arXiv subjects

Dmitry V. Naumov

Publications and source records attributed to Dmitry V. Naumov.

13 recordsLinked to original sources

arXiv2024

Infinite Series Solution of the Time-Dependent Radiative Transfer Equation in Anisotropically Scattering Media

We solve the radiative transfer equation (RTE) in anisotropically scattering media as an infinite series. Each series term represents a distinct number of scattering events, with analytical solutions derived for zero and single scattering. Higher-order corrections are addressed through numerical calculations or approximations. The RTE solution corresponds to Monte Carlo sampling of photon trajectories with fixed start and end points. Validated against traditional Monte Carlo simulations, featuring random end points, our solution demonstrates enhanced efficiency for both anisotropic and isotropic scattering functions, significantly reducing computational time and resources. The advantage of our method over Monte Carlo simulations varies with the position of interest and the asymmetry of light scattering, but it is typically orders of magnitude faster while achieving the same level of accuracy. The exploitation of hidden symmetries further accelerates our numerical calculations, enhancing the method's overall efficiency. In addition, we extend our analysis to the first and second moments of the photon's flux, elucidating the transition between transport and diffusive regimes.

hep-ph↗

arXiv2024

Exact Analytical Solution of the One-Dimensional Time-Dependent Radiative Transfer Equation with Linear Scattering

The radiative transfer equation (RTE) is a cornerstone for describing the propagation of electromagnetic radiation in a medium, with applications spanning atmospheric science, astrophysics, remote sensing, and biomedical optics. Despite its importance, an exact analytical solution to the RTE has remained elusive, necessitating the use of numerical approximations such as Monte Carlo, discrete ordinate, and spherical harmonics methods. In this paper, we present an exact solution to the one-dimensional time-dependent RTE. We delve into the moments of the photon distribution, providing a clear view of the transition to the diffusion regime. This analysis offers a deeper understanding of light propagation in the medium. Furthermore, we demonstrate that the one-dimensional RTE is equivalent to the Klein-Gordon equation with an imaginary mass term determined by the inverse reduced scattering length. Contrary to naive expectations of superluminal solutions, we find that our solution is strictly causal under appropriate boundary conditions, determined by the light transport problem. We validate the found solution using Monte Carlo simulations and benchmark the performance of the latter. Our analysis reveals that even for highly forward scattering, dozens of random light scatterings are required for an accurate estimate, underscoring the complexity of the problem. Moreover, we propose a method for faster convergence by adjusting the parameters of Monte Carlo sampling. We show that a Monte Carlo method sampling photon scatterings with input parameters $(μ_s,g)$, where $μ_s$ is the inverse scattering length and $g$ is the scattering anisotropy parameter, is equivalent to that with $(μ_s(1-g)/2,-1)$. This equivalence leads to a significantly faster convergence to the exact solution, offering a substantial improvement of the Monte Carlo method for the one-dimensional RTE.

physics.optics↗

arXiv2019

On coherent neutrino and antineutrino scattering off nuclei

Neutrino-nucleus $νA\to νA$ and antineutrino-nucleus $\barνA\to \barνA$ interactions, when the nucleus conserves its integrity, are discussed with coherent (elastic) and incoherent (inelastic) scattering regimes taken into account. In the first regime the nucleus remains in the same quantum state after the scattering and the cross-section depends on the quadratic number of nucleons. In the second regime the nucleus changes its quantum state and the cross-section has an essentially linear dependence on the number of nucleons. The coherent and incoherent cross-sections are driven by a nuclear nucleon form-factor squared $|F|^2$ term and a $(1-|F|^2)$ term, respectively. One has a smooth transition between the regimes of coherent and incoherent (anti)neutrino-nucleus scattering. Due to the neutral current nature these elastic and inelastic processes are indistinguishable if the nucleus recoil energy is only observed. One way to separate the coherent signal from the incoherent one is to register $γ$ quanta from deexcitation of the nucleus excited during the incoherent scattering. Another way is to use a very low-energy threshold detector and collect data at very low recoil energies, where the incoherent scattering is vanishingly small. In particular, for ${}^{133}\text{Cs}$ and neutrino energies of 30--50 MeV the incoherent cross-section is about 15-20\% of the coherent one. Therefore, the COHERENT experiment (with ${}^{133}\text{Cs}$) has measured the coherent elastic neutrino nucleus scattering (CE$ν$NS) with the inelastic admixture at a level of 15-20\%, if the excitation $γ$ quantum escapes its detection.

