50 research outputs found
Footprints of the Beyond in flavor physics: Possible role of the Top Two Higgs Doublet Model
The B-factories results provide an impressive confirmation of the Standard
Model (SM) description of flavor and CP violation. Nevertheless, as more data
were accumulated, deviations in the 2.5-3.5 sigma range have emerged pointing
to the exciting possibility of new CP-odd phase(s) and flavor violating
parameters in B-decays. Primarily this seems to be the case in the time
dependent CP asymmetries in penguin dominated modes (e.g. B -> phi (eta') Ks).
We discuss these and other deviations from the SM and, as an illustration of
possible new physics scenarios, we examine the role of the Top Two Higgs
Doublet Model. This is a simple extension of the SM obtained by adding second
Higgs doublet in which the Yukawa interactions of the two Higgs doublets are
assigned in order to naturally account for the large top-quark mass.
Of course, many other extensions of the Standard Model could also account for
these experimental deviations. Clearly if one takes these deviations seriously
then some new particles in the 300 GeV to few TeV with associated new CP-odd
phase(s) are needed.Comment: 40 pages, 17 figures (png format), uses pdflate
Challenging SO(10) SUSY GUTs with family symmetries through FCNC processes
We perform a detailed analysis of the SO(10) SUSY GUT model with D3 family
symmetry of Dermisek and Raby (DR). The model is specified in terms of 24
parameters and predicts, as a function of them, the whole MSSM set of
parameters at low energy scales. Concerning the SM subset of such parameters,
the model is able to give a satisfactory description of the quark and lepton
masses, of the PMNS matrix and of the CKM matrix. We perform a global fit to
the model, including flavour changing neutral current (FCNC) processes Bs -->
mu+ mu-, B --> Xs gamma, B --> Xs l+ l- and the B(d,s) - bar B(d,s) mass
differences Delta M(d,s) as well as the flavour changing (FC) process B+ -->
tau+ nu. These observables provide at present the most sensitive probe of the
SUSY mass spectrum and couplings predicted by the model. Our analysis
demonstrates that the simultaneous description of the FC observables in
question represents a serious challenge for the DR model, unless the masses of
the scalars are moved to regions which are problematic from the point of view
of naturalness and probably beyond the reach of the LHC. We emphasize that this
problem could be a general feature of SUSY GUT models with third generation
Yukawa unification and weak-scale minimal flavour violation.Comment: 1 + 37 pages, 5 figures, 11 tables. v3: minor typos fixed. Matches
JHEP published versio
Stringy Instantons and Quiver Gauge Theories
We explore contributions to the 4D effective superpotential which arise from
Euclidean D3 branes (``instantons'') that intersect space-filling D-branes.
These effects can perturb the effective field theory on the space-filling
branes by nontrivial operators composed of charged matter fields, changing the
vacuum structure in a qualitative way in some examples. Our considerations are
exemplified throughout by a careful study of a fractional brane configuration
on a del Pezzo surface.Comment: 30 pages, 4 figures; v2: reference added; v3: confusing minor error
in axion charges fixed (thanks to D. Green for pointing it out
Mixed Wino Dark Matter: Consequences for Direct, Indirect and Collider Detection
In supersymmetric models with gravity-mediated SUSY breaking and gaugino mass
unification, the predicted relic abundance of neutralinos usually exceeds the
strict limits imposed by the WMAP collaboration. One way to obtain the correct
relic abundance is to abandon gaugino mass universality and allow a mixed
wino-bino lightest SUSY particle (LSP). The enhanced annihilation and
scattering cross sections of mixed wino dark matter (MWDM) compared to bino
dark matter lead to enhanced rates for direct dark matter detection, as well as
for indirect detection at neutrino telescopes and for detection of dark matter
annihilation products in the galactic halo. For collider experiments, MWDM
leads to a reduced but significant mass gap between the lightest neutralinos so
that chi_2^0 two-body decay modes are usually closed. This means that dilepton
mass edges-- the starting point for cascade decay reconstruction at the CERN
LHC-- should be accessible over almost all of parameter space. Measurement of
the m_{\tz_2}-m_{\tz_1} mass gap at LHC plus various sparticle masses and cross
sections as a function of beam polarization at the International Linear
Collider (ILC) would pinpoint MWDM as the dominant component of dark matter in
the universe.Comment: 29 pages including 19 eps figure
Exploring the BWCA (Bino-Wino Co-Annihilation) Scenario for Neutralino Dark Matter
In supersymmetric models with non-universal gaugino masses, it is possible to
have opposite-sign SU(2) and U(1) gaugino mass terms. In these models, the
gaugino eigenstates experience little mixing so that the lightest SUSY particle
remains either pure bino or pure wino. The neutralino relic density can only be
brought into accord with the WMAP measured value when bino-wino co-annihilation
(BWCA) acts to enhance the dark matter annihilation rate. We map out parameter
space regions and mass spectra which are characteristic of the BWCA scenario.
