4,148 research outputs found
Phenomenology of Dirac Neutrinogenesis in Split Supersymmetry
In Split Supersymmetry scenarios the possibility of having a very heavy
gravitino opens the door to alleviate or completely solve the worrisome
"gravitino problem'' in the context of supersymmetric baryogenesis models. Here
we assume that the gravitino may indeed be heavy and that Majorana masses for
neutrinos are forbidden as well as direct Higgs Yukawa couplings between left
and right handed neutrinos. We investigate the viability of the mechansim known
as Dirac leptogenesis (or neutrinogenesis), both in solving the baryogenesis
puzzle and explaining the observed neutrino sector phenomenology. To
successfully address these issues, the scenario requires the introduction of at
least two new heavy fields. If a hierarchy among these new fields is
introduced, and some reasonable stipulations are made on the couplings that
appear in the superpotential, it becomes a generic feature to obtain the
observed large lepton mixing angles. We show that in this case, it is possible
simultaneously to obtain both the correct neutrino phenomenology and enough
baryon number, making thermal Dirac neutrinogenesis viable. However, due to
cosmological constraints, its ability to satisfy these constraints depends
nontrivially on model parameters of the overall theory, particularly the
gravitino mass. Split supersymmetry with m_{3/2} between 10^{5} and 10^{10} GeV
emerges as a "natural habitat" for thermal Dirac neutrinogenesis.Comment: 37 pages, 8 figure
Light Stop Searches at the LHC in Events with two b-Jets and Missing Energy
We propose a new method to discover light top squarks (stops) in the
co-annihilation region at the Large Hadron Collider (LHC). The bino-like
neutralino is the lightest supersymmetric particle (LSP) and the lighter stop
is the next-to-LSP. Such scenarios can be consistent with electroweak
baryogenesis and also with dark matter constraints. We consider the production
of two stops in association with two b-quarks, including pure QCD as well as
mixed electroweak-QCD contributions. The stops decay into a charm quark and the
LSP. For a higgsino-like light chargino the electroweak contributions can
exceed the pure QCD prediction. We show the size of the electroweak
contributions as a function of the stop mass and present the LHC discovery
reach in the stop-neutralino mass plane.Comment: 12 pages, 10 figure
Leptonic CP violation studies at MiniBooNE in the (3+2) sterile neutrino oscillation hypothesis
We investigate the extent to which leptonic CP-violation in (3+2) sterile
neutrino models leads to different oscillation probabilities for
and oscillations at
MiniBooNE. We are using a combined analysis of short-baseline (SBL) oscillation
results, including the LSND and null SBL results, to which we impose additional
constraints from atmospheric oscillation data. We obtain the favored regions in
MiniBooNE oscillation probability space for both (3+2) CP-conserving and (3+2)
CP-violating models. We further investigate the allowed CP-violation phase
values and the MiniBooNE reach for such a CP violation measurement. The
analysis shows that the oscillation probabilities in MiniBooNE neutrino and
antineutrino running modes can differ significantly, with the latter possibly
being as much as three times larger than the first. In addition, we also show
that all possible values of the single CP-violation phase measurable at short
baselines in (3+2) models are allowed within 99% CL by existing data.Comment: Fixed a typo following PRD Erratum. 8 pages, 5 figure
Gravitational waves from first order phase transitions during inflation
We study the production, spectrum and detectability of gravitational waves in
models of the early Universe where first order phase transitions occur during
inflation. We consider all relevant sources. The self-consistency of the
scenario strongly affects the features of the waves. The spectrum appears to be
mainly sourced by collisions of bubble of the new phases, while plasma dynamics
(turbulence) and the primordial gauge fields connected to the physics of the
transitions are generally subdominant. The amplitude and frequency dependence
of the spectrum for modes that exit the horizon during inflation are different
from those of the waves produced by quantum vacuum oscillations of the metric
or by first order phase transitions not occurring during inflation. A moderate
number of slow (but still successful) phase transitions can leave detectable
marks in the CMBR, but the signal weakens rapidly for faster transitions. When
the number of phase transitions is instead large, the primordial gravitational
waves can be observed both in the CMBR or with LISA (marginally) and especially
DECIGO. We also discuss the nucleosynthesis bound and the constraints it places
on the parameters of the models.Comment: minor changes in the text and the references to match the published
versio
Leptogenesis from Gravity Waves in Models of Inflation
We present a new mechanism for creating the observed cosmic matter-antimatter
asymmetry which satisfies all three Sakharov conditions from one common thread,
gravitational waves. We generate lepton number through the gravitational
anomaly in the lepton number current. The source term comes from elliptically
polarizated gravity waves that are produced during inflation if the inflaton
field contains a CP-odd component. In simple inflationary scenarios, the
generated matter asymmetry is very small. We describe some special conditions
in which our mechanism can give a matter asymmetry of realistic size.Comment: 4 pages, RevTeX4.1 format; an error in computations correcte
Generating the Baryon Asymmetry of the Universe in Split Fermion Models
The origin of the matter-antimatter asymmetry of the universe is one of the
major unsolved problems in cosmology and particle physics. In this paper, we
investigate the recently proposed possibility that split fermion models --
extra dimensional models where the standard model fermions are localized to
different points around the extra dimension -- could provide a means to
generate this asymmetry during the phase transition of the localizing scalars.
