1,978 research outputs found
Leptogenesis, Z' bosons, and the reheating temperature of the Universe
We study the impact for leptogenesis of new U(1) gauge bosons coupled to the
heavy Majorana neutrinos. They can significantly enhance the efficiency of
thermal scenarios in the weak washout regime as long as the Z' masses are not
much larger than the reheating temperature (), with the
highest efficiencies obtained for Z' bosons considerably heavier than the heavy
neutrinos (). We show how the allowed region of the parameter
space is modified in the presence of a Z' and we also obtain the minimum
reheating temperature that is required for these models to be successful.Comment: 14 pages, 6 figures; One figure added, discussion on the reheating
temperature extende
Simulation of the interaction of high-energy C60 cluster ions with amorphous targets
Detailed simulations of the interaction of energetic C-60 beams with amorphous targets are presented here. The spatial evolution of the cluster components is calculated accounting for multiple scattering and Coulomb explosion by means of Monte Carlo and molecular dynamics, respectively. The charge states of the individual cluster components (atoms, atomic ions, fragment cluster ions) as a function of penetration depth are also calculated in tandem with the above calculations by means of the Monte Carlo method. The relative importance of scattering versus Coulomb repulsion is studied as a function of the C-60 cluster energy. The effect of the neighboring cluster constituents on the average charge state of the cluster atoms is calculated as a function of the depth of penetration for a C-60 cluster of 40 MeV. The calculation accounts for the increase in ionization energy of the atom due to the other constituents. Relative track radii are calculated as a function of penetration depth and good agreement with the experimental results is obtained for the interaction of a 30 MeV carbon cluster with silicon. Track splitting observed well into the target as measured by Dunlop in yttrium iron garnet is obtained in the simulations described here for the case of amorphous carbon, provided the Coulomb repulsion is screened by the four valence electrons. Collective energy deposition enhancement is calculated for the 720 MeV cluster. Here the cluster constituents are nearly fully ionized, thereby minimizing the ambiguity related to the value of the ionic charge in the calculation
Simulation of the channelling of ions from MeV C60 in crystalline solids
Simulations were performed describing the motion and breakup of energetic C60 ions interacting with crystalline targets. A hybrid algorithm was used that employs a binary collision model for the scattering of the carbon ions by the atoms of the solid, and molecular dynamics for the Coulomb interactions of the 60 carbon ions with one another. For the case of yttrium iron garnet (YIG), directions such as [1 1 0], [1 0 0], [0 1 0] and [0 0 1] demonstrate channelling for a large fraction of the C ions. For directions such as [1 1 1], [2 1 1] and [7 5 3] the trajectories show no more channelling than for random directions. The effects of tilt, shielding and wake-field interactions were investigated for YIG and α-quartz
Dirac phase leptogenesis
I present here a concise summary of the preprint arXiv:0707.3024, written in
collaboration with A. Anisimov and P. Di Bari. There we discuss leptogenesis
when {\em CP} violation stems exlusively from the Dirac phase in the PMNS
mixing matrix. Under this assumption it turns out that the situation is very
constrained when a hierarchical heavy right-handed (RH) neutrino spectrum is
considered: the allowed regions are small and the final asymmetry depends on
the initial conditions. On the other hand, for a quasi-degenerate spectrum of
RH neutrinos, the {\em CP} asymmetry can be enhanced and the situation becomes
much more favorable, with no dependence on the initial conditions.
