196,169 research outputs found
Synthesis of Majorana mass terms in low-energy quantum systems
No full textWe discuss the problem of how Majorana mass terms can be generated in low-energy systems. We show that, while these terms imply the Majorana condition, the opposite is not always true when more than one flavour is involved. This is an important aspect for the low-energy realizations of the Majorana mass terms exploiting superfluid pairings, because in this case the Majorana condition is not implemented in the spinor space, but in an internal (flavour) space. Moreover, these mass terms generally involve opposite effective chiralities, similarly to a Dirac mass term. The net effect of these features is that the Majorana condition does not imply a Majorana mass term. Accordingly the obtained Majorana spinors, as well as the resulting symmetry breaking pattern and low-energy spectrum, are qualitatively different from the ones known in particle physics. This result has important phenomenological consequences, e.g. implies that these mass terms are unsuitable to induce an effective see-saw mechanism, proposed to give mass to neutrinos. Finally, we introduce and discuss schemes based on space-dependent pairings with nonzero total momentum to illustrate how genuine Majorana mass terms may emerge in low-energy quantum systems
Hawking temperature and phonon emission in acoustic holes
No full textAcoustic holes are the hydrodynamic analog of standard black holes. Featuring an acoustic horizon, these systems spontaneously emit phonons at the Hawking temperature. We derive the Hawking temperature of the acoustic horizon by fully exploiting the analogy between black and acoustic holes within a covariant kinetic theory approach. After deriving the phonon distribution function from the covariant kinetic equations, we reproduce the expression of the Hawking temperature by equating the entropy and energy losses of the acoustic horizon and the entropy and energy gains of the spontaneously emitted phonons. Differently from previous calculations we do not need a microscopical treatment of normal mode propagation. Our approach opens a different perspective on the meaning of Hawking temperature and its connection with entropy, which may allow an easier study of nonstationary horizons beyond thermodynamic equilibrium, including dissipative effects
Non-Standard Neutrino Propagation and Pion Decay.
No full textMotivated by the findings of the OPERA experiment, we discuss the hypothesis that neutrino propagation does not obey Einstein special relativity. Under a minimal set of modifications of the standard model Lagrangian, we consider the implications of non standard neutrino propagation on the description of neutrino interactions and, specifically, on the pion decay processes. We show that all the different dispersion relations which have been proposed so far to explain OPERA results, imply huge departures from the standard expectations. The decay channel π+ → e+νe becomes significantly larger than in the standard scenario, and may even dominate over π+ → μ+νμ. Moreover, the spectral distribution of neutrinos produced in the decay processes and the probability that a pion decays in flight in neutrinos show large deviations from the standard results
Chromosomal evolution in Mugilidae (Pisces, Mugiliformes): FISH mapping of the (TTAGGG)n telomeric repeat in the six Mediterranean mullets.
No full textNeutron-mirror neutron mixing and neutron stars
No full textThe oscillation of neutron n into mirror neutron n′, its mass degenerate partner from dark mirror sector, can gradually transform the neutron stars into the mixed stars consisting in part of mirror dark matter. In quark stars n- n′ transitions are suppressed. We study the structure of mixed stars and derive the mass-radius scaling relations between the configurations of purely neutron star and maximally mixed star (MMS) containing equal amounts of ordinary and mirror components. In particular, we show that the MMS masses can be at most MNSmax/2, where MNSmax is a maximum mass of a pure neutron star allowed by a given equation of state. We evaluate n- n′ transition rate in neutron stars, and show that various astrophysical limits on pulsar properties exclude the transition times in a wide range 105year<1015year. For short transition times, τε< 10 5 year, the different mixed stars of the same mass can have different radii, depending on their age, which possibility can be tested by the NICER measurements. We also discuss subtleties related with the possible existence of mixed quark stars, and possible implications for the gravitational waves from the neutron star mergers and associated electromagnetic signals
Quasi-particle Specific Heats for the Crystalline Color Superconducting Phase of QCD
No full textWe calculate the specific heats of quasi-particles of two-flavor QCD in its crystalline phases for low temperature. We show that for the different crystalline structures considered here there are gapless modes contributing linearly in temperature to the specific heat. We evaluate also the phonon contributions which are cubic in temperature. These features might be relevant for compact stars with an inner shell in a color superconducting crystalline phase.We calculate the specific heats of quasi-particles of two-flavor QCD in its crystalline phases for low temperature. We show that for the different crystalline structures considered here there are gapless modes contributing linearly in temperature to the specific heat. We evaluate also the phonon contributions which are cubic in temperature. These features might be relevant for compact stars with an inner shell in a color superconducting crystalline phase
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