370 research outputs found

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### Multidimensional mSUGRA likelihood maps

We calculate the likelihood map in the full 7 dimensional parameter space of
the minimal supersymmetric standard model (MSSM) assuming universal boundary
conditions on the supersymmetry breaking terms. Simultaneous variations of m_0,
A_0, M_{1/2}, tan beta, m_t, m_b and alpha_s(M_Z) are applied using a Markov
chain Monte Carlo algorithm. We use measurements of b -> s gamma, (g-2)_mu and
Omega_{DM} h^2 in order to constrain the model. We present likelihood
distributions for some of the sparticle masses, for the branching ratio of
B_s^0 -> mu^+ mu^- and for m_{stau}-m_{chi_1^0}. An upper limit of 2.10^{-8} on
this branching ratio might be achieved at the Tevatron, and would rule out 29%
of the currently allowed likelihood. If one allows for non thermal-neutralino
components of dark matter, this fraction becomes 35%. The mass ordering allows
the important cascade decay squark_L -> chi_2^0 -> slepton_R -> chi_1^0 with a
likelihood of 24+/-4%. The stop coannihilation region is highly disfavoured,
whereas the light Higgs region is marginally disfavoured

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### Sampling using a 'bank' of clues

An easy-to-implement form of the Metropolis Algorithm is described which,
unlike most standard techniques, is well suited to sampling from multi-modal
distributions on spaces with moderate numbers of dimensions (order ten) in
environments typical of investigations into current constraints on
Beyond-the-Standard-Model physics. The sampling technique makes use of
pre-existing information (which can safely be of low or uncertain quality)
relating to the distribution from which it is desired to sample. This
information should come in the form of a ``bank'' or ``cache'' of space points
of which at least some may be expected to be near regions of interest in the
desired distribution. In practical circumstances such ``banks of clues'' are
easy to assemble from earlier work, aborted runs, discarded burn-in samples
from failed sampling attempts, or from prior scouting investigations. The
technique equilibrates between disconnected parts of the distribution without
user input. The algorithm is not lead astray by ``bad'' clues, but there is no
free lunch: performance gains will only be seen where clues are helpful

### $U(1)_{B_3-L_2}$ Explanation of the Neutral Current $B-$Anomalies

We investigate a speculative short-distance force, proposed to explain
discrepancies observed between measurements of certain neutral current decays
of $B$ hadrons and their Standard Model predictions. The force derives from a
spontaneously broken, gauged $U(1)_{B_3-L_2}$ 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 $U(1)_{B_3-L_2}$ and a Standard Model singlet complex scalar
which breaks $U(1)_{B_3-L_2}$, a `flavon'. This simple model, via interactions
involving a TeV scale force-carrying $Z^\prime$ vector boson, can successfully
explain the neutral current $B-$anomalies whilst accommodating other empirical
constraints. In an ansatz for fermion mixing, a combination of up-to-date
$B-$anomaly fits, LHC direct $Z^\prime$ search limits and other bounds rule out
the domain 0.15 TeV$< M_{Z^\prime} <$ 1.9 TeV at the 95$\%$ confidence level.
For more massive $Z^\prime$s, the model possesses a {\em flavonstrahlung}\
signal, where $pp$ collisions produce a $Z^\prime$ and a flavon, which
subsequently decays into two Higgs bosons

### The impact of the ATLAS zero-lepton, jets and missing momentum search on a CMSSM fit

Recent ATLAS data significantly extend the exclusion limits for
supersymmetric particles. We examine the impact of such data on global fits of
the constrained minimal supersymmetric standard model (CMSSM) to indirect and
cosmological data. We calculate the likelihood map of the ATLAS search, taking
into account systematic errors on the signal and on the background. We validate
our calculation against the ATLAS determinaton of 95% confidence level
exclusion contours. A previous CMSSM global fit is then re-weighted by the
likelihood map, which takes a bite at the high probability density region of
the global fit, pushing scalar and gaugino masses up.Comment: 16 pages, 7 figures. v2 has bigger figures and fixed typos. v3 has
clarified explanation of our handling of signal systematic

### Uncertainties in the lightest CP even Higgs boson mass prediction in the minimal supersymmetric standard model: fixed order versus effective field theory prediction

