4,623 research outputs found

### Lepton Flavor Violation and Supersymmetric Dirac Leptogenesis

Dirac leptogenesis (or Dirac neutrinogenesis), in which neutrinos are purely
Dirac particles, is an interesting alternative to the standard leptogenesis
scenario. In its supersymmetric version, the modified form of the
superpotential required for successful baryogenesis contributes new,
generically non-flavor-diagonal terms to the slepton and sneutrino mass
matrices. In this work, we examine how current experimental bounds on
flavor-changing effects in the lepton sector (and particularly the bound on Mu
-> e Gamma) constrain Dirac leptogenesis and we find that it is capable of
succeeding with superpartner masses as low as 100 GeV. For such light scalars
and electroweakinos, upcoming experiments such as MEG are generically expected
to observe signals of lepton flavor violation.Comment: 15 pages, 4 figures, corrected parametric dependance on leading LFV
term, figure 2 and discussion modified accordingly, conclusions unchange

### Baryogenesis and Late-Decaying Moduli

Late-decaying string moduli dilute the baryon asymmetry of the universe
created in any previous era. The reheat temperature for such moduli is below a
GeV, thus motivating baryogenesis at very low temperatures. We present an
extension of the minimal supersymmetric standard model with TeV-scale colored
fields that can yield the correct baryon asymmetry of the universe in this
context. Modulus decay, which reheats the universe at a temperature below GeV,
produces the visible sector fields and neutralino dark matter in non-thermal
fashion. We discuss various possibilities for baryogenesis from TeV scale
colored fields and show that they can generate an acceptable baryon asymmetry,
while being compatible with phenomenological constraints like
neutron-antineutron oscillation.Comment: 8 pages, 3 figure

### Hierarchy from Baryogenesis

We study a recently proposed mechanism to solve the hierarchy problem in the
context of the landscape, where the solution of the hierarchy problem is
connected to the requirement of having baryons in our universe via Electroweak
Baryogenesis. The phase transition is triggered by the fermion condensation of
a new gauge sector which becomes strong at a scale Lambda determined by
dimensional transmutation, and it is mediated to the standard model by a new
singlet field. In a ``friendly'' neighborhood of the landscape, where only the
relevant operators are ``scanned'' among the vacua, baryogenesis is effective
only if the higgs mass m_h is comparable to this low scale Lambda, forcing m_h
to be of order Lambda, and solving the hierarchy problem. A new CP violating
phase is needed coupling the new singlet and the higgs field to new matter
fields. We study the constraints on this model given by baryogenesis and by the
electron electric dipole moment (EDM), and we briefly comment on gauge coupling
unification and on dark matter relic abundance. We find that next generation
experiments on the EDM will be sensitive to essentially the entire viable
region of the parameter space, so that absence of a signal would effectively
rule out the model.Comment: 28 pages, 4 figures. v2: Added comments and references. Corrected one
typo in eq.(81). Conclusions unaltere

### Higgs Boson Exempt No-Scale Supersymmetry with a Neutrino Seesaw: Implications for Lepton Flavor Violation and Leptogenesis

Motivated by the observation of neutrino oscillations, we extend the Higgs
boson exempt no-scale supersymmetry model (HENS) by adding three heavy
right-handed neutrino chiral supermultiplets to generate the light neutrino
masses and mixings. The neutrino Yukawa couplings can induce new lepton flavor
violating couplings among the soft terms in the course of renormalization group
running down from the boundary scale. We study the effects this has on the
predictions for low-energy probes of lepton flavor violation(LFV). Heavy
right-handed neutrinos also provide a way to generate the baryon asymmetry
through leptogenesis. We find that consistency with LFV and leptogenesis puts
strong requirements on either the form of the Yukawa mass matrix or the
smallness of the Higgs up soft mass. In all cases, we generically expect that
new physics LFV is non-zero and can be found in a future experiment.Comment: 25 pages, 11 figures; Added a referenc

### 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

### Baryon Number Violation Involving Higher Generations

Proton stability seems to constrain rather strongly any baryon number
violating process. We investigate the possibility of baryon number violating
processes involving right-handed dynamics or higher generation quarks. Our
results strongly suggest that there will be no possibility to observe baryon
number violation in tau or higher generation quark decays, at any future
machine.Comment: Improved figures, small changes in the text, added reference. To
appear in Phys. Rev.

### CP Violation in Fourth Generation Quark Decays

We show that, if a fourth generation is discovered at the Tevatron or LHC,
one could study CP violation in b' \to s decays. Asymmetries could reach 30%
for b'\to sZ for m_{b'} \lesssim 350 GeV, while it could be greater than 50%
for b'\to s\gamma and extend to higher m_{b'}. Branching ratios are
10^{-3}--10^{-5}, and CPV measurement requires tagging. Once measured, however,
the CPV phase can be extracted with little theoretical uncertainty.Comment: 4 pages, 7 eps 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

### Dark Matter and the Baryon Asymmetry

We present a mechanism to generate the baryon asymmetry of the Universe which
preserves the net baryon number created in the Big Bang. If dark matter
particles carry baryon number $B_X$, and $\sigma^{\rm annih}_{\bar{X}} <
\sigma^{\rm annih}_{X}$, the $\bar{X}$'s freeze out at a higher temperature
and have a larger relic density than $X$'s. If m_X \lsi 4.5 B_X GeV and the
annihilation cross sections differ by $\mathcal{O}$(10%) or more, this type of
scenario naturally explains the observed $\Omega_{DM} \approx 5 \Omega_b$. Two
concrete examples are given, one of which can be excluded on observational
grounds

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