Nuclear Theory·nucl-th

Monday·February 12, 2024

15 papers—8 primary·7 cross-listed

09
Can quantum statistics help distinguish Dirac from Majorana neutrinos?
Evgeny Akhmedov🇩🇪 · Andreas Trautner🇩🇪
Finding out if neutrinos are Dirac or Majorana particles is known to be extremely difficult due to the smallness of neutrino mass and the fact that in the limit $m_{ν} = 0$ both Dirac and Majorana neutrinos become Weyl particles, i.e. are indistinguishable. There have been suggestions in the literature that in the case of processes with production of a neutrino-antineutrino pair (if neutrinos are Dirac particles) or two neutrinos (if they are of Majorana nature) quantum statistics may be of help. This is because for Majorana neutrinos quantum indistinguishability of identical particles requires the amplitude of the process to be antisymmetrized with respect to the interchange of the final-state neutrinos, whereas no such antisymmetrization must be done for Dirac neutrinos. It has been claimed that the resulting differences between the cross sections for Dirac and Majorana neutrinos persist even for arbitrarily small but not exactly vanishing neutrino mass. We demonstrate that, at least in the framework of the Standard Model, this is not the case. We also give a general proof that within the Standard Model quantum statistics does not help tell Dirac and Majorana neutrinos apart in the limit of negligibly small $m_{ν} / E$ .
↳ hep-phhep-exnucl-thJHEP(2024)·9 citations
10
Possible scenario of dynamical chiral symmetry breaking in the interacting instanton liquid model
Yamato Suda🇯🇵 · Daisuke Jido🇯🇵
We compute the vacuum energy density as a function of the quark condensate in the interacting instanton liquid model (IILM) and examine the pattern of dynamical chiral symmetry breaking from its behavior around the origin. This evaluation is performed by using simulation results of the IILM. We find that chiral symmetry is broken in the U(1)_A anomaly assisted way in the IILM with three-flavor dynamical quarks. We call such a symmetry breaking the anomaly-driven breaking which is one of the scenarios of chiral symmetry breaking proposed in the context of the chiral effective theories. We also find that the instanton-quark interaction included in the IILM plays a crucial role for the anomaly-driven breaking by comparing the full and the quenched IILM calculations.
↳ hep-phnucl-thPRD(2024)·4 citations
11
$ϕ^{n}$ trajectory bootstrap
Wenliang Li🇨🇳
We perform an extensive bootstrap study of Hermitian and non-Hermitian theories based on the novel analytic continuation of $⟨ ϕ^{n} ⟩$ or $⟨(i ϕ)^{n} ⟩$ in $n$ . We first use the quantum harmonic oscillator to illustrate various aspects of the $ϕ^{n}$ trajectory bootstrap method, such as the large $n$ expansion, matching conditions, exact quantization condition, and high energy asymptotic behavior. Then we derive highly accurate solutions for the anharmonic oscillators with the parity invariant potential $V (ϕ) = ϕ^{2} + ϕ^{m}$ and the $P T$ invariant potential $V (ϕ) = - (i ϕ)^{m}$ for a large range of integral $m$ , showing the high efficiency and general applicability of this new bootstrap approach. For the Hermitian quartic and non-Hermitian cubic oscillators, we further verify that the non-integer $n$ results for $⟨ ϕ^{n} ⟩$ or $⟨(i ϕ)^{n} ⟩$ are consistent with those from the wave function approach. In the $P T$ invariant case, the existence of $⟨(i ϕ)^{n} ⟩$ with non-integer $n$ allows us to bootstrap the non-Hermitian theories with non-integer powers, such as fractional and irrational $m$ .
↳ hep-thcond-mat.stat-mechhep-latnucl-th+1PRD(2025)·14 citations
12
Chiral spin symmetry and hot QCD
L. Ya. Glozman🇦🇹
In this talk we overview main results indicating existence in QCD of three qualitatively different regimes connected by smooth crossovers upon heating: a hadron gas, a stringy fluid and a quark-gluon plasma. In the combined large N_c and chiral limit these regimes likely become distinct phases separated by phase transitions: a chiral restoration phase transition around T_{ch} ~ 130 MeV and a deconfinement phase transition around T_d ~ 300 MeV. It should be an important task to verify this issue on the lattice. We will introduce a chiral spin symmetry, which is a symmetry of the electric part of electrodynamics and of QCD with light quarks. It is realized approximately in QCD above the chiral restoration crossover and disappears in the QGP regime. The center symmetry of the pure glue action and the chiral spin symmetry of the electric part of the QCD Lagrangian with light quarks are complementary to distinguish the confining regime and its disappearance. We also address other lattice evidences for stringy fluid: hadron resonances extracted from the lattice correlators; breakdown of the thermal perturbation theory at T < ~ 600 MeV and fluctuations of conserved charges that point out the N_c scaling above T ~ 155 MeV.
