32 research outputs found
Lepton asymmetries and the growth of cosmological seed magnetic fields
Primordial cosmological hypermagnetic fields polarize the early
Universe plasma prior to the electroweak phase transition (EWPT).
As a result of the long range parity violating gauge interaction present in
the Standard Model their magnitude gets amplified, opening a new, perturbative
way, of accounting for the observed intergalactic magnetic fields.Comment: 4 pages, no figures, final published version available online at
http://www.iop.org/EJ/abstract/1029-8479/2008/03/06
Leptogenesis via hypermagnetic fields and baryon asymmetry
We study baryon asymmetry generation originated from the leptogenesis in the
presence of hypermagnetic fields in the early Universe plasma before the
electroweak phase transition (EWPT). For the simplest Chern-Simons (CS) wave
configuration of hypermagnetic field we find the baryon asymmetry growth when
the hypermagnetic field value changes due to alpha^2-dynamo and the lepton
asymmetry rises due to the Abelian anomaly. We solve the corresponding
integro-differential equations for the lepton asymmetries describing such
self-consistent dynamics for lepto- and baryogenesis in the two scenarios : (i)
when a primordial lepton asymmetry sits in right electrons e_R; and (ii) when,
in addition to e_R, a left lepton asymmetry for e_L and nu_eL arises due to
chirality flip reactions provided by inverse Higgs decays at the temperatures,
T<T_RL ~ 10 TeV. We find that the baryon asymmetry of the Universe (BAU) rises
very fast through such leptogenesis, especially, in strong hypermagnetic
fields. Varying (decreasing) the CS wave number parameter k_0 < 10^-7 T_EW one
can recover the observable value of BAU, eta_B ~ 10^-9, where k_0 = 10^-7 T_EW
corresponds to the maximum value for CS wave number surviving ohmic dissipation
of hypermagnetic field. In the scenario (ii) one predicts the essential
difference of the lepton numbers of right - and left electrons at EWPT time,
L_eR - L_eL ~ (mu_eR - mu_eL) / T_EW = Delta mu / T_EW ~ 10^-5 that can be used
as an initial condition for chiral asymmetry after EWPT.Comment: Erratum added, version to be published in JCA
Chern-Simons anomaly as polarization effect
The parity violating Chern-Simons term in the epoch before the electroweak
phase transition can be interpreted as a polarization effect associated to
massless right-handed electrons (positrons) in the presence of a large-scale
seed hypermagnetic field. We reconfirm the viability of a unified seed field
scenario relating the cosmological baryon asymmetry and the origin of the
protogalactic large-scale magnetic fields observed in astronomy.Comment: 4 pages, latex, matches published versio
Neutrino kinetics in a magnetized dense plasma
The relativistic kinetic equations (RKE) for lepton plasma in the presence of
a strong external magnetic field are derived in Vlasov approximation. The new
RKE for the electron spin distribution function includes the weak interaction
with neutrinos originated by the axial vector current () and provided
by the parity nonconservation. In a polarized electron gas Bloch equation
describing the evolution of the magnetization density perturbation is derived
from the electron spin RKE being modified in the presence of neutrino fluxes.
