242 research outputs found
Reconstructing Seesaws
We explore some aspects of "reconstructing" the heavy singlet sector of
supersymmetric type I seesaw models, for two, three or four singlets. We work
in the limit where one light neutrino is massless. In an ideal world, where
selected coefficients of the TeV-scale effective Lagrangian could be measured
with arbitrary accuracy, the two-singlet case can be reconstructed, two three
or more singlets can be differentiated, and an inverse seesaw with four
singlets can be reconstructed. In a more realistic world, we estimate \ell_\a
\to \ell_\b \gamma expectations with a "Minimal-Flavour-Violation-like"
ansatz, which gives a relation between ratios of the three branching ratios.
The two singlet model predicts a discrete set of ratios.Comment: 14 page
Complex CKM from Spontaneous CP Violation Without Flavor Changing Neutral Current
We analyse the general constraints on unified gauge models with spontaneous
CP breaking that satisfy the conditions that (i) CP violation in the quark
sector is described by a realistic complex CKM matrix, and (ii) there is no
significant flavor changing neutral current effects in the quark sector. We
show that the crucial requirement in order to conform to the above conditions
is that spontaneous CP breaking occurs at a very high scale by complex vevs of
standard model singlet Higgs fields. Two classes of models are found, one
consisting of pure Higgs extensions and the other one involving fermionic
extensions of the standard model. We give examples of each class and discuss
their possible embeddings into higher unified theories. One of the models has
the interesting property that spontaneous CP violation is triggered by
spontaneous P violation, thereby linking the scale of CP violation to the
seesaw scale for neutrino masses.Comment: Latex file ; 18 pages; No figures; some typos correcte
Quantum measurement in a family of hidden-variable theories
The measurement process for hidden-configuration formulations of quantum
mechanics is analysed. It is shown how a satisfactory description of quantum
measurement can be given in this framework. The unified treatment of
hidden-configuration theories, including Bohmian mechanics and Nelson's
stochastic mechanics, helps in understanding the true reasons why the problem
of quantum measurement can succesfully be solved within such theories.Comment: 16 pages, LaTeX; all special macros are included in the file; a
figure is there, but it is processed by LaTe
Constraints on the rare tau decays from mu --> e gamma in the supersymmetric see-saw model
It is now a firmly established fact that all family lepton numbers are
violated in Nature. In this paper we discuss the implications of this
observation for future searches for rare tau decays in the supersymmetric
see-saw model. Using the two loop renormalization group evolution of the soft
terms and the Yukawa couplings we show that there exists a lower bound on the
rate of the rare process mu --> e gamma of the form BR(mu --> e gamma) > C
BR(tau --> mu gamma) BR(tau --> e gamma), where C is a constant that depends on
supersymmetric parameters. Our only assumption is the absence of cancellations
among the high-energy see-saw parameters. We also discuss the implications of
this bound for future searches for rare tau decays. In particular, for large
regions of the mSUGRA parameter space, we show that present B-factories could
discover either tau --> mu gamma or tau --> e gamma, but not both.Comment: 39 pages, 7 figures. Typos corrected, references adde
An inverse approach to Einstein's equations for non-conducting fluids
We show that a flow (timelike congruence) in any type warped product
spacetime is uniquely and algorithmically determined by the condition of zero
flux. (Though restricted, these spaces include many cases of interest.) The
flow is written out explicitly for canonical representations of the spacetimes.
With the flow determined, we explore an inverse approach to Einstein's
equations where a phenomenological fluid interpretation of a spacetime follows
directly from the metric irrespective of the choice of coordinates. This
approach is pursued for fluids with anisotropic pressure and shear viscosity.
In certain degenerate cases this interpretation is shown to be generically not
unique. The framework developed allows the study of exact solutions in any
frame without transformations. We provide a number of examples, in various
coordinates, including spacetimes with and without unique interpretations. The
results and algorithmic procedure developed are implemented as a computer
algebra program called GRSource.Comment: 9 pages revtex4. Final form to appear in Phys Rev
The Interplay Between the "Low" and "High" Energy CP-Violation in Leptogenesis
We analyse within the "flavoured" leptogenesis scenario of baryon asymmetry
generation, the interplay of the "low energy" CP-violation, originating from
the PMNS neutrino mixing matrix , and the "high energy" CP-violation which
can be present in the matrix of neutrino Yukawa couplings, , and can
manifest itself only in "high" energy scale processes. The type I see-saw model
with three heavy right-handed Majorana neutrinos having hierarchical spectrum
is considered. The "orthogonal" parametrisation of the matrix of neutrino
Yukawa couplings, which involves a complex orthogonal matrix , is employed.
