3,558 research outputs found
Supersymmetric SO(10) Grand Unification at the LHC and Beyond
We study models of supersymmetric grand unification based on the SO(10) gauge
group. We investigate scenarios of non-universal gaugino masses including
models containing a mixture of two representations of hidden sector chiral
superfields. We analyse the effect of excluding mu from the fine-tuning
measure, and confront the results with low energy constraints, including the
Higgs boson mass, dark matter relic density and supersymmetry bounds. We also
determine high scale Yukawa coupling ratios and confront the results with
theoretical predictions. Finally, we present two additional benchmarks that
should be explored at the LHC and future colliders.Comment: Published versio
Neutrino masses from new generations
We reconsider the possibility that Majorana masses for the three known
neutrinos are generated radiatively by the presence of a fourth generation and
one right-handed neutrino with Yukawa couplings and a Majorana mass term. We
find that the observed light neutrino mass hierarchy is not compatible with low
energy universality bounds in this minimal scenario, but all present data can
be accommodated with five generations and two right-handed neutrinos. Within
this framework, we explore the parameter space regions which are currently
allowed and could lead to observable effects in neutrinoless double beta decay,
conversion in nuclei and experiments. We
also discuss the detection prospects at LHC.Comment: 28 pages, 4 figures. Version to be published. Some typos corrected.
Improved figures 3 and
Solar internal rotation rate and the latitudinal variation of the tachocline
A new set of accurately measured frequencies of solar oscillations are used
to infer the rotation rate inside the Sun, as a function of radial distance as
well as latitude. We have adopted a regularized least squares technique with
iterative refinement for both 1.5D inversion using the splitting coefficients
and 2D inversion using individual m splittings. The inferred rotation rate
agrees well with earlier estimates showing a shear layer just below the surface
and another one around the base of the convection zone. The tachocline or the
transition layer where the rotation rate changes from differential rotation in
the convection zone to almost latitudinally independent rotation rate in the
radiative interior is studied in detail. No compelling evidence for any
latitudinal variation in position and width of tachocline is found though it
appears that the tachocline probably shifts to slightly larger radial distance
at higher latitudes and possibly becomes thicker also. However, these
variations are within the estimated errors and more accurate data would be
needed to make a definitive statement about latitudinal variations.Comment: 15 pages, MNRAS-TeX, 15 figure
Supersymmetric model of quasi-degenerate neutrinos
We present a supersymmetric model of fermion masses, based on a non-Abelian
family symmetry and the Froggatt-Nielsen mechanism, that can account for the
solar and atmospheric neutrino problems via quasi-degenerate neutrinos. The
model predicts that the ratio of neutrino mass squared splittings \Delta
m^2_{12} / \Delta m^2_{23} is of order m_s^2/m_b^2, and the angles \theta_{12}
\sim m_d/m_s and \theta_{23} \sim 1, which are of the desired orders of
magnitude. We discuss the implications of the flavor structure of the neutrino
sector on superparticle masses and mixing angles.Comment: 14 pages LaTeX, two EPS figure
symmetry at colliders and in the universe
Two puzzling facts of our time are the observed patterns in the fermion
masses and mixings and the existence of non-baryonic dark matter, which are
both often associated with extensions of the Standard Model at higher energy
scales. In this paper, we consider a solution to these two problems with the
flavour symmetry , in a model which has been shown before to explain large leptonic
mixings with a specific texture. The model contains 3 generations of
-doublet scalar fields, arranged as an -triplet, that
spontaneously break the electroweak symmetry, and a "dark sector" of -odd fields, containing one Majorana neutrino and an -triplet -doublet scalar field, the lightest of which provides a
candidate for dark matter.
Concerning the -even scalar fields, compared to the Standard
Model, we predict additional fields with masses at the electroweak scale. We
therefore investigate present phenomenological constraints from lepton flavour
violation experiments, obtaining a lower bound on the extra scalar masses of
140 GeV. Furthermore we consider the oblique parameters, Higgs boson decay
properties and possible flavour violating signals at the LHC.
