arXiv subjects

Huaiyu Duan

Publications and source records attributed to Huaiyu Duan.

At least 37 records · Page 2Linked to original sources

arXiv2019

The dispersion relation of the fast neutrino oscillation wave

A dense neutrino medium can support flavor oscillation waves which are coherent among different momentum modes of the neutrinos. The dispersion relation (DR) branches of such a wave with complex frequencies and/or wave numbers can lead to the exponential growth of the wave amplitude which in turn will engender a collective flavor transformation in the neutrino medium. In this work we propose that the complex DR branches of the neutrino oscillation wave should be bound by the critical points of the DR. We demonstrate how this theory can be applied to the neutrino medium with an (approximate) axial symmetry about the propagation direction of the neutrino oscillation wave. We also show how the flavor instabilities in this medium can be identified by tracing the critical points of the DR as the electron lepton number distribution of the neutrino medium is changed continuously.

hep-ph↗

arXiv2018

Matter parametric neutrino flavor transformation through Rabi resonances

We consider the flavor transformation of neutrinos through oscillatory matter profiles. We show that the neutrino oscillation Hamiltonian in this case describes a Rabi system with an infinite number of Rabi modes. We further show that, in a given physics problem, the majority of the Rabi modes have too small amplitudes to be relevant. We also go beyond the rotating wave approximation and derive the relative detuning of the Rabi resonance when multiple Rabi modes with small amplitudes are present. We provide an explicit criterion of whether an off-resonance Rabi mode can affect the parametric flavor transformation of the neutrino.

hep-ph↗

arXiv2018

Fast neutrino flavor conversion: roles of dense matter and spectrum crossing

The flavor conversion of a neutrino usually occurs at densities $\lesssim G_F^{-1} ω$, whether in the ordinary matter or the neutrino medium, and on time/distance scales of order $ω^{-1}$, where $G_F$ is the Fermi weak coupling constant and $ω$ is the vacuum oscillation frequency of the neutrino. In 2005 Sawyer and more recently both he and other groups have shown that neutrino flavor conversions can occur on scales much shorter than $ω^{-1}$ in a very dense, anisotropic neutrino gas such as that in a core-collapse supernova or a binary neutron star merger. It has also been suggested that the fast neutrino flavor conversion require a crossing in the electron lepton number (ELN) angular distribution or spectrum. We study a few simple analytical models with which we elucidate the roles of the dense matter and the ELN spectrum crossing in neutrino fast flavor conversions. We show that a large matter density can induce fast neutrino flavor conversions in certain astrophysical scenarios such as at the early epoch of a core-collapse supernova.

hep-ph↗

arXiv2015

Neutrino flavor instabilities in a time-dependent supernova model

A dense neutrino medium such as that inside a core-collapse supernova can experience collective flavor conversion or oscillations because of the neutral-current weak interaction among the neutrinos. This phenomenon has been studied in a restricted, stationary supernova model which possesses the (spatial) spherical symmetry about the center of the supernova and the (directional) axial symmetry around the radial direction. Recently it has been shown that these spatial and directional symmetries can be broken spontaneously by collective neutrino oscillations. In this paper we analyze the neutrino flavor instabilities in a time-dependent supernova model. Our results show that collective neutrino oscillations start at approximately the same radius in both the stationary and time-dependent supernova models unless there exist very rapid variations in local physical conditions on timescales of a few microseconds or shorter. Our results also suggest that collective neutrino oscillations can vary rapidly with time in the regimes where they do occur which need to be studied in time-dependent supernova models.

astro-ph.HE↗

arXiv2015

Quantum Monte Carlo calculations of the thermal conductivity of neutron star crusts