↳ hep-lathep-phhep-thnucl-thActa Phys.Polon.Supp.(2024)·3 citations
13
Contact interaction study of proton parton distributions
Yang Yu🇨🇳 · Peng Cheng🇨🇳 · Hui-Yu Xing🇨🇳 · Fei Gao🇨🇳 · Craig D. Roberts🇨🇳
Using a symmetry-preserving formulation of a vector $\times$ vector contact interaction (SCI) and treating the proton as a quark + interacting-diquark bound state, whose structure is obtained by solving a Poincaré-covariant Faddeev equation, we provide a comprehensive, coherent set of predictions for unpolarised and polarised proton parton distribution functions (DFs): valence, glue, and four-flavour separated sea. The results enable many themes to be addressed, including: the asymmetry of antimatter in the proton; the neutron:proton structure function ratio; helicity retention in hard scattering processes; the charm quark momentum fraction; the sign and size of the polarised gluon DF; and the origin of the proton spin. In all cases where sound analyses of data are available, SCI predictions are semiquantitatively in agreement with the results. Those mismatches which exist are typically attributable to the momentum-independence of the underlying interaction. Judiciously interpreted, the SCI delivers a sound and insightful explanation of proton structure as expressed in DFs.
↳ hep-phhep-exhep-latnucl-ex+1EPJC(2024)·24 citations
14
Damping of density oscillations from bulk viscosity in quark matter
Jose Luis Hernandez🇪🇸 · Cristina Manuel🇪🇸 · Laura Tolos🇪🇸
We study the damping of density oscillations in the quark matter phase that might occur in compact stars. To this end we compute the bulk viscosity and the associated damping time in three-flavor quark matter, considering both nonleptonic and semileptonic electroweak processes. We use two different equations of state of quark matter, more precisely, the MIT bag model and perturbative QCD, including the leading-order corrections in the strong coupling constant. We analyze the dependence of our results on the density, temperature and value of strange quark mass in each case. We then find that the maximum of the bulk viscosity is in the range of temperature from 0.01 to 0.1 MeV for frequencies around 1 kHz, while the associated minimal damping times of the density oscillations at those temperatures might be in the range of few to hundreds milliseconds. Our results suggest that bulk viscous damping might be relevant in the postmerger phase after the collision of two neutron stars if deconfined matter is achieved in the process.
↳ hep-phastro-ph.HEnucl-thPRD(2024)·19 citations
15
Real-time Dynamics of the Schwinger Model as an Open Quantum System with Neural Density Operators
Joshua Lin🇺🇸 · Di Luo🇺🇸 · Xiaojun Yao🇺🇸 · Phiala E. Shanahan🇺🇸
Ab-initio simulations of multiple heavy quarks propagating in a Quark-Gluon Plasma are computationally difficult to perform due to the large dimension of the space of density matrices. This work develops machine learning algorithms to overcome this difficulty by approximating exact quantum states with neural network parametrisations, specifically Neural Density Operators. As a proof of principle demonstration in a QCD-like theory, the approach is applied to solve the Lindblad master equation in the 1+1d lattice Schwinger Model as an open quantum system. Neural Density Operators enable the study of in-medium dynamics on large lattice volumes, where multiple-string interactions and their effects on string-breaking and recombination phenomena can be studied. Thermal properties of the system at equilibrium can also be probed with these methods by variationally constructing the steady state of the Lindblad master equation. Scaling of this approach with system size is studied, and numerical demonstrations on up to 32 spatial lattice sites and with up to 3 interacting strings are performed.
↳ hep-phhep-latnucl-thphysics.comp-ph+1JHEP(2024)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE

Can quantum statistics help distinguish Dirac from Majorana neutrinos?

Possible scenario of dynamical chiral symmetry breaking in the interacting instanton liquid model

ϕn trajectory bootstrap

Chiral spin symmetry and hot QCD

Contact interaction study of proton parton distributions

Damping of density oscillations from bulk viscosity in quark matter

Real-time Dynamics of the Schwinger Model as an Open Quantum System with Neural Density Operators

Affiliations

$ϕ^{n}$ trajectory bootstrap