153 research outputs found
Neutrino and astroparticle physics : Working group report
The contributions made to the Working Group activities on neutrino and
astroparticle physics are summarised in this article. The topics discussed were
leptogenesis in Left-Right symmetric model, inflationary models in
Raman-Sundrum scenarios, ultra high energy cosmic rays and neutrino
oscillations in 4 flavour and decaying neutrino models.Comment: 11 pages; arXiv copy of contribution to WHEPP-6 proceeding
Cosmology in a supersymmetric model with gauged
We consider salient cosmological features of a supersymmetric model which is
Left-Right symmetric and therefore possessing gauged symmetry. The
requirement of breaking parity and also obtaining charge preserving vacua
introduces some unique features to this model (MSLRM), resulting in a
preference for non-thermal Leptogenesis. Assuming that the model preserves TeV
scale supersymmetry, we show that the vacuum structure generically possesses
domain walls, which can serve two important purposes. They can signal a
secondary inflation required to remove unwanted relics such as gravitino and
moduli and also generate lepton asymmetry by a mechanism similar to electroweak
baryogenesis. The requirement of disappearance of domain walls imposes
constraints on the soft parameters of the theory, testable at the TeV scale. We
also propose an alternative model with spontaneous parity violation
(MSLR\rlap/P). Incorporating the same cosmological considerations in this case
entails constraints on a different set of soft parameters.Comment: 18 pages. Minor changes in text, but conclusion remains same.
Published in Phys. Rev.
Bubble wall dynamics, generalised Yukawa couplings and adequate electroweak baryogenesis in two-Higgs-doublet model
Baryogenesis at the electroweak scale depends on divers but identifiable
details of bubble wall dynamics and the particle physics. We show that
inclusion of the dynamics of relative phase in two-Higgs-doublet model (2HDM)
enhances the adiabatic order of the mechanism proposed by
McLerran-Shaposhnikov-Turok-Voloshin where the scalar-scalar-vector triangle
diagram with top quark in the loop gives rise to a significant contribution to
the effective chemical potential biasing the Chern-Simons number. We also show
that in 2HDM with less stringent constraints on Yukawa couplings than those
imposed by natural flavour conservation, there are additional diagrams
contributing to the effective chemical potential. These two effects can combine
with several others to produce adequate baryon asymmetry at the electroweak
scale.Comment: 7 pages, Latex, figures available upon reques
Cosmic Strings at the Electroweak Phase Transition
If cosmic strings are present at the electroweak phase transition, they can
act as seeds on which bubbles of true vacuum nucleate. We explore the nature of
such a phase transition, in particular the wall velocity and thickness of the
bubbles. {}From the viewpoint of electroweak baryogenesis, adiabatic conditions
exist in the expanding bubble walls, and such models of baryogenesis can be
successfully applied. In the present mechanism, the nature of the electroweak
phase transition is insensitive to the other details of the model, thus
reducing the uncertainties in the estimate of net baryon asymmetry.Comment: 11 Pages (figure available on request
Baryogenesis
Developments in understanding of Baryogenesis are reviewed. We start with early motivations and the proposals in the context of GUTs. Next, the importance of the sphaleron solution and its implications are discussed. Studies of the Standard Model reveal that the latter has a Higgs structure incompatible with existence of observed \B asymmetry. We then discuss a generic scenario for electroweak baryogenesis relying on bubble wall dynamics. We also summarise the status of the MSSM, and alternative scenarios utilising topological defects as the source of non-equilibrium behaviour and leptogenesis
B-L Cosmic strings and Baryogenesis
Cosmic strings arising from breaking of the gauge symmetry that
occurs in a wide variety of unified models can carry zero modes of heavy
Majorana neutrinos. Decaying and/or repeatedly self-interacting closed loops of
these ``'' cosmic strings can be a non-thermal source of heavy
right-handed Majorana neutrinos whose decay can contribute to the observed
baryon asymmetry of the Universe (BAU) via the leptogenesis route. The
cosmic strings are expected in GUT models such as SO(10), where they can be
formed at an intermediate stage of symmetry breaking well below the GUT scale
GeV; such light strings are not excluded by the CMB anisotropy
data and may well exist. We estimate the contribution of cosmic string
loops to the baryon-to-photon ratio of the Universe in the light of current
knowledge on neutrino masses and mixings implied by atmospheric and solar
neutrino measurements. We find that cosmic string loops can contribute
significantly to the BAU for symmetry breaking scale
\eta_{B-L}\gsim 1.7\times 10^{11}\gev. At the same time, in order for the
contribution of decaying cosmic string loops not to exceed the observed
baryon-to-photon ratio inferred from the recent WMAP results, the lightest
heavy right-handed Majorana neutrino mass must satisfy the constraint
M_1 \leq 2.4 \times 10^{12}(\eta_{B-L}/10^{13}\gev)^{1/2}\gev. This may have
interesting implications for the associated Yukawa couplings in the heavy
neutrino sector and consequently for the light neutrino masses generated
through see-saw mechanism.Comment: match with the published versio
Baryogenesis at the electroweak scale
The realisation that the electroweak anomaly can induce significant baryon number violation at high temperature and that the standard models of particle physics and cosmology contain all the ingredients needed for baryogenesis has led to vigourous search for viable models. The conclusions so far are that the Standard Model of particle physics cannot produce baryon asymmetry of required magnitude. It has too little CP violation and sphaleronic transitions wipe out any asymmetry produced if the Higgs is heavier than about 50 GeV, a range already excluded by accelerator experiments. We review the sphaleron solution, its connection to the high temperature anomalous rate and then summarise possibilities where phenomenologically testable extensions of the Standard Model may yet explain the baryon asymmetry of the Universe
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