arXiv subjects

Nicholas J. Benoit

Publications and source records attributed to Nicholas J. Benoit.

10 recordsLinked to original sources

arXiv2026

Non-perturbative quark production and transport in the evolving glasma: the WAGASHI event generator

We study non-perturbative quark-antiquark pair production and the subsequent quark dynamics in the earliest glasma stage of relativistic heavy-ion collisions. For that, we develop a new model, WAGASHI (Wong-precessing Anisotropic Glasma And ScHwinger-produced Initial-conditions), which combines classical Yang-Mills glasma evolution, Wong-equation transport, and Schwinger pair production on an event-by-event basis. We find that a sizeable number of quarks, comparable to the final hadron yields, are produced already during the glasma stage and subsequently undergo substantial momentum broadening and spin randomization, suggesting a significant contribution toward the early equilibration of the quark-gluon plasma. We also determine the event-by-event distributions of baryon number, electric charge, strangeness, and spin polarization in Pb-Pb and O-O collisions at LHC energies, finding particularly large fluctuations in the smaller O-O system. These results provide dynamical initial conditions for the subsequent hydrodynamic evolution of the quark-gluon plasma.

hep-ph↗

arXiv2026

Thermal dileptons to probe the baryon-rich QCD matter in the forward region of LHC energy heavy-ion collisions

We investigate thermal dilepton production from a quark-gluon plasma (QGP) with finite baryon chemical potential ($\mu_{\text{B}}$) in central Pb-Pb collisions at $\sqrt{s_{\text{NN}}}=5.02~\text{TeV}$. Recent studies suggest that sizable baryon densities can be achieved at forward rapidity even at LHC energies. We incorporate finite $\mu_{\text{B}}$ into a (3+1)-dimensional hydrodynamic framework and find that $\mu_{\text{B}}$ exceeds 500 MeV around $\eta_\text{s} = 6$ during the medium evolution. Using this framework, we calculate thermal dilepton spectra over a wide rapidity range and evaluate the impact of finite $\mu_{\text{B}}$ on dilepton production. A suppression of 3-4% is observed in the forward-rapidity region $5.2 < y < 7.2$ due to the reduced quark-antiquark abundance at finite baryon density. We further examine the effective temperature extracted from dilepton mass spectra in the intermediate-mass region $1.2 < M_{\ell \ell} < 2.6~\text{GeV}$ . The effective temperature remains strongly correlated with the underlying hydrodynamic temperature and retains sensitivity to the early high-temperature stage of the QGP evolution. These results demonstrate that forward-rapidity dileptons remain effective thermometers while providing sensitivity to finite baryon density at the LHC.

hep-ph↗

arXiv2025

Investigating effects of the electrical conductivity of QCD matter on charge-dependent directed flow

Charge dependent directed flow is an important observable of electromagnetic fields in relativistic heavy-ion collisions. We demonstrate how the difference in charge dependent directed flows between protons and antiprotons is sensitive to the resistivity, inverse of quark-gluon plasma's electric conductivity, over different collision centralities. Our model numerically solves the 3+1D relativistic resistive magneto-hydrodynamic (RRMHD) equations, assuming the electric conductivity to be a scalar. For this work, we focus on symmetric Au + Au collisions at the top RHIC energy of $\sqrt{s}=200$ GeV. We illustrate the time evolution of the electromagnetic fields in our model and connect that to the charge dependent directed flow results. Our results highlight the importance of modeling quark-gluon plasma's electric conductivity for charge dependent observables in relativistic heavy-ion collisions.

nucl-th↗

arXiv2024

Estimate of virtual photon polarization due to the intense magnetic field in Pb-Pb collisions at the LHC energies

We present the first numerical calculation of the virtual photon polarization and assess the feasibility of measuring the polarization via the anisotropic decay $\gamma^{*} \rightarrow \mu\mu$ using the LHC-ALICE detector. In presence of intense magnetic fields generated in high-energy non-central heavy-ion collisions that exceed the critical magnetic field intensity of quantum electrodynamics (QED), prompt virtual photons are predicted to decay anisotropically into lepton pairs, which we call virtual photon polarization. Using a relativistic resistive magnetohydrodynamics model, we computed the time evolution of the magnetic field and used these results to estimate the averaged polarization by calculating the vacuum polarization under the influence of the magnetic field at specific times. The estimated polarization deviates from zero with a statistical significance of $0.07\sigma$ with the data statistics collected from 2010 to 2011 and $0.15\sigma$ with the one from 2015 to 2018. It is understandable that the magnetic field could not be detected through polarization due to low statistical significance. With the data collecting the ongoing ALICE run from 2023 to 2026, the statistics dramatically increase by the upgraded LHC and the new data processing system. Thereby we expect that the statistical significance could reach $\sim 1.7\sigma$, resulting in a promising probe for detecting the intense magnetic fields.

