra-relativistic regime

When dark matter particles only feebly interact with plasma constituents in the early universe, they never reach thermal equilibrium. As opposed to the freeze-out mechanism, where the dark matter abundance is determined at $T \ll M$, the energy density of a feebly interacting state builds up and increases over $T \gtrsim M$. In this work, we address the impact of the high-temperature regime on the dark matter production rate, where the dark and Standard Model particles are ultra-relativistic and nearly light-like. In this setting, multiple soft scatterings, as well as $2 \to 2$ processes, are found to give a large contribution to the production rate. Within the model we consider in this work, namely a Majorana fermion dark matter of mass $M$ accompanied by a heavier scalar $-$ with mass splitting $ΔM$ $-$ which shares interactions with the visible sector, the energy density can be dramatically underestimated when neglecting the high-temperature dynamics. We find that the overall effective $1 \leftrightarrow 2$ and $2 \to2$ high-temperature contributions to dark-matter production give $\mathcal{O}(10)$ (20\%) corrections for $ΔM /M =0.1$ ($ΔM /M =10$) to the Born production rate with in-vacuum masses and matrix elements. We also assess the impact of bound-state effects on the late-time annihilations of the heavier scalar, in the context of the super-WIMP mechanism.

hep-ph↗

arXiv2020

Perturbative Thermal QCD: Formalism and Applications

In this review article, we discuss the current status and future prospects of perturbation theory as a means of studying the equilibrium thermodynamic and near-equilibrium transport properties of deconfined QCD matter. We begin with a brief introduction to the general topic, after which we review in some detail the foundations and modern techniques of the real- and imaginary-time formalisms of thermal field theory, covering e.g. the different bases used in the real-time formalism and the resummations required to deal with soft and collinear contributions. After this, we discuss the current status of applications of these techniques, including topics such as electromagnetic rates, transport coefficients, jet quenching, heavy quarks and quarkonia, and the Equations of State of hot quark-gluon plasma as well as cold and dense quark matter. Finally, we conclude with our view of the future directions of the field, i.e. how we anticipate perturbative calculations to contribute to our collective understanding of strongly interacting matter in the coming years.

hep-ph↗

arXiv2020

Thermal Heavy Quark Self-Energy from Euclidean Correlators

Brambilla, Escobedo, Soto, and Vairo have derived an effective description of quarkonium with two parameters; a momentum diffusion term and a real self-energy term. We point out that there is a similar real self-energy term for a single open heavy flavor and that it can be expressed directly in terms of Euclidean electric field correlators along a Polyakov line. This quantity can be directly studied on the lattice without the need for analytical continuation. We show that Minkowski-space calculations of this correlator correspond with the known NLO Euclidean value of the relevant electric field two-point function and that it differs from the real self-energy term for quarkonium.

hep-ph↗