Interestingly, in the extreme case of resonant leptogenesis, in order to match
the observed baryon asymmetry of the Universe, we obtain a lower bound on \sin
\q_{13} which depends on the lightest active neutrino mass m_1.Comment: 3 pages, 2 figures, contribution to the proceedings of the TAUP 07
conference, Sep. 11-15, Sendai, Japa
Leptogenesis without violation of B-L
We study the possibility of generating the observed baryon asymmetry via
leptogenesis in the decay of heavy Standard Model singlet fermions which carry
lepton number, in a framework without Majorana masses above the electroweak
scale. Such scenario does not contain any source of total lepton number
violation besides the Standard Model sphalerons, and the baryon asymmetry is
generated by the interplay of lepton flavour effects and the sphaleron
decoupling in the decay epoch.Comment: V2 (published version): 21 pages, 4 figures. Some explanations have
been adde
Study of flavour dependencies in leptogenesis
We study the impact of flavours on the efficiency factors and give analytical
and numerical results of the baryon asymmetry taking into account the different
charged lepton Yukawa contributions and the complete (diagonal and
off-diagonal) to conversion matrix. With this treatment we update
the lower bound on the lightest right-handed neutrino mass.Comment: 13 pages, 11 figures. typos corrected, some formulae modified. 2
figures and discussion adde
On the full Boltzmann equations for Leptogenesis
We consider the full Boltzmann equations for standard and soft leptogenesis,
instead of the usual integrated Boltzmann equations which assume kinetic
equilibrium for all species. Decays and inverse decays may be inefficient for
thermalising the heavy-(s)neutrino distribution function, leading to
significant deviations from kinetic equilibrium. We analyse the impact of using
the full kinetic equations in the case of a previously generated lepton
asymmetry, and find that the washout of this initial asymmetry due to the
interactions of the right-handed neutrino is larger than when calculated via
the integrated equations. We also solve the full Boltzmann equations for soft
leptogenesis, where the lepton asymmetry induced by the soft SUSY-breaking
terms in sneutrino decays is a purely thermal effect, since at T=0 the
asymmetry in leptons cancels the one in sleptons. In this case, we obtain that
in the weak washout regime (K ~< 1) the final lepton asymmetry can change up to
a factor four with respect to previous estimates.Comment: 34 pages, 6 figures, to be published in JCA
Charge-Reversal Instability in Mixed Bilayer Vesicles
Bilayer vesicles form readily from mixtures of charged and neutral
surfactants. When such a mixed vesicle binds an oppositely-charged object, its
membrane partially demixes: the adhesion zone recruits more charged surfactants
from the rest of the membrane. Given an unlimited supply of adhering objects
one might expect the vesicle to remain attractive until it was completely
covered. Contrary to this expectation, we show that a vesicle can instead
exhibit {\it adhesion saturation,} partitioning spontaneously into an
attractive zone with definite area fraction, and a repulsive zone. The latter
zone rejects additional incoming objects because counterions on the interior of
the vesicle migrate there, effectively reversing the membrane's charge. The
effect is strongest at high surface charge densities, low ionic strength, and
with thin, impermeable membranes. Adhesion saturation in such a situation has
recently been observed experimentally [H. Aranda-Espinoza {\it et al.}, {\sl
Science} {\bf285} 394--397 (1999)]
The effect of age, sex and a firm-textured surface on postural control.
In previous studies, the influence of plantar sensation has been examined using various textured surfaces with different stiffness materials to assess static balance. This study investigated the effects of a Firm Textured Surface (FTS) along with age and sex-related influences on postural control under different visual conditions. Forty subjects (20 elderly, 10 males, mean age 68.30, 10 females, mean age 68.00, and 20 young people, 10 males, mean age 25.45, 10 females, mean age 27.30) participated in this study maintained a quiet standing on FTS, foam and firm surfaces with eyes open and closed. The center of pressure displacement (CoPDISP), CoP velocity (CoPVEL), and sway velocity of the CoP in anteroposterior (AP) and mediolateral (ML) direction (VA/P and VM/L) were measured. FTS was associated with lower postural sway measures in both the groups with eyes open and closed. However, the foam surface showed the worst results in all postural parameters under all experimental conditions. Separate four-way ANOVAs were applied to each dependent variable. The main effects of surface (p < 0.0001), vision (p < 0.0001) and age (p < 0.0001 for CoPDISP, CoPVEL and VA/P; p = 0.0003 for VM/L) were significant in each of the four fitted models. Sex was never significant, either as a main effect or an interaction with other experimental factors. Eyes open were able to reduce the negative effects of the foam surfaces but without vision the proprioceptive sensory system cues of the body state become more important for maintaining balance. A good stimulation with rigid texture should be considered as relief to reduce the physiological-related decline of afferent information with ag
Relationships and events: towards a general theory of reification and truthmaking.
We propose a novel ontological analysis of relations and relationships based on a re-visitation of a classic problem in the practice of knowledge repre- sentation and conceptual modeling, namely relationship reification. Our idea is that a relation holds in virtue of a relationship's existence. Relationships are therefore truthmakers of relations. In this paper we present a general theory or reification and truthmaking, and discuss the interplay between events and rela- tionships, suggesting that relationships are the focus of events, which emerge from the context (the scene) they occur in
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