106 research outputs found
Vacuum oscillations of quasi degenerate solar neutrinos
The atmospheric neutrino oscillations and the vacuum oscillation solution of
the solar neutrino problem can be consistently described by a doubly or triply
degenerate neutrino spectrum as long as the high level of degeneracy required
is not spoiled by radiative corrections. We show that this is the case for
neutrino mass matrices generated by symmetries. This imposes a strong
constraint on the mixing angles and requires the mixing should be close to
bi-maximal. We briefly discuss the relevance of our results for the
measurability of the neutrino spectrum.Comment: 6 pages. Final version, more clear presentatio
Epsilon' from supersymmetry with non universal A terms?
In supersymmetric theories with a motivated flavour structure, we investigate
the possibility that an epsilon' parameter as large as the measured value be
generated without conflicting with the bounds from electron and neutron
electric dipoles and mu --> e gamma.Comment: 8 pages. v2: we have cancelled hep-ph/9510303 as a motivation for non
universal A terms, because it is wrong. v3,4: A significant sign error
corrected. Conclusions unchange
Oscillations of solar and atmospheric neutrinos
Motivated by recent results from SuperKamiokande, we study both solar and
atmospheric neutrino fluxes in the context of oscillations of the three known
neutrinos. We aim at a global view which identifies the various possibilities,
rather than attempting the most accurate determination of the parameters of
each scenario. For solar neutrinos we emphasise the importance of performing a
general analysis, independent of any particular solar model and we consider the
possibility that any one of the techniques --- chlorine, gallium or water
Cerenkov --- has a large unknown systematic error, so that its results should
be discarded. The atmospheric neutrino anomaly is studied by paying special
attention to the ratios of upward and downward going nu_e and nu_mu fluxes.
Both anomalies can be described in a minimal scheme where the respective
oscillation frequencies are widely separated or in non-minimal schemes with two
comparable oscillation frequencies. We discuss explicit forms of neutrino mass
matrices in which both atmospheric and solar neutrino fluxes are explained. In
the minimal scheme we identify only two `zeroth order' textures that can result
from unbroken symmetries. Finally we discuss experimental strategies for the
determination of the various oscillation parameters.Comment: 20 pages, 7 figures. Final version: one reference added; fit of
atmospheric neutrinos improve
Anthropic solution to the magnetic muon anomaly: the charged see-saw
We present models of new physics that can explain the muon g-2 anomaly in
accord with with the assumption that the only scalar existing at the weak scale
is the Higgs, as suggested by anthropic selection. Such models are dubbed
"charged see-saw" because the muon mass term is mediated by heavy leptons. The
electroweak contribution to the g-2 gets modified by order one factors, giving
an anomaly of the same order as the observed hint, which is strongly correlated
with a modification of the Higgs coupling to the muon.Comment: 21 pages, many equations despite the first word in the title. v3:
loop function G_WN corrected, conclusions unchange
Phenomenology of a Fluxed MSSM
We analyze the phenomenology of a set of minimal supersymmetric standard
model (MSSM) soft terms inspired by flux-induced supersymmetry (SUSY)-breaking
in Type IIB string orientifolds. The scheme is extremely constrained with
essentially only two free mass parameters: a parameter M, which sets the scale
of soft terms, and the mu parameter. After imposing consistent radiative
electro-weak symmetry breaking (EWSB) the model depends upon one mass parameter
(say, M). In spite of being so constrained one finds consistency with EWSB
conditions. We demonstrate that those conditions have two solutions for mu<0,
and none for mu>0. The parameter tan beta results as a prediction and is
approximately 3-5 for one solution, and 25-40 for the other, depending upon M
and the top mass. We examine further constraints on the model coming from b->s
gamma, the muon g-2, Higgs mass limits and WMAP constraints on dark matter. The
MSSM spectrum is predicted in terms of the single free parameter M. The low tan
beta branch is consistent with a relatively light spectrum although it is
compatible with standard cosmology only if the lightest neutralino is unstable.
