3,756 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
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
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
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 , and , the 's freeze out at a higher temperature
and have a larger relic density than 's. If m_X \lsi 4.5 B_X GeV and the
annihilation cross sections differ by (10%) or more, this type of
scenario naturally explains the observed . Two
concrete examples are given, one of which can be excluded on observational
grounds
Relating multihadron production in hadronic and nuclear collisions
The energy-dependence of charged particle mean multiplicity and
pseudorapidity density at midrapidity measured in nucleus-nucleus and
(anti)proton-proton collisions are studied in the entire available energy
range. The study is performed using a model, which considers the multiparticle
production process according to the dissipating energy of the participants and
their types, namely a combination of the constituent quark picture together
with Landau relativistic hydrodynamics. The model reveals interrelations
between the variables under study measured in nucleus-nucleus and
nucleon-nucleon collisions. Measurements in nuclear reactions are shown to be
well reproduced by the measurements in (anti)proton-proton interactions common
and the corresponding fits are presented. Different observations in other types
of collisions are discussed in the framework of the proposed model. Predictions
are made for measurements at the forthcoming LHC energies.Comment: Europ. Phys. J. C (to appear). Recently CMS reported
(arXiv:1005.3299) on the midrapidity density value of 5.78 +/- 0.01(stat) +/-
0.23(syst) in pp collisons at 7 TeV, which agrees well with the value of 5.8
of our prediction
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)
Antimatter regions in the baryon-dominated Universe
Quantum fluctuations of a complex, baryonic charged scalar field caused by
inflation can generate large domains, which convert later into antimatter
regions. As a result the Universe can become globally matter-dominated, with
minor contribution of antimatter regions. The distribution and evolution of
such antimatter regions could cause every galaxy to be a harbour of an
anti-star globular cluster. At the same time, the scenario does not lead to
large-scale isocuvature perturbations, which would disturb observable CMB
anisotropy. The existence of one of such antistar globular cluster in our
Galaxy does not contradict the observed -ray background, but the
expected fluxes of and from such an
antimatter object are definitely accessible to the sensitivity of the coming
AMS--02 experiment.Comment: Talk given at the XIVth Rencontres de Blois 2002 on Matter-Antimatter
Asymmetry, Blois, France, June, 2002, to be published in the proceedings, ed.
J. Tran Thanh Van, 4 latex pages, 2 eps figure
Possible Origin of Antimatter Regions in the Baryon Dominated Universe
We discuss the evolution of U(1) symmetric scalar field at the inflation
epoch with a pseudo Nambu-Goldstone tilt revealing after the end of exponential
expansion of the Universe. The U(1) symmetry is supposed to be associated with
baryon charge. It is shown that quantum fluctuations lead in natural way to
baryon dominated Universe with antibaryon excess regions. The range of
parameters is calculated at which the fraction of Universe occupied by
antimatter and the size of antimatter regions satisfy the observational
constraints, survive to the modern time and lead to effects, accessible to
experimental search for antimatter.Comment: 10 pages, 1 figur
- …