We quantify and examine the uncertainties in predictions of the lightest $CP$
even Higgs boson pole mass $M_h$ in the Minimal Supersymmetric Standard Model
(MSSM), utilising current spectrum generators and including some three-loop
corrections. There are two broadly different approximations being used:
effective field theory (EFT) where an effective Standard Model (SM) is used
below a supersymmetric mass scale, and a fixed order calculation, where the
MSSM is matched to QCD$\times$QED at the electroweak scale. The uncertainties
on the $M_h$ prediction in each approach are broken down into logarithmic and
finite pieces. The inferred values of the stop mass parameters are sensitively
dependent upon the precision of the prediction for $M_h$. The fixed order
calculation appears to be more accurate below a supersymmetry (SUSY) mass scale
of $M_S \approx 1.2$ TeV, whereas above this scale, the EFT calculation is more
accurate. We also revisit the range of the lightest stop mass across fine-tuned
parameter space that has an appropriate stable vacuum and is compatible with
the lightest $CP$ even Higgs boson $h$ being identified with the one discovered
at the ATLAS and CMS experiments in 2012; we achieve a maximum value of $\sim
10^{11}$ GeV

### The calculation of sparticle and Higgs decays in the minimal and next-to-minimal supersymmetric standard models: SOFTSUSY4.0

We describe a major extension of the SOFTSUSY spectrum calculator to include
the calculation of the decays, branching ratios and lifetimes of sparticles
into lighter sparticles, covering the next-to-minimal supersymmetric standard
model (NMSSM) as well as the minimal supersymmetric standard model (MSSM). This
document acts as a manual for the new version of SOFTSUSY, which includes the
calculation of sparticle decays. We present a comprehensive collection of
explicit expressions used by the program for the various partial widths of the
different decay modes in the appendix

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### Measuring smuon-selectron mass splitting at the CERN LHC and patterns of supersymmetry breaking

With sufficient data, Large Hadron Collider (LHC) experiments can constrain
the selectron-smuon mass splitting through differences in the di-electron and
di-muon edges from supersymmetry (SUSY) cascade decays. We study the
sensitivity of the LHC to this mass splitting, which within mSUGRA may be
constrained down to O(10^{-4}) for 30 fb^{-1} of integrated luminosity. Over
substantial regions of SUSY breaking parameter space the fractional edge
splitting can be significantly enhanced over the fractional mass splitting.
Within models where the selectron and smuon are constrained to be universal at
a high scale, edge splittings up to a few percent may be induced by
renormalisation group effects and may be significantly discriminated from zero.
The edge splitting provides important information about high-scale SUSY
breaking terms and should be included in any fit of LHC data to high-scale
models

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### Erratum to: U (1 ) B 3 - L 2 explanation of the neutral current B- anomalies (The European Physical Journal C, (2021), 81, 1, (56), 10.1140/epjc/s10052-021-08855-w)

A Correction to this paper has been published https://doi.org/10.1140/epjc/s10052-021-08855-w</jats:p

### ATLAS diboson excess could be an R -parity violating dismuon excess

We propose a new possible explanation of the ATLAS di-boson excess: that it
is due to heavy resonant slepton production, followed by decay into di-smuons.
The smuon has a mass not too far from the W and Z masses, and so it is easily
confused with W or Z bosons after its subsequent decay into di-jets, through a
supersymmetry violating and R-parity violating interaction. Such a scenario is
not currently excluded by other constraints and remains to be definitively
tested in Run II of the LHC. Such light smuons can easily simultaneously
explain the discrepancy between the measurement of the anomalous magnetic
moment of the muon and the Standard Model prediction.This work of B.C.A. has been partially supported by STFC grant ST/L000385/1. The work of P.S.B.D. is supported in part by a TUM University Foundation Fellowship and the DFG cluster of excellence “Origin and Structure of the Universe”.This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevD.93.03501

### The dark side of mSUGRA

We study the mu<0 branch of the minimal supergravity ansatz of the minimal
supersymmetric standard model. The extent to which mu<0 is disfavoured compared
to mu>0 in global fits is calculated with Markov Chain Monte Carlo methods and
bridge sampling. The fits include state-of-the-art two-loop MSSM contributions
to the electroweak observables M_W and sin^2 theta_w^l, as well as the
anomalous magnetic moment of the muon (g-2)_mu, the relic density of dark
matter and other relevant indirect observables. mu<0 is only marginally
disfavoured in global fits and should be considered in mSUGRA analyses. We
estimate that the ratio of probabilities is P(mu0)=0.07-0.16

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