In this approach the matrix is the source of "high energy" CP-violation.
Results for normal hierarchical (NH) and inverted hierarchical (IH) light
neutrino mass spectrum are derived in the case of decoupling of the heaviest RH
Majorana neutrino. It is shown that taking into account the contribution to
due to the CP-violating phases in the neutrino mixing matrix can
change drastically the predictions for , obtained assuming only "high
energy" CP-violation from the -matrix is operative in leptogenesis. In the
case of IH spectrum, in particular, there exist significant regions in the
corresponding parameter space where the purely "high energy" contribution in
plays a subdominant role in the production of baryon asymmetry compatible
with the observations.Comment: Results unchanged; comments and references added; version to be
puplished in Eur.Phys.J.
On the mechanisms of heavy-quarkonium hadroproduction
We discuss the various mechanisms potentially at work in hadroproduction of
heavy quarkonia in the light of computations of higher-order QCD corrections
both in the Colour-Singlet (CS) and Colour-Octet (CO) channels and the
inclusion of the contribution arising from the s-channel cut in the CS channel.
We also discuss new observables meant to better discriminate between these
different mechanisms.Comment: Invited review talk at 3rd International Conference On Hard And
Electromagnetic Probes Of High-Energy Nuclear Collisions (HP2008), 8-14 June
2008, Illa da Toxa, Galicia, Spain. 11 pages, 21 figures, LaTeX, uses
svjour.cls and svepj.clo (included
Minimal Scenarios for Leptogenesis and CP Violation
The relation between leptogenesis and CP violation at low energies is
analyzed in detail in the framework of the minimal seesaw mechanism. Working,
without loss of generality, in a weak basis where both the charged lepton and
the right-handed Majorana mass matrices are diagonal and real, we consider a
convenient generic parametrization of the Dirac neutrino Yukawa coupling matrix
and identify the necessary condition which has to be satisfied in order to
establish a direct link between leptogenesis and CP violation at low energies.
In the context of the LMA solution of the solar neutrino problem, we present
minimal scenarios which allow for the full determination of the cosmological
baryon asymmetry and the strength of CP violation in neutrino oscillations.
Some specific realizations of these minimal scenarios are considered. The
question of the relative sign between the baryon asymmetry and CP violation at
low energies is also discussed.Comment: 36 pages, 5 figures; minor corrections and references updated. Final
version to appear in Phys. Rev.
From weak-scale observables to leptogenesis
Thermal leptogenesis is an attractive mechanism for generating the baryon
asymmetry of the Universe. However, in supersymmetric models, the parameter
space is severely restricted by the gravitino bound on the reheat temperature
. For hierarchical light neutrino masses, it is shown that thermal
leptogenesis {\it can} work when GeV. The low-energy
observable consequences of this scenario are . For higher , thermal leptogenesis works in a
larger area of parameter space, whose observable consequences are more
ambiguous. A parametrisation of the seesaw in terms of weak-scale inputs is
used, so the results are independent of the texture chosen for the GUT-scale
Yukawa matrices.Comment: a few references adde
Hierarchical Neutrino Mass Matrices, CP violation and Leptogenesis
In this work we study examples of hierarchical neutrino mass matrices
inspired by family symmetries, compatible with experiments on neutrino
oscillations, and for which there is a connection among the low energy CP
violation phase associated to neutrino oscillations, the phases appearing in
the amplitude of neutrinoless double beta decay, and the phases relevant for
leptogenesis. In particular, we determine the predictions from a texture based
on an underlying SU(3) family symmetry together with a GUT symmetry, and a
strong hierarchy for the masses of the heavy right handed Majorana masses. We
also give some examples of inverted hierarchies of neutrino masses, which may
be motivated in the context of U(1) family symmetries.Comment: 34 pages. Replaced with published version -typos, corrections and
references adde
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