716 research outputs found
Neutrino Masses and GUT Baryogenesis
We reconsider the GUT-baryogenesis mechanism for generating the baryon
asymmetry of the Universe. The baryon asymmetry is produced by the out of
equilibrium decay of coloured Higgs bosons at the GUT scale, conserving B-L. If
neutrinos are Majorana particles, lepton number violating interactions erase
the lepton number excess, but part of the baryon asymmetry may be preserved,
provided those interactions are not in thermal equilibrium when the sphaleron
processes become effective, at . We analyse whether this
mechanism for baryogenesis is feasible in a variety of GUT models of fermion
masses proposed in the literature, based on horizontal symmetries.Comment: Talk presented at AHEP2003, Valencia, Spain, October 200
Differential Regularization of a Non-relativistic Anyon Model
Differential regularization is applied to a field theory of a
non-relativistic charged boson field with
self-interaction and coupling to a statistics-changing Chern-Simons
gauge field. Renormalized configuration-space amplitudes for all diagrams
contributing to the 4-point function, which
is the only primitively divergent Green's function, are obtained up to 3-loop
order. The renormalization group equations are explicitly checked, and the
scheme dependence of the -function is investigated. If the
renormalization scheme is fixed to agree with a previous 1-loop calculation,
the 2- and 3-loop contributions to vanish, and
itself vanishes when the ``self-dual'' condition relating
to the gauge coupling is imposed.Comment: 22 pages in ReVTEX (with a plaintext PostScript figure appended at
end), MIT CTP #221
Symmetry Non-restoration at High Temperature
We discuss the (non)-restoration of global and local symmetries at high
temperature. First, we analyze a two-scalar model with
symmetry using the exact renormalization group. We conclude that inverse
symmetry breaking is possible in this kind of models within the perturbative
regime. Regarding local symmetries, we consider the gauge
symmetry and focus on the case of a strongly interacting scalar sector.
Employing a model-independent chiral Lagrangian we find indications of symmetry
restoration.Comment: 8 pages, LaTex with sprocl.sty, 1 figure. To appear in the
Proceedings of the International Workshop ``Beyond the Standard Model: from
Theory to Experiment'
Can new generations explain neutrino masses?
In this talk we explore the possibility that the smallness of the observed
neutrino masses is naturally understood in a modified version of the standard
model with N extra generations of fermions and N right-handed neutrinos, in
which light neutrino masses are generated at two loops. We find that with N = 1
it is not possible to fit the observed spectrum of masses and mixings while
with N = 2 it is. Within this extension, we analyse the parameters which are
allowed and the possible phenomenological signals of the model in future
experiments. Contribution to the proceedings of Les Rencontres de Moriond EW
2011, Young Scientist Forum
Selective epitaxial growth of graphene on SiC
We present an innovative method of selective epitaxial growth of few layers
graphene (FLG) on a pre-patterned SiC substrate. The methods involves,
successively, the sputtering of a thin AlN layer on top of a mono-crystalline
SiC substrate and, then, patterning it with e-beam lithography (EBL) and wet
etching. The sublimation of few atomic layers of Si from the SiC substrate
occurs only through the selectively etched AlN layer. The presence of the Raman
G-band at ~1582 cm-1 in the AlN-free areas is used to validate the concept, it
gives absolute evidence of the selective FLG growth.Comment: comments: 3 pages, reference 3 replace
Surface MIMO: Using Conductive Surfaces For MIMO Between Small Devices
As connected devices continue to decrease in size, we explore the idea of
leveraging everyday surfaces such as tabletops and walls to augment the
wireless capabilities of devices. Specifically, we introduce Surface MIMO, a
technique that enables MIMO communication between small devices via surfaces
coated with conductive paint or covered with conductive cloth. These surfaces
act as an additional spatial path that enables MIMO capabilities without
increasing the physical size of the devices themselves. We provide an extensive
characterization of these surfaces that reveal their effect on the propagation
of EM waves. Our evaluation shows that we can enable additional spatial streams
using the conductive surface and achieve average throughput gains of 2.6-3x for
small devices. Finally, we also leverage the wideband characteristics of these
conductive surfaces to demonstrate the first Gbps surface communication system
that can directly transfer bits through the surface at up to 1.3 Gbps.Comment: MobiCom '1
Predicting the baryon asymmetry with degenerate right-handed neutrinos
We consider the generation of a baryon asymmetry in an extension of the
Standard Model with two singlet Majorana fermions that are degenerate above the
electroweak phase transition. The model can explain neutrino masses as well as
the observed matter-antimatter asymmetry, for masses of the heavy singlets
below the electroweak scale. The only physical CP violating phases in the model
are those in the PMNS mixing matrix, i.e. the Dirac phase and a Majorana phase
that enter light neutrino observables. We present an accurate analytic
approximation for the baryon asymmetry in terms of CP flavour invariants, and
derive the correlations with neutrino observables. We demonstrate that the
measurement of CP violation in neutrino oscillations as well as the mixings of
the heavy neutral leptons with the electron, muon and tau flavours suffice to
pin down the matter-antimatter asymmetry from laboratory measurements.Comment: 29 + 4 pages, 9 figures. Includes a comparison to the non-degenerate
scenario. Matches published version in JHE
The Fading of Symmetry Non-restoration at Finite Temperature
The fate of symmetries at high temperature determines the dynamics of the
very early universe. It is conceivable that temperature effects favor symmetry
breaking instead of restoration. Concerning global symmetries, the non-linear
sigma model is analyzed in detail. For spontaneously broken gauge symmetries,
we propose the gauge boson magnetic mass as a ``flag'' for symmetry
(non)-restoration. We consider several cases: the standard model with one and
two Higgs doublets in the perturbative regime, and the case of a strongly
interacting Higgs sector. The latter is done in a model independent way with
the tools provided by chiral Lagrangians. Our results clearly point towards
restoration, a pattern consistent with recent lattice computations for global
symmetries. In addition, we explicitly verify invariance for gauge
theories at finite temperature.Comment: 28 pages, Latex2e, 28 figures, two typos corrected, conclusions
remain unchange
Inverse Symmetry Breaking and the Exact Renormalization Group
We discuss the question of inverse symmetry breaking at non-zero temperature
using the exact renormalization group. We study a two-scalar theory and
concentrate on the nature of the phase transition during which the symmetry is
broken. We also examine the persistence of symmetry breaking at temperatures
higher than the critical one.Comment: 8 pages, 4 figure
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