Such modified hydrodynamical equation allows to obtain the new dispersion
equation in a magnetized plasma from which the neutrino driven instability of
spin waves can be found. It is shown that this instability is more efficient
e.g. in a magnetized supernova than the analogous one for Langmuir waves
enhanced in an isotropic plasma.Comment: 20 pages, no figures, added subsection 2.3 about the lepton current
conservation, to be published in Astroparticle Physic
The electromagnetic vertex of neutrinos in an electron background and a magnetic field
We study the electromagnetic vertex function of a neutrino that propagates in
an electron background in the presence of a static magnetic field. The
structure of the vertex function under the stated conditions is determined and
it is written down in terms of a minimal and complete set of tensors. The
one-loop expressions for all the form factors is given, up to terms that are
linear in the magnetic field, and the approximate integral formulas that hold
in the long wavelength limit are obtained. We discuss the physical
interpretation of some of the form factors and their relation with the concept
of the neutrino induced charge. The neutrino acquires a longitudinal and a
transverse charge, due to the fact that the form factors depend on the
transverse and longitudinal components of the photon momentum independently. We
compute those form factors explicitly in various limiting cases and find that
the longitudinal and transverse charge are the same for the case of a
non-relativistic electron gas, but not otherwise.Comment: 18 pages. Revtex4, axodra
A potential test of the CP properties and Majorana nature of neutrinos
The scattering of solar neutrinos on electrons may reveal their CP
properties, which are particularly sensitive to their Majorana nature. The
cross section is sensitive to the neutrino dipole moments through an
interference of electro-magnetic and weak amplitudes. We show how future solar
neutrino experiments with good angular resolution and low energy threshold,
such as Hellaz, can be sensitive to the resulting azimuthal asymmetries in
event number, and could therefore provide valuable information on the CP
properties and the nature of the neutrinos, provided the solar magnetic field
direction is fixed.Comment: 14 pages, 1 figure, eq. (19) corrected. Version to be publishe
Low-energy solar anti-neutrinos
If neutrino conversions within the Sun result in partial polarization of
initial solar neutrino fluxes, then a new opportunity arises to observe the
anti-\nu_e's in future neutrino experiments in the low energy region (such as
BOREXINO or HELLAZ) and thus to probe the Majorana nature of the neutrinos. The
\nu_e -> anti-\nu_e conversions may take place for low energy solar neutrinos
while being unobservable at the Kamiokande and Super-Kamiokande experiments.Comment: Talk given at TAUP 97, Gran Sasso, Italy, Sep. 1997; LaTeX, 3 pages,
1 postscript figure, uses espcrc2.st
Neutrino Conversions in a Polarized Medium
Electron polarization induced by magnetic fields can modify the potentials
relevant for describing neutrino conversions in media with magnetic fields. The
magnitudes of polarization potentials are determined for different conditions.
We show that variations of the electron polarization along the neutrino
trajectory can induce resonant conversions in the active-sterile neutrino
system, but cannot lead to level crossing in the active-active neutrino system.
For neutrino flavour conversions the polarisation leads only to a shift of the
standard MSW resonance. For polarizations \lambda \lsim 0.04 the direct
modifications of the potential (density) due to the magnetic field pressure are
smaller than the modifications due to the polarization effect. We estimate that
indeed the typical magnitude of the polarization in the sun or in a supernova
are not expected to exceed . However even such a small polarization
may lead to interesting consequences for supernova physics and for properties
of neutrino signals from collapsing stars.Comment: Latex file, 24 pages including 8 ps figures, uses psfig.st
Dirac Neutrinos and Primordial Magnetic Fields
We consider random primordial magnetic fields and discuss their dissipation,
coherence length , scaling behaviour and constraints implied by the
primoridal nucleosynthesis. Such magnetic fields could excite the
right-helicity states of Dirac neutrinos, with adverse consequences for
nucleosynthesis. We present solutions to the spin kinetic equation of a Dirac
neutrino traversing a random magnetic field in the cases of large and small
, taking also into account elastic collisions. Depending on the scaling
behaviour and on the magnetic coherence length, the lower limit on the neutrino
magnetic moment thus obtained could be as severe as .Comment: 17 pages, HU-TFT-94-2
Gravitational Waves from a Pulsar Kick Caused by Neutrino Conversions
It has been suggested that the observed pulsar velocities are caused by an
asymmetric neutrino emission from a hot neutron star during the first seconds
after the supernova collapse. We calculate the magnitude of gravitational waves
produced by the asymmetries in the emission of neutrinos. The resulting
periodic gravitational waves may be detectable by LIGO and LISA in the event of
a nearby supernova explosion.Comment: 15 pages, 2 figure