106 research outputs found
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Explanation of the Neutral Current Anomalies
We investigate a speculative short-distance force, proposed to explain
discrepancies observed between measurements of certain neutral current decays
of hadrons and their Standard Model predictions. The force derives from a
spontaneously broken, gauged extension to the Standard Model,
where the extra quantum numbers of Standard Model fields are given by third
family baryon number minus second family lepton number. The only fields beyond
those of the Standard Model are three right-handed neutrinos, a gauge field
associated with and a Standard Model singlet complex scalar
which breaks , a `flavon'. This simple model, via interactions
involving a TeV scale force-carrying vector boson, can successfully
explain the neutral current anomalies whilst accommodating other empirical
constraints. In an ansatz for fermion mixing, a combination of up-to-date
anomaly fits, LHC direct search limits and other bounds rule out
the domain 0.15 TeV 1.9 TeV at the 95 confidence level.
For more massive s, the model possesses a {\em flavonstrahlung}\
signal, where collisions produce a and a flavon, which
subsequently decays into two Higgs bosons
Investigating Multiple Solutions in the Constrained Minimal Supersymmetric Standard Model
Recent work has shown that the Constrained Minimal Supersymmetric Standard
Model (CMSSM) can possess several distinct solutions for certain values of its
parameters. The extra solutions were not previously found by public
supersymmetric spectrum generators because fixed point iteration (the algorithm
used by the generators) is unstable in the neighbourhood of these solutions.
The existence of the additional solutions calls into question the robustness of
exclusion limits derived from collider experiments and cosmological
observations upon the CMSSM, because limits were only placed on one of the
solutions. Here, we map the CMSSM by exploring its multi-dimensional parameter
space using the shooting method, which is not subject to the stability issues
which can plague fixed point iteration. We are able to find multiple solutions
where in all previous literature only one was found. The multiple solutions are
of two distinct classes. One class, close to the border of bad electroweak
symmetry breaking, is disfavoured by LEP2 searches for neutralinos and
charginos. The other class has sparticles that are heavy enough to evade the
LEP2 bounds. Chargino masses may differ by up to around 10% between the
different solutions, whereas other sparticle masses differ at the sub-percent
level. The prediction for the dark matter relic density can vary by a hundred
percent or more between the different solutions, so analyses employing the dark
matter constraint are incomplete without their inclusion.Comment: 30 pages, 12 figures, 2 tables; v2: added discussion on speed of
shooting method, fixed typos, matches published versio
Non-Diagonal and Mixed Squark Production at Hadron Colliders
We calculate squared helicity amplitudes for non-diagonal and mixed squark
pair production at hadron colliders, taking into account not only loop-induced
QCD diagrams, but also previously unconsidered electroweak channels, which turn
out to be dominant. Mixing effects are included for both top and bottom
squarks. Numerical results are presented for several SUSY benchmark scenarios
at both the CERN LHC and the Fermilab Tevatron, including the possibilities of
light stops or sbottoms. The latter should be easily observed at the Tevatron
in associated production of stops and sbottoms for a large range of stop masses
and almost independently of the stop mixing angle. Asymmetry measurements for
light stops at the polarized BNL RHIC collider are also briefly discussed.Comment: 22 pages, 11 figure
Z boson decay to photon plus Kaluza-Klein graviton in large extra dimensions
In the large extra dimensional ADD scenario, Z bosons undergo a one-loop
decay into a photon and Kaluza-Klein towers of gravitons/gravi-scalars. We
calculate such a decay width, extending previous arguments about the general
form of the four-dimensional on-shell amplitude. The amplitudes calculated are
relevant to processes in other extra dimensional models where the Standard
Model fields are confined to a 4-brane.Comment: 47 pages, uses feynmp for diagrams. v2: typographical corrections for
letter-sized paper and to correct feynmf parsing error. v3: minor error in
polarisation averaging and reference corrected. v4: reflects changes for
published version; arithmetic error corrected and reference updated; section
on transversality conditions not present in published version retaine
Panglossian Prospects for Detecting Neutralino Dark Matter in Light of Natural Priors