Direct and indirect dark matter detection rates are shown to be typically very
low. At collider experiments, the BWCA scenario is typified by a small mass gap
m_{\tilde Z_2}-m_{\tilde Z_1} ~ 20-80 GeV, so that tree level two body decays
of \tilde Z_2 are not allowed. However, in this case the second lightest
neutralino has an enhanced loop decay branching fraction to photons. While the
photonic neutralino decay signature looks difficult to extract at the Fermilab
Tevatron, it should lead to distinctive events at the CERN LHC and at a linear
e^+e^- collider.Comment: 44 pages, 21 figure
Collider and Dark Matter Phenomenology of Models with Mirage Unification
We examine supersymmetric models with mixed modulus-anomaly mediated SUSY
breaking (MM-AMSB) soft terms which get comparable contributions to SUSY
breaking from moduli-mediation and anomaly-mediation. The apparent (mirage)
unification of soft SUSY breaking terms at Q=mu_mir not associated with any
physical threshold is the hallmark of this scenario. The MM-AMSB structure of
soft terms arises in models of string compactification with fluxes, where the
addition of an anti-brane leads to an uplifting potential and a de Sitter
universe, as first constructed by Kachru {\it et al.}. The phenomenology mainly
depends on the relative strength of moduli- and anomaly-mediated SUSY breaking
contributions, and on the Higgs and matter field modular weights, which are
determined by the location of these fields in the extra dimensions. We
delineate the allowed parameter space for a low and high value of tan(beta),
for a wide range of modular weight choices. We calculate the neutralino relic
density and display the WMAP-allowed regions. We show the reach of the CERN LHC
and of the International Linear Collider. We discuss aspects of MM-AMSB models
for Tevatron, LHC and ILC searches, muon g-2 and b->s \gamma branching
fraction. We also calculate direct and indirect dark matter detection rates,
and show that almost all WMAP-allowed models should be accessible to a
ton-scale noble gas detector. Finally, we comment on the potential of colliders
to measure the mirage unification scale and modular weights in the difficult
case where mu_mir>>M_GUT.Comment: 34 pages plus 42 EPS figures; version with high resolution figures is
at http://www.hep.fsu.edu/~bae
Mixed Higgsino Dark Matter from a Reduced SU(3) Gaugino Mass: Consequences for Dark Matter and Collider Searches
In gravity-mediated SUSY breaking models with non-universal gaugino masses,
lowering the SU(3) gaugino mass |M_3| leads to a reduction in the squark and
gluino masses. Lower third generation squark masses, in turn, diminish the
effect of a large top quark Yukawa coupling in the running of the higgs mass
parameter m_{H_u}^2, leading to a reduction in the magnitude of the
superpotential mu parameter (relative to M_1 and M_2). A low | mu | parameter
gives rise to mixed higgsino dark matter (MHDM), which can efficiently
annihilate in the early universe to give a dark matter relic density in accord
with WMAP measurements. We explore the phenomenology of the low |M_3| scenario,
and find for the case of MHDM increased rates for direct and indirect detection
of neutralino dark matter relative to the mSUGRA model. The sparticle mass
spectrum is characterized by relatively light gluinos, frequently with
m(gl)<<m(sq). If scalar masses are large, then gluinos can be very light, with
gl->Z_i+g loop decays dominating the gluino branching fraction. Top squarks can
be much lighter than sbottom and first/second generation squarks. The presence
of low mass higgsino-like charginos and neutralinos is expected at the CERN
LHC. The small m(Z2)-m(Z1) mass gap should give rise to a visible
opposite-sign/same flavor dilepton mass edge. At a TeV scale linear e^+e^-
collider, the region of MHDM will mean that the entire spectrum of charginos
and neutralinos are amongst the lightest sparticles, and are most likely to be
produced at observable rates, allowing for a complete reconstruction of the