We use the quantum Monte Carlo (QMC) techniques to calculate the static structure function $S(q)$ of a one-component ion lattice and use it to calculate the thermal conductivity $κ$ of high-density solid matter expected in the neutron star crust. By making detailed comparisons with the results for the thermal conductivity obtained using standard techniques based on the one-phonon approximation (OPA) valid at low temperature, and the multi-phonon harmonic approximation expected to be valid over a wide range of temperatures, we asses the temperature regime where $S(q)$ from QMC can be used directly to calculate $κ$. We also compare the QMC results to those obtained using classical Monte Carlo to quantitatively asses the magnitude of the quantum corrections. We find that quantum effects became relevant for the calculation of $κ$ at temperature $T \lesssim 0.3 ~Ω_\mathrm{P}$, where $Ω_\mathrm{P}$ is the ion plasma frequency. At $T \simeq 0.1 ~Ω_\mathrm{P}$ the quantum effects suppress $κ$ by about $30\%$. The comparison with the results of the OPA indicates that dynamical information beyond the static structure is needed when $T \lesssim 0.1~ Ω_\mathrm{P}$. These quantitative comparisons help to establish QMC as a viable technique to calculate $κ$ at moderate temperatures in the range $T=0.1-1~Ω_\mathrm{P}$ of relevance to the study of accreting neutron stars. This finding is especially important because QMC is the only viable technique so far for calculating $κ$ in multi-component systems at low-temperatures.

astro-ph.HE↗

arXiv2015

Performance Analysis of an Astrophysical Simulation Code on the Intel Xeon Phi Architecture

We have developed the astrophysical simulation code XFLAT to study neutrino oscillations in supernovae. XFLAT is designed to utilize multiple levels of parallelism through MPI, OpenMP, and SIMD instructions (vectorization). It can run on both CPU and Xeon Phi co-processors based on the Intel Many Integrated Core Architecture (MIC). We analyze the performance of XFLAT on configurations with CPU only, Xeon Phi only and both CPU and Xeon Phi. We also investigate the impact of I/O and the multi-node performance of XFLAT on the Xeon Phi-equipped Stampede supercomputer at the Texas Advanced Computing Center (TACC).

cs.DC↗

arXiv2015

Physics of neutrino flavor transformation through matter-neutrino resonances

In astrophysical environments such as core-collapse supernovae and neutron star-neutron star or neutron star-black hole mergers where dense neutrino media are present, matter-neutrino resonances (MNRs) can occur when the neutrino propagation potentials due to neutrino-electron and neutrino-neutrino forward scattering nearly cancel each other. We show that neutrino flavor transformation through MNRs can be explained by multiple adiabatic solutions similar to the Mikheyev-Smirnov-Wolfenstein mechanism. We find that for the normal neutrino mass hierarchy, neutrino flavor evolution through MNRs can be sensitive to the shape of neutrino spectra and the adiabaticity of the system, but such sensitivity is absent for the inverted hierarchy.

hep-ph↗

arXiv2015

Flavor instabilities in the multi-angle neutrino line model

Neutrino flavor oscillations in the presence of ambient neutrinos is nonlinear in nature which leads to interesting phenomenology that has not been well understood. It was recently shown that, in the two-dimensional, two-beam neutrino Line model, the inhomogeneous neutrino oscillation modes on small distance scales can become unstable at larger neutrino densities than the homogeneous mode does. We develop a numerical code to solve neutrino oscillations in the multi-angle/beam Line model with a continuous neutrino angular distribution. We show that the inhomogeneous oscillation modes can occur at even higher neutrino densities in the multi-angle model than in the two-beam model. We also find that the inhomogeneous modes on sufficiently small scales can be unstable at smaller neutrino densities with ambient matter than without, although a larger matter density does shift the instability region of the homogeneous mode to higher neutrino densities in the Line model as it does in the one-dimensional supernova Bulb model. Our results suggest that the inhomogeneous neutrino oscillation modes can be difficult to treat numerically because the problem of spurious oscillations becomes more severe for oscillations on smaller scales.

