Pauli Blocking Factors Research Articles

Concealing Dirac neutrinos from cosmic microwave background

The existence of prolonged radiation domination prior to the Big Bang Nucleosynthesis (BBN), starting just after the inflationary epoch, is not yet established unanimously. If instead, the universe undergoes a non-standard cosmological phase, it will alter the Hubble expansion rate significantly and may also generate substantial entropy through non-adiabatic evolution. This leads to a thumping impact on the properties of relic species decoupled from the thermal bath before the revival of the standard radiation domination in the vicinity of the BBN. In this work, considering the Dirac nature of neutrinos, we have studied decoupling of ultra-relativistic right-handed neutrinos (νR s) in presence of two possible non-standard cosmological phases. While in both cases we have modified Hubble parameters causing faster expansions in the early universe, one of the situations predicts a non-adiabatic evolution and thereby a slower redshift of the photon temperature due to the expansion. Considering the most general form of the collision term with Fermi-Dirac distribution and Pauli blocking factors, we have solved the Boltzmann equation numerically to obtain ΔNeff for the three right-handed neutrinos. We have found that for a large portion of parameter space, the combined effect of early decoupling of νR as well as the slower redshift of photon bath can easily hide the signature of right-handed neutrinos, in spite of precise measurement of ΔNeff, at the next generation CMB experiments like CMB-S4, SPT-3G etc. This however will not be applicable for the scenarios with only fast expansion.

Numerical solver for the time-dependent far-from-equilibrium Boltzmann equation

The study of strongly out-of-equilibrium states and their time evolution towards thermalization is critical to the understanding of an ever widening range of physical processes. We present a numerical method that for the first time allows for the numerical solution of the most difficult part of the time-dependent Boltzmann equation: the full scattering term. Any number of bands (and quasiparticles) with arbitrary dispersion, any number of high order scattering channels (we show here four legs scatterings: electron–electron scattering) can be treated far from equilibrium. No assumptions are done on the population and all the Pauli-blocking factors are included in the phase-space term of the scattering. The method can be straightforwardly interfaced to a deterministic solver for the transport. Finally and most critically, the method conserves to machine precision the particle number, momentum and energy for any resolution, making the computation of the time evolution till complete thermalization possible.We apply this approach to two examples, a metal and a semiconductor, undergoing thermalization from a strongly out-of-equilibrium laser excitation. These two cases, which are in literature treated hitherto under a number of approximations, can be addressed free from those approximations and straightforwardly within the same numerical method.

Generalized atomic processes for interaction of intense femtosecond XUV- and X-ray radiation with solids

Generalized atomic processes are proposed to establish a consistent description from the free-atom approach to the heated and even up to the cold solid. It is based on a rigorous introduction of the Fermi-Dirac statistics, Pauli blocking factors and on the respect of the principle of detailed balance via the introduction of direct and inverse processes. A probability formalism driven by the degeneracy of the free electrons enables to establish a link of atomic rates valid from the heated atom up to the cold solid. This allows to describe photoionization processes in atomic population kinetics and subsequent solid matter heating on a femtosecond time scale. The Auger effect is linked to the 3-body recombination via a generalized 3-body recombination that is identified as a key mechanism, along with the collisional ionization, that follows energy deposition by photoionization of inner shells when short, intense and high-energy radiation interacts with matter. Detailed simulations are carried out for aluminum that highlight the importance of the generalized approach.

EFFECTS OF NEUTRINO ELECTROMAGNETIC FORM FACTORS ON NEUTRINO INTERACTION WITH FINITE TEMPERATURE ELECTRON MATTERS

The differential cross-section of neutrino interaction with dense and warm electron gasses has been calculated by taking into account the neutrino electromagnetic form factors. The significant effect of electromagnetic properties of neutrino can be found if the neutrino dipole moment, μ ν , is ≥ 5.10-9 μB and neutrino charge radius, Rv, is ≥ 5.10-6 MeV-1. The importance of the retarded correction, detailed balance and Pauli blocking factors is shown and analyzed. Many-body effects on the target matter which are included via random phase approximation (RPA) correlation as well as photon effective mass are also investigated.