hep-ph↗

arXiv2019

Sterile Neutrino. A short introduction

This is a pedagogical introduction to the main concepts of the sterile neutrino - a hypothetical particle, coined to resolve some anomalies in neutrino data and retain consistency with observed widths of the $W$ and $Z$ bosons. We briefly review existing anomalies and the oscillation parameters that best describe these data. We discuss in more detail how sterile neutrino can be observed, as well as the consequences of its possible existence. In particular, we pay attention to a possible loss of coherence in a model of neutrino oscillations with sterile neutrinos, where this effect might be of a major importance with respect to the 3$ν$ model. The current status of searches for a sterile neutrino state is also briefly reviewed.

hep-ph↗

arXiv2018

Coherency and incoherency in neutrino-nucleus elastic and inelastic scattering

Neutrino-nucleus scattering $νA\to νA$, in which the nucleus conserves its integrity, is considered. We show that elastic interactions keeping the nucleus in the same quantum state lead to a quadratic enhancement of the corresponding cross-section in terms of the number of nucleons. Meanwhile, the cross-section of inelastic processes in which the quantum state of the nucleus is changed, essentially has a linear dependence on the number of nucleons. These two classes of processes are referred to as coherent and incoherent, respectively. The coherent and incoherent cross-sections are driven by factors $|F_{p/n}|^2$ and $(1-|F_{p/n}|^2)$, where $|F_{p/n}|^2$ is a proton/neutron form-factor of the nucleus, averaged over its initial states. The coherent cross-section formula used in the literature is revised and corrections depending on kinematics are estimated. As an illustration of the importance of the incoherent channel we considered three experimental setups with different nuclei. Experiments attempting to measure coherent neutrino scattering by solely detecting the recoiling nucleus, as is typical, might be including an incoherent background that is indistinguishable from the signal if the excitation gamma eludes its detection. However, as is shown here, the incoherent component can be measured directly by searching for photons released by the excited nuclei inherent to the incoherent channel. For a beam experiment these gammas should be correlated in time with the beam, and their higher energies make the corresponding signal easily detectable at a rate governed by the ratio of incoherent to coherent cross-sections. The detection of signals due to the nuclear recoil and excitation gammas provides a more sensitive instrument in studies of nuclear structure and possible signs of new physics.

hep-ph↗

arXiv2014

Recent results from Daya Bay experiment

This manuscript is a short summary of my talk given at ICNFP2014 Conference. Here we report on new results of $\sin^22θ_{13}$ and $Δm^2_\text{ee}$ measurements, search for the sterile neutrino within $10^{-3} \text{ eV}^2 <Δm^2_{41}<0.1\text{ eV}^2$ domain and precise measurement of the reactor absolute antineutrino flux.

hep-ex↗

arXiv2011

Recent results in neutrino physics

This manuscript is a shorthand version of my talk given at Odessa Gamov School on Astronomy, Cosmology and Beyond (22-28 August 2011, Odessa, Ukraine). Within this note we very briefly review the main achievements, new results and open problems in neutrino physics of today.

physics.pop-ph↗

arXiv2011

Neutrino Velocity Anomalies: A Resolution without a Revolution

We argue that the neutrino advance of time observed in MINOS and OPERA experiments can be explained in the framework of the standard relativistic quantum theory as a manifestation of the large effective transverse size of the eigenmass neutrino wavepackets.