hep-ph↗

arXiv2015

Collective neutrino oscillations and spontaneous symmetry breaking

Neutrino oscillations in a hot and dense astrophysical environment such as a core-collapse supernova pose a challenging, seven-dimensional flavor transport problem. To make the problem even more difficult (and interesting), neutrinos can experience collective oscillations through nonlinear refraction in the dense neutrino medium in this environment. Significant progress has been made in the last decade towards the understanding of collective neutrino oscillations in various simplified neutrino gas models with imposed symmetries and reduced dimensions. However, a series of recent studies seem to have "reset" this progress by showing that these models may not be compatible with collective neutrino oscillations because the latter can break the symmetries spontaneously if they are not imposed. We review some of the key concepts of collective neutrino oscillations by using a few simple toy models. We also elucidate the breaking of spatial and directional symmetries in these models because of collective oscillations.

hep-ph↗

arXiv2015

Flavor instabilities in the neutrino line model

A dense neutrino medium can experience collective flavor oscillations through nonlinear neutrino-neutrino refraction. To make this multi-dimensional flavor transport problem more tractable, all existing studies have assumed certain symmetries (e.g., the spatial homogeneity and directional isotropy in the early universe) to reduce the dimensionality of the problem. In this work we show that, if both the directional and spatial symmetries are not enforced in the neutrino line model, collective oscillations can develop in the physical regimes where the symmetry-preserving oscillation modes are stable. Our results suggest that collective neutrino oscillations in real astrophysical environments (such as core-collapse supernovae and black-hole accretion discs) can be qualitatively different from the predictions based on existing models in which spatial and directional symmetries are artificially imposed.

hep-ph↗

arXiv2014

Multipole expansion method for supernova neutrino oscillations

We demonstrate a multipole expansion method to calculate collective neutrino oscillations in supernovae using the neutrino bulb model. We show that it is much more efficient to solve multi-angle neutrino oscillations in multipole basis than in angle basis. The multipole expansion method also provides interesting insights into multi-angle calculations that were accomplished previously in angle basis.

hep-ph↗

arXiv2013

Flavor Oscillation Modes In Dense Neutrino Media

We study two-flavor neutrino oscillations in homogeneous neutrino gases in which neutrinos and anti-neutrinos are in nearly pure weak interaction states initially. We find that the monopole and dipole oscillation modes can trigger flavor instabilities in the opposite neutrino mass hierarchies in a nearly isotropic neutrino gas. For a class of simple neutrino systems we are able to identify the normal modes of neutrino oscillations in the linear regime. Our results provide new insights into the recently discovered multi-azimuthal angle (MAA) instability of neutrino oscillations in supernovae.

hep-ph↗

arXiv2011

Neutrino Luminosity and Matter-Induced Modification of Collective Neutrino Flavor Oscillations in Supernovae

We show that the bump in the electron number density profile at the base of the hydrogen envelope in O-Ne-Mg core-collapse supernovae causes an interesting interplay between neutrino-electron and neutrino-neutrino forward scattering effects in the flavor evolution of low-energy nu_e in the neutronization burst. The bump allows a significant fraction of the low-energy nu_e to survive by rendering their flavor evolution nonadiabatic. Increasing the luminosity of the neutronization burst shifts the bump-affected nu_e to lower energy with reduced survival probability. Similarly, lowering the luminosity shifts the bump-affected neutrinos to higher energies. While these low energy neutrinos lie near the edge of detectability, the population of bump-affected neutrinos has direct influence on the spectral swap formation in the neutrino signal at higher energies.

astro-ph.HE↗

arXiv2011

Density Fluctuation Effects on Collective Neutrino Oscillations in O-Ne-Mg Core-Collapse Supernovae