Concerning the "dark sector", we study bounds from dark matter search
experiments and identify the parameter space of the dark matter candidate that
is compatible with the observed relic density. We find two allowed mass ranges
for the dark matter within which the experimental constraints can be
accommodated: the low-mass range is from 47 GeV to 74 GeV and the high-mass
range is from 600 GeV and 3.6 TeV.Comment: v2, to be published in JHE
LHC Searches for Non-Chiral Weakly Charged Multiplets
Because the TeV-scale to be probed at the Large Hadron Collider should shed
light on the naturalness, hierarchy, and dark matter problems, most searches to
date have focused on new physics signatures motivated by possible solutions to
these puzzles. In this paper, we consider some candidates for new states that
although not well-motivated from this standpoint are obvious possibilities that
current search strategies would miss. In particular we consider vector
representations of fermions in multiplets of with a lightest neutral
state. Standard search strategies would fail to find such particles because of
the expected small one-loop-level splitting between charged and neutral states.Comment: 16 pages, 9 figure
Fermion Masses and Mixing in Extended Technicolor Models
We study fermion masses and mixing angles, including the generation of a
seesaw mechanism for the neutrinos, in extended technicolor (ETC) theories. We
formulate an approach to these problems that relies on assigning right-handed
quarks and charged leptons to ETC representations that are conjugates
of those of the corresponding left-handed fermions. This leads to a natural
suppression of these masses relative to the quarks, as well as the
generation of quark mixing angles, both long-standing challenges for ETC
theories. Standard-model-singlet neutrinos are assigned to ETC representations
that provide a similar suppression of neutrino Dirac masses, as well as the
possibility of a realistic seesaw mechanism with no mass scale above the
highest ETC scale of roughly TeV. A simple model based on the ETC group
SU(5) is constructed and analyzed. This model leads to non-trivial, but not
realistic mixing angles in the quark and lepton sectors. It can also produce
sufficiently light neutrinos, although not simultaneously with a realistic
quark spectrum. We discuss several aspects of the phenomenology of this class
of models.Comment: 74 pages, revtex with embedded figure
Schwarz Iterative Methods: Infinite Space Splittings
We prove the convergence of greedy and randomized versions of Schwarz
iterative methods for solving linear elliptic variational problems based on
infinite space splittings of a Hilbert space. For the greedy case, we show a
squared error decay rate of for elements of an approximation
space related to the underlying splitting. For the randomized
case, we show an expected squared error decay rate of on a
class depending on the
probability distribution.Comment: Revised version, accepted in Constr. Appro
Electroweak Multiplet Dark Matter at Future Lepton Colliders
An electroweak multiplet stable due to a new global symmetry is a simple and
well-motivated candidate for thermal dark matter. We study how direct searches
at a future linear collider, such as the proposed CLIC, can constrain scalar
and fermion triplets, quintets and septets, as well as a fermion doublet. The
phenomenology is highly sensitive to charged state lifetimes and thus the mass
splitting between the members of the multiplet. We include both radiative
corrections and the effect of non-renormalisable operators on this splitting.
In order to explore the full range of charged state lifetimes, we consider
signals including long-lived charged particles, disappearing tracks, and
monophotons. By combining the different searches we find discovery and
exclusion contours in the mass-lifetime plane. In particular, when the mass
splitting is generated purely through radiative corrections, we can exclude the
pure-Higgsino doublet below 310 GeV, the pure-wino triplet below 775 GeV, and
the minimal dark matter fermion quintet below 1025 GeV. The scenario where the
thermal relic abundance of a Higgsino accounts for the whole dark matter of the
Universe can be excluded if the mass splitting between the charged and neutral
states is less than 230 MeV. Finally, we discuss possible improvements to these
limits by using associated hard leptons to idenify the soft visible decay
products of the charged members of the dark matter multiplet.Comment: 24 pages, 14 figures; version 2, additional reference
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