hep-ph↗

arXiv2010

A diagrammatic treatment of neutrino oscillations

We present a covariant wave-packet approach to neutrino flavor transitions in vacuum. The approach is based on the technique of macroscopic Feynman diagrams describing the lepton number violating processes of production and absorption of virtual massive neutrinos at the macroscopically separated space-time regions ("source" and "detector"). Accordingly, the flavor transitions are a result of interference of the diagrams with neutrinos of different masses in the intermediate states. The statistically averaged probability of the process is representable as a multidimensional integral of the product of the factors which describe the differential flux density of massless neutrinos from the source, differential cross section of the neutrino interaction with the detector and a dimensionless factor responsible for the flavor transition. The conditions are analyzed under which the last factor can be treated as the flavor transition probability in the usual quantum-mechanical sense.

hep-ph↗

arXiv2002

Lambda Polarization in Deep-Inelastic Production

We propose a model for the longitudinal polarization of Lambda baryons produced in deep-inelastic lepton scattering at any xF, based on static SU(6) quark-diquark wave functions and polarized intrinsic strangeness in the nucleon associated with individual valence quarks. Free parameters of the model are fixed by fitting the NOMAD data on the longitudinal polarization of Lambda hyperons in neutrino interactions. Our model correctly reproduces the observed dependences of Lambda polarization on the kinematic variables. Within the context of our model, the NOMAD data imply that the intrinsic strangeness associated with a valence quark has anticorrelated polarization. We also compare our model predictions with results from the HERMES and E665 experiments using charged leptons. Predictions of our model for the COMPASS experiment are also presented.

hep-ph↗

arXiv2002

Measurement of Lambda and Lambda-bar polarization in muon neutrino charged current interactions in NOMAD

The Lambda and Lambda-bar polarizations in muon neutrino charged current interactions have been measured in the NOMAD experiment. The event sample (8087 reconstructed Lambda's and 649 Lambda-bar's) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. For the Lambda hyperons we observe negative polarization along the W-boson direction which is enhanced in the target fragmentation region: Px(xF < 0) = -0.21 +- 0.04 (stat) +- 0.02 (sys). In the current fragmentation region we find Px(xF > 0) = -0.09 +- 0.06 (stat) +- 0.03(sys). A significant transverse polarization (in the direction orthogonal to the Lambda production plane) has been observed for the first time in a neutrino experiment: Py = -0.22 +- 0.03 (stat) +- 0.01 (sys). The dependence of the absolute value of Py on the Lambda transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron-hadron experiments. The polarization vector of Lambda-bar hyperons measured for the first time in neutrino interactions is found to be consistent with zero.

hep-ph↗

arXiv2002

Intrinsic Polarized Strangeness and Lambda Polarization in Deep-Inelastic Production

We propose a model for the longitudinal polarization of Lambda baryons produced in deep-inelastic lepton scattering at any xF, based on static SU(6) quark-diquark wave functions and polarized intrinsic strangeness in the nucleon associated with individual valence quarks. Free parameters of the model are fixed by fitting NOMAD data on the longitudinal polarization of Lambda hyperons in neutrino collisions. Our model correctly reproduces the observed dependences of Lambda polarization on the kinematic variables. Within the context of our model, the NOMAD data imply that the intrinsic strangeness associated with a valence quark has anticorrelated polarization. We also compare our model predictions with results from the HERMES and E665 experiments using charged leptons. Predictions of our model for the COMPASS experiment are also presented.

hep-ph↗

arXiv2001

Measurement of Lambda polarization in muon neutrino charged current interactions in NOMAD

The Lambda polarization in muon neutrino charged current interactions has been measured in the NOMAD experiment. We observe negative polarization along the W - boson direction which is enhanced in the target fragmentation region: Px (xF < 0) = -0.21 +/- 0.04(stat) +/- 0.02(sys). In the current fragmentation region we find: Px (xF > 0) = -0.09 +/- 0.06(stat) +/- 0.03(sys). These results provide a test of different models describing the nucleon spin composition and the spin transfer mechanisms. A significant transverse polarization (in the direction orthogonal to the Lambda production plane) has been observed for the first time in a neutrino experiment: Py = -0.22 +/- 0.03(stat) +/- 0.01(sys). The dependence of the absolute value of Py on the Lambda transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron-hadron experiments.

hep-ph↗