We investigate the effect of matter density fluctuations on supernova collective neutrino flavor oscillations. In particular, we use full multi-angle, 3-flavor, self-consistent simulations of the evolution of the neutrino flavor field in the envelope of an O-Ne-Mg core collapse supernova at shock break-out (neutrino neutronization burst) to study the effect of the matter density "bump" left by the He-burning shell. We find a seemingly counterintuitive increase in the overall electron neutrino survival probability created by this matter density feature. We discuss this behavior in terms of the interplay between the matter density profile and neutrino collective effects. While our results give new insights into this interplay, they also suggest an immediate consequence for supernova neutrino burst detection: it will be difficult to use a burst signal to extract information on fossil burning shells or other fluctuations of this scale in the matter density profile. Consistent with previous studies, our results also show that the interplay of neutrino self-coupling and matter fluctuation could cause a significant increase in the electron neutrino survival probability at very low energy

astro-ph.HE↗

arXiv2011

Self-induced suppression of collective neutrino oscillations in a supernova

We investigate collective flavor oscillations of supernova neutrinos at late stages of the explosion. We first show that the frequently used single-angle (averaged coupling) approximation predicts oscillations close to, or perhaps even inside, the neutrinosphere, potentially invalidating the basic neutrino transport paradigm. Fortunately, we also find that the single-angle approximation breaks down in this regime; in the full multiangle calculation, the oscillations start safely outside the transport region. The new suppression effect is traced to the interplay between the dispersion in the neutrino-neutrino interactions and the vacuum oscillation term.

hep-ph↗

arXiv2010

The influence of collective neutrino oscillations on a supernova r-process

Recently, it has been demonstrated that neutrinos in a supernova oscillate collectively. This process occurs much deeper than the conventional matter-induced MSW effect and hence may have an impact on nucleosynthesis. In this paper we explore the effects of collective neutrino oscillations on the r-process, using representative late-time neutrino spectra and outflow models. We find that accurate modeling of the collective oscillations is essential for this analysis. As an illustration, the often-used "single-angle" approximation makes grossly inaccurate predictions for the yields in our setup. With the proper multiangle treatment, the effect of the oscillations is found to be less dramatic, but still significant. Since the oscillation patterns are sensitive to the details of the emitted fluxes and the sign of the neutrino mass hierarchy, so are the r-process yields. The magnitude of the effect also depends sensitively on the astrophysical conditions - in particular on the interplay between the time when nuclei begin to exist in significant numbers and the time when the collective oscillation begins. A more definitive understanding of the astrophysical conditions, and accurate modeling of the collective oscillations for those conditions, is necessary.

astro-ph.SR↗

arXiv2010

Multi-Angle Simulation of Flavor Evolution in the Neutrino Neutronization Burst From an O-Ne-Mg Core-Collapse Supernova

We report results of the first 3-by-3 "multi-angle" simulation of the evolution of neutrino flavor in the core collapse supernova environment. In particular, we follow neutrino flavor transformation in the neutronization neutrino burst of an O-Ne-Mg core collapse event. Though in a qualitative sense our results are consistent with those obtained in 3-by-3 single-angle simulations, at least in terms of neutrino mass hierarchy dependence, performing multi-angle calculations is found to reduce the adiabaticity of flavor evolution in the normal neutrino mass hierarchy, resulting in lower swap energies. Differences between single-angle and multi-angle results are largest for the normal neutrino mass hierarchy. Our simulations also show that current uncertainties in the measured mass-squared and mixing angle parameters translate into uncertainties in neutrino swap energies. Our results show that at low theta-13 it may be difficult to resolve the neutrino mass hierarchy using the O-Ne-Mg neutronization neutrino burst.

astro-ph.HE↗

arXiv2010

Collective Neutrino Oscillations

We review the rich phenomena associated with neutrino flavor transformation in the presence of neutrino self-coupling. Our exposition centers on three collective neutrino oscillation scenarios: a simple bipolar neutrino system that initially consists of mono-energetic electron neutrinos and antineutrinos; a homogeneous and isotropic neutrino gas with multiple neutrino/antineutrino species and continuous energy spectra; and a generic neutrino gas in an anisotropic environment. We use each of these scenarios to illustrate key facets of collective neutrino oscillations. We discuss the implications of collective neutrino flavor oscillations for core collapse supernova physics and for the prospects of obtaining fundamental neutrino properties, e.g., the neutrino mass hierarchy and $θ_{13}$ from a future observed supernova neutrino signal.

hep-ph↗