hep-ph↗

arXiv2022

Determination of Majorana type-phases from the time evolution of lepton numbers

We have investigated an approach for determining the Majorana type-phases using the time evolution of lepton family numbers. We show how the second-order time derivative of the expectation values for the lepton family numbers depends on the sum of the Majorana type-phases. Furthermore, others have connected the Majorana type-phases to the orientation of unitary triangles for the PMNS matrix, and the usual Majorana phases. Theoretically,this allows for the extraction of the orientation of the triangles and the Majorana phases from lepton family numbers. We study three example situations. First, how to extract the Majorana type-phases and the lightest neutrino mass for three massive neutrinos, and when a neutrino is massless. Second,the determination of the Majorana phase and the lightest neutrino mass for a two generation toy model. Third, simplified realizations of the type I seesaw model with two gauge singlet neutrinos and two families of lepton doublets. We calculate how the Majorana phases and Majorana type-phases are related to CP violation for leptogenesis at high energies. At first,the effective Majorana mass matrix is parametrized with real and positive diagonal elements. In this basis, the phase of the off-diagonal elements are related to the CP violating phases in the PMNS matrix. We explicitly show the relation between the single Majorana phase and the phase of the effective Majorana mass matrix for the toy model with two generations of active neutrinos. Then for the model with two gauge singlet neutrinos and two families of lepton doublets, we study the effective Majorana mass matrix generated by the seesaw model. In that model, we can show how the Majorana phase at low energy is related to the two CP violating phases of the seesaw matrix. That relation between the phases depends on the lepton number asymmetries of the heavy Majorana neutrinos decays for the toy models.

hep-ph↗

arXiv2022

Renormalization group effects for a rank degenerate Yukawa matrix and the fate of the massless neutrino

The Type-I seesaw model is a common extension to the Standard Model that describes neutrino masses. The Type-I seesaw introduces heavy right-handed neutrinos with Majorana mass that transform as Standard Model electroweak gauge singlets. We initially study a case with two right-handed neutrinos called the 3-2 model. At an energy scale above the right-handed neutrinos, the effective neutrino mass matrix is rank degenerate implying the lightest neutrino is massless. After considering renormalization effects below the two right-handed neutrinos, the effective neutrino mass matrix remains rank degenerate. Next, we study a model with three right-handed neutrinos called the 3-3 model. Above the energy scale of the three right-handed neutrinos, we construct the effective neutrino mass matrix to be rank degenerate. After solving for the renormalization effects to energies below the three right-handed neutrinos, we find the rank of the effective neutrino mass matrix depends on the kernel solutions of the renormalization group equations. We prove for the simplest kernel solutions the effective neutrino mass matrix remains rank degenerate.

hep-ph↗

arXiv2022

Time evolution of the lepton number of Majorana neutrinos in the Schrödinger picture versus Heisenberg picture

In this paper, we study the time evolution of the expectation value of Majorana neutrino with the Schrödinger picture.The operators with the definite lepton number and operators with the definite mass are related to each other by a Bogolyubov transformation. Then the vacuum with the null lepton number is also related to the vacuum for the massive operator and it is written by the superposition of the vacuum for massive field and Majorana pairs condensed states. We choose the state with a definite lepton number $L$ $=1$ and the momentum ${\bf q}\ne 0$ as an initial state. By writing the state in terms of the superposition of energy eigenstates, we are able to study the time evolution of the state in the Schrödinger picture.The expectation value of lepton number operator is computed and it reproduces the same result as that obtained in the corresponding Heisenberg operator.

hep-ph↗

arXiv2021

Spacetime evolution of lepton number densities and wave packet-like effects for neutrino flavor and chiral oscillations in quantum field theory

We present a formulation of lepton family numbers, based on quantum field theory, for neutrino oscillation phenomenology that can be applied to nonrelativistic and relativistic energies for neutrinos. It is formulated for both types of neutrinos, Dirac and Majorana. The formulation is constructed as the time evolution of a lepton family number density operator. Then, the time evolution of the lepton family number density operator becomes dependent on the mass and new features appear. The expectation value of the density operator is evaluated for the initial state with a Gaussian distribution for the momentum amplitude. This enables us to study wave packet-like decoherence effects. We show in the nonrelativistic regime, the type of neutrino mass are distinguishable even under the presence of wave packet-like decoherence effects.

hep-ph↗

arXiv2021

Lepton family numbers and non-relativistic Majorana neutrinos

In this talk, we have reviewed the recent development on the time evolution of lepton family number carried by Majorana neutrinos \cite{Adam:2021qiq}. This article focuses on the subtle points of the derivation of the lepton family numbers and their time evolution. We also show how the time evolution is sensitive to $m_{ee}$ and $m_{eμ}$ components of the effective Majorana mass matrix by applying the formula to the two family case. The dependence on the Majorana phase is clarified and the implication on CNB (cosmic neutrino background) is also discussed.

hep-ph↗

arXiv2021

Time Evolution of Lepton Number Carried by Majorana Neutrinos

We revisit the time evolution of the lepton family number for a SU(2) doublet consisting of a neutrino and a charged lepton. The lepton family number is defined through the weak basis of the SU(2) doublet, where the charged lepton mass matrix is real and diagonal. The lepton family number carried by the neutrino is defined by the left-handed current of the neutrino family. For this work we assume the neutrinos have Majorana mass. This Majorana mass term is switched on at time $t=0$ and the lepton family number is evolved. Since the operator in the flavor eigenstate is continuously connected to that of the mass eigenstate, the creation and annihilation operators for the two eigenstates are related to each other. We compute the time evolution of all lepton family numbers by choosing a specific initial flavor eigenstate for a neutrino. The evolution is studied for relativistic and nonrelativistic neutrinos. The nonrelativistic region is of particular interest for the Cosmic Neutrino Background predicted from big bang models. In that region we find the lepton family numbers are sensitive to Majorana and Dirac phases, the absolute mass, and mass hierarchy of neutrinos.

hep-ph↗