4,615 research outputs found
The Neutrino Mass Window for Baryogenesis
Interactions of heavy Majorana neutrinos in the thermal phase of the early
universe may be the origin of the cosmological matter-antimatter asymmetry.
This mechanism of baryogenesis implies stringent constraints on light and heavy
Majorana neutrino masses. We derive an improved upper bound on the CP asymmetry
in heavy neutrino decays which, together with the kinetic equations, yields an
upper bound on all light neutrino masses of 0.1 eV. Lepton number changing
processes at temperatures above the temperature T_B of baryogenesis can erase
other, pre-existing contributions to the baryon asymmetry. We find that these
washout processes become very efficient if the effective neutrino mass
\tilde{m}_1 is larger than m_* \simeq 10^{-3} eV. All memory of the initial
conditions is then erased. Hence, for neutrino masses in the range from (\Delta
m^2_sol)^{1/2} \simeq 8*10^{-3} eV to (\Delta m^2_atm)^{1/2} \simeq 5*10^{-2}
eV, which is suggested by neutrino oscillations, leptogenesis emerges as the
unique source of the cosmological matter-antimatter asymmetry.Comment: 29 pages, 12 figures include
Some Aspects of Thermal Leptogenesis
Properties of neutrinos may be the origin of the matter-antimatter asymmetry
of the universe. In the seesaw model for neutrino masses this leads to
important constraints on the properties of light and heavy neutrinos. In
particular, an upper bound on the light neutrino masses of 0.1 eV can be
derived. We review the present status of thermal leptogenesis with emphasis on
the theoretical uncertainties and discuss some implications for lepton and
quark mass hierarchies, CP violation and dark matter. We also comment on the
`leptogenesis conspiracy', the remarkable fact that neutrino masses may lie in
the range where leptogenesis works best.Comment: 23 pages, 5 figures, submitted to the Focus on Neutrino Physics issue
of the New Journal of Physics, edited by F. Halzen, M. Lindner and A. Suzuk
Cosmic Microwave Background, Matter-Antimatter Asymmetry and Neutrino Masses
We study the implications of thermal leptogenesis for neutrino parameters.
Assuming that decays of N_1, the lightest of the heavy Majorana neutrinos,
initiate baryogenesis, we show that the final baryon asymmetry is determined by
only four parameters: the CP asymmetry epsilon_1, the heavy neutrino mass M_1,
the effective light neutrino mass \tilde{m}_1, and the quadratic mean \bar{m}
of the light neutrino masses. Imposing the CMB measurement of the baryon
asymmetry as constraint on the neutrino parameters, we show, in a model
independent way, that quasi-degenerate neutrinos are incompatible with thermal
leptogenesis. For maximal CP asymmetry epsilon_1, and neutrino masses in the
range from (\Delta m^2_{sol})^{1/2} to (\Delta m^2_{atm})^{1/2}, the
baryogenesis temperature is T_B = O(10^{10}) GeV.Comment: 28 pages, 14 figures included; v2: erratum added, M_1 lower bound in
the strong wash-out regime (see Eq. (63)) relaxed by a factor 2/
Comparative Analysis Spread Spectrum and Parity Coding Steganography in E-commerce
The transaction data online has increased compared to the previous communications that mostly in the form of voice and text messaging. To improve the security, data must be protected such a way that it cannot be attacked by unauthorized parties. In this case, a good security system
must be able to transmit the original information to the second party without having to know the existence and validity by a third party. One of the security systems that
can be used is steganography. In this paper, we will compare the performance of Spread Spectrum and Parity Coding in e-commerce based on Android in case of processing time between insertion and retrieval information, and the changing image size during the insertion process. Our experimental results show that parity coding has better performance on client side that use low performance smart phone based on Android operating system and spread spectrum has better performance on blackberry store server that use laptop PC
Active-sterile neutrino oscillations in the early Universe: asymmetry generation at low |delta m^2| and the Landau-Zener approximation
It is well established that active-sterile neutrino oscillations generate
large neutrino asymmetries for very small mixing angles (), negative values of and provided that
. By numerically solving the quantum
kinetic equations, we show that the generation still occurs at much lower
values of . We also describe the borders of the generation at
small mixing angles and show how our numerical results can be analytically
understood within the framework of the Landau-Zener approximation thereby
extending previous work based on the adiabatic limit. This approximate approach