gaugino-higgsino sector.Comment: 35 pages, including 26 EPS figure
Dark Matter And With Minimal Soft SUSY Breaking II
We update and extend to larger masses our previous analysis of the MSSM with
minimal [MSOSM] soft SUSY breaking boundary conditions. We
find a well--defined, narrow region of parameter space which provides the
observed relic density of dark matter, in a domain selected to fit precision
electroweak data, including top, bottom and tau masses. The model is highly
constrained which allows us to make several predictions. We find the light
Higgs mass GeV and also upper bounds on the mass of the
gluino \mgluino\lsim3.1 TeV and lightest neutralino \mchi\lsim450 GeV. As
the CP odd Higgs mass increases, the region of parameter space consistent
with WMAP data is forced to larger values of and smaller values of
. Hence, we find an upper bound m_A \lsim 1.3 TeV. This in turn leads to
lower bounds on (assuming minimal
flavor violation) and on the dark matter spin independent detection cross
section \sigsip > 10^{-9} pb. Finally, we extend our previous analysis to
include WIMP signals in indirect detection and find prospects for WIMP
detection generally much less promising than in direct WIMP searches.Comment: 24 page
High-energy Neutrino Astronomy: The Cosmic Ray Connection
This is a review of neutrino astronomy anchored to the observational fact
that Nature accelerates protons and photons to energies in excess of
and eV, respectively.
Although the discovery of cosmic rays dates back close to a century, we do
not know how and where they are accelerated. Basic elementary-particle physics
dictates a universal upper limit on their energy of eV, the
so-called Greisen-Kuzmin-Zatsepin cutoff; however, particles in excess of this
energy have been observed by all experiments, adding one more puzzle to the
cosmic ray mystery. Mystery is fertile ground for progress: we will review the
facts as well as the speculations about the sources including gamma ray bursts,
blazars and top-down scenarios.
The important conclusion is that, independently of the specific blueprint of
the source, it takes a kilometer-scale neutrino observatory to detect the
neutrino beam associated with the highest energy cosmic rays and gamma rays. We
also briefly review the ongoing efforts to commission such instrumentation.Comment: 83 pages, 18 figures, submitted to Reports on Progress in Physic
Ubiquitous molecular substrates for associative learning and activity-dependent neuronal facilitation.
Recent evidence suggests that many of the molecular cascades and substrates that contribute to learning-related forms of neuronal plasticity may be conserved across ostensibly disparate model systems. Notably, the facilitation of neuronal excitability and synaptic transmission that contribute to associative learning in Aplysia and Hermissenda, as well as associative LTP in hippocampal CA1 cells, all require (or are enhanced by) the convergence of a transient elevation in intracellular Ca2+ with transmitter binding to metabotropic cell-surface receptors. This temporal convergence of Ca2+ and G-protein-stimulated second-messenger cascades synergistically stimulates several classes of serine/threonine protein kinases, which in turn modulate receptor function or cell excitability through the phosphorylation of ion channels. We present a summary of the biophysical and molecular constituents of neuronal and synaptic facilitation in each of these three model systems. Although specific components of the underlying molecular cascades differ across these three systems, fundamental aspects of these cascades are widely conserved, leading to the conclusion that the conceptual semblance of these superficially disparate systems is far greater than is generally acknowledged. We suggest that the elucidation of mechanistic similarities between different systems will ultimately fulfill the goal of the model systems approach, that is, the description of critical and ubiquitous features of neuronal and synaptic events that contribute to memory induction