We calculate the gravitational wave spectrum produced by magneto-hydrodynamic turbulence in a first order phase transitions. We focus in particular on the role of decorrelation of incompressible ...(solenoidal) homogeneous isotropic turbulence, which is dominated by the sweeping effect. The sweeping effect describes that turbulent decorrelation is primarily due to the small scale eddies being swept with by large scale eddies in a stochastic manner. This effect reduces the gravitational wave signal produced by incompressible MHD turbulence by around an order of magnitude compared to previous studies. Additionally, we find a more complicated dependence for the spectral shape of the gravitational wave spectrum on the energy density sourced by solenoidal modes (magnetic and kinetic). The high frequency tail follows either a k−5/3 or a k−8/3 power law for large and small solenoidal turbulence density parameter, respectively. Further, magnetic helicity tends to increase the gravitational wave energy at low frequencies. Moreover, we show how solenoidal modes might impact the gravitational wave spectrum from dilatational modes e.g. sound waves. We find that solenoidal modes greatly affect the shape of the gravitational wave spectrum due to the sweeping effect on the dilatational modes. For a high velocity flow, one expects a k−2 high frequency tail, due to sweeping. In contrast, for a low velocity flow and a sound wave dominated flow, we expect a k−3 high frequency tail. If neither of these limiting cases is realized, the gravitational wave spectrum may be a broken power law with index between −2 and −3, extending up to the frequency at which the source is damped by viscous dissipation.
Fast flavor conversions of supernova neutrinos, possible near the neutrinosphere, depends on an interesting interplay of collisions and neutrino oscillations. Contrary to naïve expectations, the rate ...of self-induced neutrino oscillations, due to neutrino-neutrino forward scattering, comfortably exceeds the rate of collisions even deep inside the supernova core. Consistently accounting for collisions and oscillations, we present the first calculations to show that collisions can create the conditions for fast flavor conversions of neutrinos, but oscillations can continue without significant damping thereafter. This may have interesting consequences for supernova explosions and the nature of its associated neutrino emission.
It has been speculated for a long time that neutrinos from a supernova (SN) may undergo fast flavor conversions near the collapsed stellar core. We perform a detailed study of this intriguing ...possibility, for the first time analyzing two time-dependent state-of-the-art three-dimensional (3D) SN models of 9 M⊙ and 20 M⊙ from recent papers of Glas et al. Both models were computed with multidimensional three-flavor neutrino transport based on a two-moment solver, and both exhibit the presence of the so-called lepton-number emission self-sustained asymmetry (LESA). The transport solution does not provide the angular distributions of the flavor-dependent neutrino fluxes, which are crucial to track the fast flavor instability. To overcome this limitation, we use a recently proposed approach based on the angular moments of the energy-integrated electron lepton-number distribution up to second order, i.e., angle-energy integrals of the difference between νe and ¯νe phase-space distributions multiplied by corresponding powers of the unit vector of the neutrino velocity. With this method we find the possibility of fast neutrino flavor instability at radii smaller than ∼ 20 km, which is well interior to the neutrinosphere where neutrinos are still in the diffusive and near-equilibrium regime. Our results confirm recent observations in a two-dimensional (2D) (axisymmetric) SN model and in 2D and 3D models with a fixed matter background, which were computed with Boltzmann neutrino transport. However, the flavor unstable locations are not isolated points as discussed previously, but thin skins surrounding volumes where ¯νe are more abundant than νe. These volumes grow with time and appear first in the convective layer of the proto-neutron star (PNS), where a decreasing electron fraction and high temperatures favor the occurrence of regions with negative neutrino chemical potential. Since the electron fraction remains higher in the LESA dipole direction, where convective lepton-number transport out from the nonconvective PNS core slows down the deleptonization, flavor unstable conditions become more widespread in the opposite hemisphere. This interesting phenomenon deserves further investigation, since its impact on SN modeling and possible consequences for SN dynamics and neutrino observations are presently unclear.
We investigate the evolution of the chiral magnetic instability in a protoneutron star and compute the resulting magnetic power and helicity spectra. The instability may act during the early cooling ...phase of the hot protoneutron star after supernova core collapse, where it can contribute to the buildup of magnetic fields of strength up to the order of 10{sup 14} G. The maximal field strengths generated by this instability, however, depend considerably on the temperature of the protoneutron star, on density fluctuations and turbulence spectrum of the medium. At the end of the hot cooling phase the magnetic field tends to be concentrated around the submillimeter to cm scale, where it is subject to slow resistive damping.
Despite the great progress made by modern cosmic ray observatories, the origin and acceleration mechanism of ultra-high-energy cosmic rays (UHECRs) remains unsolved problems to this day. However, ...there is experimental evidence for an anisotropic component in the UHECR arrival direction at energies greater than few EeV. The search for UHECR sources is further complicated by two main factors: during extragalactic propagation UHECRs interact with background photon fields (like the CMB and the EBL) and, since they are electrically charged, they are deflected by extragalactic and galactic magnetic fields (EGMF and GMF). Moreover, the strength, structure and origin of the EGMF are still not well known, causing reconstructing the deflection of UHECRs to be a non-trivial task. In this work we consider several EGMF models obtained from constrained MagnetoHydroDynamics (MHD) simulations of our local Universe to study the propagation of UHECRs through such a structured environment. We simulate propagation, interactions and observation of UHECRs by using the Monte Carlo code CRPropa3. We also take into account the effect of the GMF by adopting a lensing procedure of the arrival UHECR sky map. We explore several combination of source distribution, EGMF structure and mass composition. As a reference, we also simulate scenarios without the EGMF and with a statistically homogeneous field. We use our simulation results to compute UHECR observables, such as the energy spectrum, the angular power spectrum and the arrival direction map (before and after the GMF) in order to obtain constraints on possible combinations of source distributions and EGMF models.
Abstract
The landscape of high- and ultra-high-energy astrophysics has changed in the last decade, largely due to the inflow of data collected by large-scale cosmic-ray, gamma-ray, and neutrino ...observatories. At the dawn of the multimessenger era, the interpretation of these observations within a consistent framework is important to elucidate the open questions in this field. CRPropa 3.2 is a Monte Carlo code for simulating the propagation of high-energy particles in the Universe.
This version represents a major leap forward, significantly expanding the simulation framework and opening up the possibility for many more astrophysical applications. This includes, among others: efficient simulation of high-energy particles in diffusion-dominated domains, self-consistent and fast modelling of electromagnetic cascades with an extended set of channels for photon production, and studies of cosmic-ray diffusion tensors based on updated coherent and turbulent magnetic-field models. Furthermore, several technical updates and improvements are introduced with the new version, such as: enhanced interpolation, targeted emission of sources, and a new propagation algorithm (Boris push). The detailed description of all novel features is accompanied by a discussion and a selected number of example applications.
The presence of a primordial magnetic field would have induced resonant conversions between photons and axion-like particles (ALPs) during the thermal history of the Universe. These conversions would ...have distorted the blackbody spectrum of the cosmic microwave background (CMB). In this context, we derive bounds on the photon-ALP resonant conversions using the high precision CMB spectral data collected by the FIRAS instrument on board of the Cosmic Background Explorer. We obtain upper limits on the product of the photon-ALP coupling constant g times the magnetic field strength B down to gB 10-13 GeV-1 nG for ALP masses below the eV scale.
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