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Register a new userBeyond the MSW effect: Neutrinos in a dense medium
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We present a theory of neutrino oscillations in a dense medium which goes beyond the effective matter potential used in the description of the MSW effect. We show how the purity of the neutrino state is degraded by neutrino interactions with the environment and how neutrino--matter interactions can be a source of decoherence. We present new oscillation formulae for neutrinos interacting with leptons and carry out a numerical analysis which exhibits deviations from the MSW formulae for propagation through the Earth of ultra-high energy neutrinos. In particular, we show that at high density and/or high neutrino energy, the vanishing transition probabilities derived for MSW effect, are non zero when the scattering is taken into account.
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We consider Dirac neutrinos interacting with background fermions in the frame of the standard model. We demonstrate that a time-dependent effective potential is quite possible in a protoneutron star (PNS) at certain stages of its evolution. For the first time, we formulate a nonperturbative treatment of neutrino processes in a matter with arbitrary time-dependent effective potential. Using linearly growing effective potential, we study the typical case of a slowly varying matter interaction potential. We calculate differential mean numbers of $ u bar{ u}$ pairs created from the vacuum by this potential and find that they crucially depend on the magnitude of masses of the lightest neutrino eigenstate. These distributions uniformly span up to $sim 10$ eV energies for muon and tau neutrinos created in PNS core due to the compression just before the hydrodynamic bounce and up to $sim 0.1$ eV energies for all three active neutrino flavors created in the neutronization. Considering different stages of the PNS evolution, we derive constraints on neutrino masses, $m_{ u}lesssim (10^{-8}-10^{-7})$ eV corresponding to the nonvanishing $ u bar{ u}$ pairs flux produced by this mechanism. We show that one can distinguish such coherent flux from chaotic fluxes of any other origin. Part of these neutrinos, depending on the flavor and helicity, are bounded in the PNS, while antineutrinos of any flavor escape the PNS. If the created pairs are $ u_{e}bar{ u}_{e}$, then a part of the corresponding neutrinos also escape the PNS. The detection of $ u $ and $bar{ u}$ with such low energies is beyond current experimental techniques.
Assuming that at sufficiently high densities the constituent quarks become relevant degrees of freedom, we study within the framework of a chiral quark model the influence of s-wave $K^-$ condensation on the quark-antiquark condensates. We find that, in linear density approximation, the presence of a $K^-$ condensate quenches the $bar{u}u$ condensate, but that the $bar{d}d$ condensate remains unaffected up to the chiral order under consideration. We discuss the implication of the suppressed $bar{u}u$ condensate for flavor-dependent chiral symmetry restoration in dense matter
We investigate the stability of the pion string in a thermal bath and a dense medium. We find that stability is dependent on the order of the chiral transition. String core stability within the experimentally allowed regime is found only if the chiral transition is second order, and even there the stable region is small, i.e., the temperature below which the core is unstable is close to the critical temperature of the phase transition. We also find that the presence of a dense medium, in addition to the thermal bath, enhances the experimentally accessible region with stable strings. We also argue that once the string core decays, the effective winding of the string persists at large distances from the string core. Our analysis is done both in the chiral limit, which is mainly what has been explored in the literature up to now, and for the physical $h e 0$ case, where a conceptual framework is set up for addressing this regime and some simple estimates are done.
We report recent results on the dynamics of strange hadrons in two-body reactions relevant for near-threshold production in heavy-ion collisions at GSI/FAIR and NICA-Dubna. In particular, $bar K N$ scattering in hot and dense nuclear matter is studied within a chiral unitary framework in coupled channels, setting up the starting point for implementations in microscopic off-shell transport approaches. We focus on the calculation of transition rates with special attention to the excitation of hyperon resonances and isospin effects. Additionally, we explore unconventional strangeness generation by meson-meson and meson-baryon interactions in connection with recent HADES observations of deep sub-threshold $phi$ and $Xi$ production.
In this article, we have explored the very important quantity of lepton pair production from a hot and dense QCD medium in presence of an arbitrary magnetic field for simultaneous nonzero values of both the parallel and perpendicular components of momentum. As opposed to the zero magnetic field case (the so-called Born rate) or the lowest Landau level approximated rate, where only the annihilation process contributes, here we observe contributions also arising out of the quark and antiquark decay processes. We found the encouraging result of considerable enhancement of lepton pair production in presence of a magnetic field. We further decompose the total rate into different physical processes and make interesting observations for both zero and nonzero baryon density.
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