In most global fits of the constrained minimal supersymmetric model (CMSSM)
to indirect data, the a priori likelihoods of any two points in tan beta are
treated as equal, and the more fundamental mu and B Higgs potential parameters
are fixed by potential minimization conditions. We find that, if instead a flat
("natural")prior measure on mu and B is placed, a strong preference exists for
the focus point region from fits to particle physics and cosmological data. In
particular, we find that the lightest neutralino is strongly favored to be a
mixed bino-higgsino (~10% higgsino). Such mixed neutralinos have large elastic
scattering cross sections with nuclei, leading to extremely promising prospects
for both underground direct detection experiments and neutrino telescopes. In
particular, the majority of the posterior probability distribution falls within
parameter space within an order of magnitude of current direct detection
constraints. Furthermore, neutralino annihilations in the sun are predicted to
generate thousands of neutrino induced muon events per years at IceCube. Thus,
assuming the framework of the CMSSM and using the natural prior measure, modulo
caveats regarding astrophysical uncertainties, we are likely to be living in a
world with good prospects for the direct and indirect detection of neutralino
dark matter.Comment: 25 pages, 9 figure
Neutrino masses and mixing angles in a supersymmetric SU(4) x SU(2) x SU(2)model
We consider the problem of neutrino masses and mixing angles in a supersymmetric model based on the gauge group SU(4)\otimesSU(2)_L\otimesSU(2)_R broken at the scale M_X\approx 10^{16} GeV. We extend a previous operator analysis of the charged lepton and quark masses and mixing angles in this model to include the neutrino sector, assuming a universal Majorana mass M for the right-handed neutrinos. The Dirac part of the neutrino matrix is then fixed and the physical neutrino masses and magnitudes of all of the elements of the leptonic mixing matrix are then predicted in terms of the single additional parameter M. The successful ansatze predict a tau neutrino mass in the relevant range for the dark matter problem and structure formation, muon and electron neutrinos consistent with the MSW solution to the solar neutrino problem, and tau-muon neutrino mixing at a level which should soon be observed by the CHORUS and NOMAD experiments
Theoretical uncertainties in sparticle mass predictions from computational tools
We estimate the current theoretical uncertainty in sparticle mass predictions
by comparing several state-of-the-art computations within the minimal
supersymmetric standard model (MSSM). We find that the theoretical uncertainty
is comparable to the expected statistical errors from the Large Hadron Collider
(LHC), and significantly larger than those expected from a future e+e- Linear
Collider (LC). We quantify the theoretical uncertainty on relevant sparticle
observables for both LHC and LC, and show that the value of the error is
significantly dependent upon the supersymmetry (SUSY) breaking parameters. We
also present the theoretical uncertainty induced in fundamental-scale SUSY
breaking parameters when they are fitted from LHC measurements. Two regions of
the SUSY parameter space where accurate predictions are particularly difficult
are examined in detail: the large tan(beta) and focus point regimes.Comment: 22 pages, 6 figures; comment added pointing out that 2-loop QCD
corrections to mt are incorrect in some of the programs investigated. We give
the correct formul
Fitting the Phenomenological MSSM
We perform a global Bayesian fit of the phenomenological minimal
supersymmetric standard model (pMSSM) to current indirect collider and dark
matter data. The pMSSM contains the most relevant 25 weak-scale MSSM
parameters, which are simultaneously fit using `nested sampling' Monte Carlo
techniques in more than 15 years of CPU time. We calculate the Bayesian
evidence for the pMSSM and constrain its parameters and observables in the
context of two widely different, but reasonable, priors to determine which
inferences are robust. We make inferences about sparticle masses, the sign of
the parameter, the amount of fine tuning, dark matter properties and the
prospects for direct dark matter detection without assuming a restrictive
high-scale supersymmetry breaking model. We find the inferred lightest CP-even
Higgs boson mass as an example of an approximately prior independent
observable. This analysis constitutes the first statistically convergent pMSSM
global fit to all current data.Comment: Added references, paragraph on fine-tunin
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
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