1,841 research outputs found
The electromagnetic ram action of the plasma focus as a paradigm for the generation of cosmic rays and the gigantic jets in active galaxies
Recent measurements of the energy spectrum of the plasma-focus-generated deuteron beam yield as spectrum of the form N(E)=(approx.) E to the -2.7 for 1MeV E 13 MeV. Other measurements show that the beta 1 electron beam which is generated simultaneously with the deuteron beam is interrupted into segments of spacing 25ps and duration approximately 4ps. A stuttering-electro-magnetic-ram (ser) model of the plasma focus in proposed which is similar to Raudorf's electronic ram which produces a similar spectrum for an electron beam for 1Mev E 10MeV. It is proposed that the cosmic ray spectrum and the giganic galactic jets are both generated by ser action near the centers of active galaxies
Baryonic masses based on the NJL model
We employ the Nambu Jona--Lasinio model to determine the vacuum pressure on
the quarks in a baryon and hence their density inside. Then we estimate the
baryonic masses by implementing the local density approximation for the mean
field quark energies obtained in a uniform and isotropic system. We obtain a
fair agreement with the experimental masses.Comment: 17 pages, 3 figures. to be published on EPJ
Shear Viscosity of Quark Matter
We consider the shear viscosity of a system of quarks and its ratio to the
entropy density above the critical temperature for deconfinement. Both
quantities are derived and computed for different modeling of the quark
self-energy, also allowing for a temperature dependence of the effective mass
and width. The behaviour of the viscosity and the entropy density is argued in
terms of the strength of the coupling and of the main characteristics of the
quark self-energy. A comparison with existing results is also discussed.Comment: 15 pages, 4 figure
The unbinding transition of mixed fluid membranes
A phenomenological model for the unbinding transition of multi-component
fluid membranes is proposed, where the unbinding transition is described using
a theory analogous to Flory-Huggins theory for polymers. The coupling between
the lateral phase separation of inclusion molecules and the membrane-substrate
distance explains the phase coexistence between two unbound phases as observed
in recent experiments by Marx et al. [Phys. Rev. Lett. 88, 138102 (2002)].
Bellow a critical end-point temperature, we find that the unbinding transition
becomes first-order for multi-component membranes.Comment: 7 pages, 3 eps figure
CP violation in scatterings, three body processes and the Boltzmann equations for leptogenesis
We obtain the Boltzmann equations for leptogenesis including decay and
scattering processes with two and three body initial or final states. We
present an explicit computation of the CP violating scattering asymmetries. We
analyze their possible impact in leptogenesis, and we discuss the validity of
their approximate expressions in terms of the decay asymmetry. In scenarios in
which the initial heavy neutrino density vanishes, the inclusion of CP
asymmetries in scatterings can enforce a cancellation between the lepton
asymmetry generated at early times and the asymmetry produced at later times.
We argue that a sizeable amount of washout is crucial for spoiling this
cancellation, and we show that in the regimes in which the washouts are
particularly weak, the inclusion of CP violation in scatterings yields a
reduction in the final value of the lepton asymmetry. In the strong washout
regimes the inclusion of CP violation in scatterings still leads to a
significant enhancement of the lepton asymmetry at high temperatures; however,
due to the independence from the early conditions that is characteristic of
these regimes, the final value of the lepton asymmetry remains approximately
unchanged.Comment: 24 pages, 6 figures. One appendix added. Some numerical results and
corresponding figures (mainly fig. 3) corrected. Final version to be
published in JHE
Mesonic correlation functions at finite temperature and density in the Nambu-Jona-Lasinio model with a Polyakov loop
We investigate the properties of scalar and pseudo-scalar mesons at finite
temperature and quark chemical potential in the framework of the
Nambu-Jona-Lasinio (NJL) model coupled to the Polyakov loop (PNJL model) with
the aim of taking into account features of both chiral symmetry breaking and
deconfinement. The mesonic correlators are obtained by solving the
Schwinger-Dyson equation in the RPA approximation with the Hartree (mean field)
quark propagator at finite temperature and density. In the phase of broken
chiral symmetry a narrower width for the sigma meson is obtained with respect
to the NJL case; on the other hand, the pion still behaves as a Goldstone
boson. When chiral symmetry is restored, the pion and sigma spectral functions
tend to merge. The Mott temperature for the pion is also computed.Comment: 24 pages, 9 figures, version to appear in Phys. Rev.
The importance of flavor in leptogenesis
We study leptogenesis from the out-of-equilibrium decays of the lightest
heavy neutrino in the medium (low) temperature regime, T\lsim 10^{12}
GeV ( GeV), where the rates of processes mediated by the (and
) Yukawa coupling are non negligible, implying that the effects of lepton
flavors must be taken into account. We find important quantitative and
qualitative differences with respect to the case where flavor effects are
ignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order of
magnitude; (ii) The sign of the asymmetry can be opposite to what one would
predict from the sign of the total lepton asymmetry ; (iii)
Successful leptogenesis is possible even with .Comment: 27 pages, 2 figures. Added 3 reference
Bounds on effective Majorana neutrino masses at HERA
The lepton-number violating process e p \to nu_e l l' X mediated by Majorana
neutrinos is studied for the HERA collider for (l l') = (e tau), (mu tau), (mu
mu) and (tau tau). Only the muonic decay of the tau is considered. The direct
limit on the effective muon Majorana mass, is improved
significantly to 4.0 times 10^3 GeV and for the first time direct limits on the
analogous effective masses connected with the tau sector are given, namely 4.2
times 10^3 GeV for , 4.4 times 10^3 GeV for and 2.0
times 10^4 GeV for . We find that a more general analysis for an
upgraded HERA could improve this values by a factor of up to 40, yet still
being orders of magnitude worse than indirect limits.Comment: 9 pages, 4 figures, revised versio
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