leads to a fair description of the MSW dominated regime of the neutrino
asymmetry evolution and is also able to correctly reproduce its final value. We
also briefly discuss the impact that neutrino asymmetry generation could have
on big bang nucleosynthesis, CMBR and relic neutrinos.Comment: 29 pages, 8 figures; to appear on Phys. ReV. D; figure 7 added, new
curves in figure 5a, new figure
Non-thermal leptogenesis with strongly hierarchical right handed neutrinos
Assuming the Dirac-type neutrino masses m_D are related to quark or charged
lepton masses, neutrino oscillation data indicate that right handed neutrino
masses are in general strongly hierarchical. In particular, if m_D is similar
to the up-type quark masses, the mass of the lightest right handed neutrino
M_1<~10^6 GeV. We show that non-thermal leptogenesis by inflaton decay can
yield sufficient baryon asymmetry despite this constraint, and discuss how the
asymmetry is correlated with the low energy neutrino masses and CP-violating
phases.Comment: 7 pages, 5 figures. v2: added some comments and references, v3: minor
corrections and additions, v4: a typo corrected, published versio
Leptogenesis implications in models with Abelian family symmetry and one extra real Higgs singlet
We show that the neutrino models, as suggested by Low, which have an
additional Abelian family symmetry and a real Higgs singlet to the default
see-saw do not hinder the possibility of successful thermal leptogenesis. For
these models (neglecting radiative effects), we have investigated the situation
of strong washout in both the one-flavor approximation and when flavor effects
are included. The result is that while such models predict that theta_{13}=0
and that one light neutrino to be massless, they do not modify or provide
significant constraints on the typical leptogenesis scenario where the final
asymmetry is dominated by the decays of the lightest right-handed neutrinos.Comment: 18 pages, RevTeX4, accepted by Phys. Rev. D. v2: minor corrections,
note and 1 ref. added, same content as published versio
Leptogenesis for Pedestrians
During the process of thermal leptogenesis temperature decreases by about one
order of magnitude while the baryon asymmetry is generated. We present an
analytical description of this process so that the dependence on the neutrino
mass parameters becomes transparent. In the case of maximal CP asymmetry all
decay and scattering rates in the plasma are determined by the mass M_1 of the
decaying heavy Majorana neutrino, the effective light neutrino mass tilde{m}_1
and the absolute mass scale bar{m} of the light neutrinos. In the mass range
suggested by neutrino oscillations, m_{sol} \simeq 8*10^{-3} eV \lesssim
\tilde{m}_1 \lesssim m_{atm} \simeq 5*10^{-2} eV, leptogenesis is dominated
just by decays and inverse decays. The effect of all other scattering processes
lies within the theoretical uncertainty of present calculations. The final
baryon asymmetry is dominantly produced at a temperature T_B which can be about
one order of magnitude below the heavy neutrino mass M_1. We also derive an
analytical expression for the upper bound on the light neutrino masses implied
by successful leptogenesis.Comment: 55 pages, 14 figures include
Exclusive and semi-inclusive strangeness and charm production in and reactions
Using the Quark-Gluon Strings Model (QGSM) combined with Regge phenomenology
we consider the reactions and which are dominated by the contributions of the and
Regge trajectories, respectively. The spin structure of the amplitudes is
described by introducing Reggeized Born terms. It is found that the existing
data for the reaction are in reasonable agreement
with the model predictions. To describe the absolute values of the cross
sections it is necessary to introduce also suppression factors which can be
related to absorption corrections. Furthermore, assuming the SU(4) symmetry to
hold for Regge residues and the universality of absorption corrections we
calculate the cross section of the reaction .
Employing the latter results from reactions we then estimate the
contributions of the pion exchange mechanism to the cross sections of the
reactions and and compare them
with the contributions of the and exchanges. We find that the
reactions are dominated not by pion exchange but by and exchanges,
respectively. Moreover, assuming the SU(4) symmetry to hold approximately for
the coupling constants = we analyze also
the production of leading hyperons in the reaction . It is shown that the non-perturbative mechanism should give an
essential contribution to the yield for .Comment: 3 pages, LaTeX, 4 postscript figures; contribution to QNP2002,
Juelich, June 10-14, 200
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