Photonuclear reactions at intermediate energies investigated via the Monte Carlo multicollisional intranuclear cascade model

The Monte Carlo multicollisional (MCMC) intranuclear cascade model is used to study photonuclear reactions at intermediate energies $(20\ensuremath{\leqslant}{E}_{\ensuremath{\gamma}}\ensuremath{\leqslant}140\phantom{\rule{0.3em}{0ex}}\mathrm{MeV})$. This version of the code differs from previous versions in the following aspects: (i) the quasideuteron model of photoabsorption is consistently included by taking into account relative momentum correlations of the neutron-proton pair in a relativistic kinematics; (ii) a realistic treatment of the Pauli-blocking mechanism at the initial photoabsorption and at each binary nucleon-nucleon scattering during the cascade process is incorporated throughout the calculations; (iii) a criterion based on energy considerations is required by the end of the cascade. Differently from other transport models used so far, which are based on a randomly generated nuclear ground state with a stochastic treatment of the Pauli blocking, the present model incorporates a shell constrained momentum space of the nucleons which is preserved as the cascade evolves along time. The transition between the pre-equilibrium and evaporation phases is energetically determined, allowing the description of the cascade process without any free parameter, such as some ambiguous stopping time parameters adopted in similar time-structured cascade models. The occupation number distribution after the cascade corresponds to a typical Fermi distribution at a finite nuclear temperature, and the long-standing spurious depletion of the Fermi sphere, usually present in other cascade models, no longer appears. The Pauli-blocking factors are calculated and compared with previous approaches based on Fermi gas level density calculations. The evaporation-fission process of the compound nucleus is described in the framework of a Monte Carlo algorithm. Experimental data of the total photoabsorption cross section and the neutron multiplicities for $\mathrm{Sn}$, $\mathrm{Ce}$, $\mathrm{Ta}$, and $\mathrm{Pb}$ in the $20--140\text{\ensuremath{-}}\mathrm{MeV}$ range are described fairly well by the present calculations.

Pauli blocking factors in quantum pumps

We investigate the Pauli blocking factor in quantum pumps using Floquet formalism. Even though the time dependent potentials in quantum pumping not only cause inelastic scatterings but also break the microreversibility, i.e., ${T}^{+}{(E}^{\ensuremath{'}},E)\ensuremath{\ne}{T}^{\ensuremath{-}}{(E,E}^{\ensuremath{'}}),$ the Pauli blocking factor is unnecessary when the scattering process through the scatterer is coherent. The well defined scattering states extending from one reservoir to the others form a complete nonorthogonal set. Regardless of the non-orthogonality one can obtain the pumped currents using the field operator formalism. The current expression finally obtained do not contain Pauli blocking factor.

Correlations in Hot and Dense Quark Matter

We present a relativistic three-body equation to investigate three-quark clusters in hot and dense quark matter. To derive such an equation we use the Dyson equation approach. The equation systematically includes the Pauli blocking factors as well as the self energy corrections of quarks. Special relativity is realized through the light front form. Presently we use a zero-range force and investigate the Mott transition.

Three- and Four-Body Correlations in Nuclear Matter

Few-nucleon correlations in nuclear matter at finite densities and temperatures are explored. Using the Dyson equation approach leads to effective few-body equations that include self energy corrections and Pauli blocking factors in a systematic way. Examples given are the nucleon deuteron in-medium reaction rates, few-body bound states including the $\ga$-particle, and $\ga$-particle condensation.

Probing Pauli Blocking Factors in Quantum Pumps with Broken Time-Reversal Symmetry

A recently demonstrated quantum electron pump is discussed within the framework of photon-assisted tunneling. Because of lack of time-reversal symmetry, different results are obtained for the pump current depending on whether or not final-state Pauli blocking factors are used when describing the tunneling process. While in both cases the current depends quadratically on the driving amplitude for moderate pumping, a marked difference is predicted for the temperature dependence. With blocking factors the pump current decreases roughly linearly with temperature until k(B)T approximately Planck's over 2piomega is reached, whereas without them it is unaffected by temperature, indicating that the entire Fermi sea participates in the transport.

Two‐particle energy spectrum in dense electron–hole plasmas

AbstractTwo‐particle (exciton) states in equilibrium electron–hole plasmas of highly excited semiconductors are determined. In the framework of the Green's function technique, an effective (two‐particle) wave equation allows to account for the influence of the surrounding plasma in terms of (dynamic) single‐particle self‐energies, Pauli blocking factors, and a dynamic effective potential correction. This equation is solved by expansion of the wave function in terms of Coulomb eigenfunctions. No rational or pole approximation for the dielectric function is used. Exciton binding energies and their imaginary parts (damping of the states) as well as continuum edges are given for Ge and GaAs model systems.

Resonant tunneling and charging effects in semiconductor quantum dots

The current in the stationary state through an interacting island coupled to several reservoirs is investigated. Recent discussions about the occurence of Pauli-blocking factors are clarified and a generalization of the linear-response theory of Coulomb-oscillations and cotunneling is presented for many-level quantum dots at low temperatures. A strong influence of repeated cotunneling processes on the resonant line shape is obtained.