2,394 research outputs found
Leptogenesis in minimal predictive seesaw models
We estimate the Baryon Asymmetry of the Universe (BAU) arising from
leptogenesis within a class of minimal predictive seesaw models involving two
right-handed neutrinos and simple Yukawa structures with one texture zero. The
two right-handed neutrinos are dominantly responsible for the "atmospheric" and
"solar" neutrino masses with Yukawa couplings to proportional to and , respectively, where
is a positive integer. The neutrino Yukawa matrix is therefore characterised by
two proportionality constants with their relative phase providing a
leptogenesis-PMNS link, enabling the lightest right-handed neutrino mass to be
determined from neutrino data and the observed BAU. We discuss an SUSY
GUT example, where vacuum alignment provides the required Yukawa
structures with , while a symmetry fixes the relatives
phase to be a ninth root of unity.Comment: 16 pages, 2 tables. v2: minor changes, references added, version
accepted in JHE
On the nature of Lithium-rich giant stars: constraints from Beryllium abundances
We have derived beryllium abundances for 7 Li-rich giant (A(Li) > 1.5) stars
and 10 other Li-normal giants, with the aim of investigating the origin of the
Lithium in the Li-rich giants. In particular, we test the predictions of the
engulfment scenario proposed by Siess & Livio (1999), where the engulfment of a
brown dwarf or one or more giant planets would lead to a simultaneous
enrichment of 7Li and 9Be. We show that regardless their nature, none of the
stars studied in this paper were found to have detectable beryllium. Using
simple dilution arguments we show that the engulfment of an external object as
the sole source of Li enrichment is ruled out by the Li and Be abundance data.
The present results favor the idea that Li has been produced in the interior of
the stars by a Cameron-Fowler process and brought up to the surface by an extra
mixing mechanism.Comment: Accepted in A&
Unifying N=5 and N=6
We write the Lagrangian of the general N=5 three-dimensional superconformal
Chern-Simons theory, based on a basic Lie superalgebra, in terms of our
recently introduced N=5 three-algebras. These include N=6 and N=8
three-algebras as special cases. When we impose an antisymmetry condition on
the triple product, the supersymmetry automatically enhances, and the N=5
Lagrangian reduces to that of the well known N=6 theory, including the ABJM and
ABJ models.Comment: 19 pages. v2: Published version. Minor typos corrected, references
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