The high tan beta branch is compatible with all phenomenological constraints,
but has quite a heavy spectrum. We argue that the fine-tuning associated to
this heavy spectrum would be substantially ameliorated if an additional
relationship mu=-2M were present in the underlying theory.Comment: 18 pages, minor revision
Static Configurations of Dark Energy and Dark Matter
We study static configurations of dark matter coupled to a scalar field
responsible for the dark energy of the Universe. The dark matter is modelled as
a Fermi gas within the Thomas-Fermi approximation. The mass of the dark matter
particles is a function of the scalar field. We analyze the profile of the dark
matter halos in galaxies. In this case our framework is equivalent to the model
of the isothermal sphere. In the presence of a scalar field, the velocity of a
massive object orbiting the galaxy is not of the order of the typical velocity
of the dark matter particles, as in the conventional picture. Instead, it is
reduced by a factor that quantifies the dependence of the dark matter mass on
the scalar field. This has implications for dark matter searches. We derive new
solutions of the Einstein equations which describe compact objects composed of
dark matter. Depending on the scale of the dark matter mass, the size of these
objects can vary between microscopic scales and cosmological distances. We
determine the mass to radius relation and discuss the similarities with
conventional neutron stars and exotic astrophysical objects.Comment: 23 pages, 3 figures, minor additions to the tex
Three-flavor solar neutrino oscillations with terrestrial neutrino constraints
We present an updated analysis of the current solar neutrino data in terms of
three-flavor oscillations, including the additional constraints coming from
terrestrial neutrino oscillation searches at the CHOOZ (reactor),
Super-Kamiokande (atmospheric), and KEK-to-Kamioka (accelerator) experiments.
The best fit is reached for the subcase of two-family mixing, and the
additional admixture with the third neutrino is severely limited. We discuss
the relevant features of the globally allowed regions in the oscillation
parameter space, as well as their impact on the amplitude of possible
CP-violation effects at future accelerator experiments and on the
reconstruction accuracy of the mass-mixing oscillation parameters at the
KamLAND reactor experiment.Comment: 10 pages + 8 figure
Strong tree level unitarity violations in the extra dimensional Standard Model with scalars in the bulk
We show how the tree level unitarity violations of compactified extra
dimensional extensions of the Standard Model become much stronger when the
scalar sector is included in the bulk. This effect occurs when the couplings
are not suppressed for larger Kaluza-Klein levels, and could have relevant
consequences for the phenomenology of the next generation of colliders. We also
introduce a simple and generic formalism to obtain unitarity bounds for finite
energies, taking into account coupled channels including the towers of
Kaluza-Klein excitations.Comment: Version to appear in Phys. Rev. D Typos corrected and remarks added
to clarify figure
Bounds on Universal Extra Dimensions
We show that the bound from the electroweak data on the size of extra
dimensions accessible to all the standard model fields is rather loose. These
"universal" extra dimensions could have a compactification scale as low as 300
GeV for one extra dimension. This is because the Kaluza-Klein number is
conserved and thus the contributions to the electroweak observables arise only
from loops. The main constraint comes from weak-isospin violation effects. We
also compute the contributions to the S parameter and the vertex.
The direct bound on the compactification scale is set by CDF and D0 in the few
hundred GeV range, and the Run II of the Tevatron will either discover extra
dimensions or else it could significantly raise the bound on the
compactification scale. In the case of two universal extra dimensions, the
current lower bound on the compactification scale depends logarithmically on
the ultra-violet cutoff of the higher dimensional theory, but can be estimated
to lie between 400 and 800 GeV. With three or more extra dimensions, the cutoff
dependence may be too strong to allow an estimate.Comment: 22 pages, Latex, 1 eps figure. Published version; minor correction in
the Kaluza-Klein decompositio
Naturalness and Fine Tuning in the NMSSM: Implications of Early LHC Results
We study the fine tuning in the parameter space of the semi-constrained
NMSSM, where most soft Susy breaking parameters are universal at the GUT scale.
We discuss the dependence of the fine tuning on the soft Susy breaking
parameters M_1/2 and m0, and on the Higgs masses in NMSSM specific scenarios
involving large singlet-doublet Higgs mixing or dominant Higgs-to-Higgs decays.
Whereas these latter scenarios allow a priori for considerably less fine tuning
than the constrained MSSM, the early LHC results rule out a large part of the
parameter space of the semi-constrained NMSSM corresponding to low values of
the fine tuning.Comment: 19 pages, 10 figures, bounds from Susy searches with ~1/fb include
- …