After setting up the scenario that we consider, we use a single fermion toy
model to estimate the reflection coefficients for scattering off the phase
boundary using a more realistic scalar profile than previous work resulting in
a different Kaluza Klein spectrum. The value we calculate for is
consistent with the mechanism being the source of the baryon asymmetry of our
universe provided the violating processes have an efficiency of order
.Comment: 17 pages, 3 figures; References added; Minor changes, Accepted for
publication in Phys. Rev.
Leptogenesis in models with keV sterile neutrino dark matter
We analyze leptogenesis in gauge extensions of the Standard Model with keV
sterile neutrino dark matter. We find that both the observed dark matter
abundance and the correct baryon asymmetry of the Universe can simultaneously
emerge in these models. Both the dark matter abundance and the leptogenesis are
controlled by the out of equilibrium decays of the same heavy right handed
neutrino.Comment: 6 pages, 1 figur
Gravitational baryogenesis in Gauss-Bonnet braneworld cosmology
The mechanism of gravitational baryogenesis, based on the CPT-violating
gravitational interaction between the derivative of the Ricci scalar curvature
and the baryon-number current, is investigated in the context of the
Gauss-Bonnet braneworld cosmology. We study the constraints on the fundamental
five-dimensional gravity scale, the effective scale of B-violation and the
decoupling temperature, for the above mechanism to generate an acceptable
baryon asymmetry during the radiation-dominated era. The scenario of
gravitational leptogenesis, where the lepton-number violating interactions are
associated with the neutrino mass seesaw operator, is also considered.Comment: 8 pages, 3 figures, final version to appear in Phys. Rev.
Remarks on the hadronic matrix elements relevant to the SUSY K-Kbar mixing amplitude
We compute the 1-loop chiral corrections to the bag parameters which are
needed for the discussion of the SUSY K-Kbar mixing problem in both finite and
infinite volume. We then show how the bag parameters can be combined among
themselves and with some auxiliary quantities and thus sensibly reduce the
systematic errors due to chiral extrapolations as well as those due to finite
volume artefacts present in the results obtained from lattice QCD. We also show
that in some cases these advantages remain as such even after including the
2-loop chiral corrections. Similar discussion is also made for the K --> pi
electro-weak penguin operators.Comment: 13 pages, 3 figures [added 1 reference and a discussion about the
impact of the NNLO chiral corrections to the "golden ratios" (c.f. Sec.6)
Signatures from an extra-dimensional seesaw model
We study the generation of small neutrino masses in an extra-dimensional
model, where right-handed neutrinos are allowed to propagate in the extra
dimension, while the Standard Model particles are confined to a brane.
Motivated by the fact that extra-dimensional models are non-renormalizable, we
truncate the Kaluza-Klein towers at a maximal extra-dimensional momentum. The
structure of the bulk Majorana mass term, motivated by the Sherk-Schwarz
mechanism, implies that the right-handed Kaluza-Klein neutrinos pair to form
Dirac neutrinos, except for a number of unpaired Majorana neutrinos at the top
of each tower. These heavy Majorana neutrinos are the only sources of lepton
number breaking in the model, and similarly to the type-I seesaw mechanism,
they naturally generate small masses for the left-handed neutrinos. The lower
Kaluza-Klein modes mix with the light neutrinos, and the mixing effects are not
suppressed with respect to the light-neutrino masses. Compared to conventional
fermionic seesaw models, such mixing can be more significant. We study the
signals of this model at the Large Hadron Collider, and find that the current
low-energy bounds on the non-unitarity of the leptonic mixing matrix are strong
enough to exclude an observation.Comment: 17 pages, 3 figures, REVTeX4. Final version published in Phys. Rev.
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