327 research outputs found
Constrained MSSM favoring new territories: The impact of new LHC limits and a 125 GeV Higgs boson
We present an updated and extended global analysis of the Constrained MSSM
(CMSSM) taking into account new limits on supersymmetry from ~5/fb data sets at
the LHC. In particular, in the case of the razor limit obtained by the CMS
Collaboration we simulate detector efficiency for the experimental analysis and
derive an approximate but accurate likelihood function. We discuss the impact
on the global fit of a possible Higgs boson with mass near 125 GeV, as implied
by recent data, and of a new improved limit on BR(B_s->\mu\mu). We identify
high posterior probability regions of the CMSSM parameters as the
stau-coannihilation and the A-funnel region, with the importance of the latter
now being much larger due to the combined effect of the above three LHC results
and of dark matter relic density. We also find that the focus point region is
now disfavored. Ensuing implications for superpartner masses favor even larger
values than before, and even lower ranges for dark matter spin-independent
cross section, \sigma^{SI}_p<10^{-9} pb. We also find that relatively minor
variations in applying experimental constraints can induce a large shift in the
location of the best-fit point. This puts into question the robustness of
applying the usual chisquare approach to the CMSSM. We discuss the
goodness-of-fit and find that, while it is difficult to calculate a p-value,
the g-2 constraint makes, nevertheless, the overall fit of the CMSSM poor. We
consider a scan without this constraint, and we allow \mu\ to be either
positive or negative. We find that the global fit improves enormously for both
signs of \mu, with a slight preference for \mu<0 caused by a better fit to
BR(b->s\gamma) and BR(B_s->\mu\mu).Comment: 24 pages, 17 figures. PRD-approved version; Higgs bounds case removed
as obsolete in light of the Higgs discover
Bayesian Implications of Current LHC and XENON100 Search Limits for the Constrained MSSM
The CMS Collaboration has released the results of its search for
supersymmetry, by applying an alphaT method to 1.1/fb of data at 7 TeV. The
null result excludes (at 95% CL) a low-mass region of the Constrained MSSM's
parameter space that was previously favored by other experiments. Additionally,
the negative result of the XENON100 dark matter search has excluded (at 90% CL)
values of the spin-independent scattering cross sections sigma^SI_p as low as
10^-8 pb. We incorporate these improved experimental constraints into a global
Bayesian fit of the Constrained MSSM by constructing approximate likelihood
functions. In the case of the alphaT limit, we simulate detector efficiency for
the CMS alphaT 1.1/fb and validate our method against the official 95% CL
contour. We identify the 68% and 95% credible posterior regions of the CMSSM
parameters, and also find the best-fit point. We find that the credible regions
change considerably once a likelihood from alphaT is included, in particular
the narrow light Higgs resonance region becomes excluded, but the focus
point/horizontal branch region remains allowed at the 1sigma level. Adding the
limit from XENON100 has a weaker additional effect, in part due to large
uncertainties in evaluating sigma^SI_p, which we include in a conservative way,
although we find that it reduces the posterior probability of the focus point
region to the 2sigma level. The new regions of high posterior favor squarks
lighter than the gluino and all but one Higgs bosons heavy. The dark matter
neutralino mass is found in the range 250 GeV <~ m_Chi1 <~ 343 GeV (at 1sigma)
while, as the result of improved limits from the LHC, the favored range of
sigma^SI_p is pushed down to values below 10^{-9} pb. We highlight tension
between (g-2)_mu and BR(b->sg), which is exacerbated by including the alphaT
limit; each constraint favors a different region of the CMSSM's mass
parameters.Comment: Accepted by PRD. Added discussions on prior dependence and the
p-value. Main conclusions unchanged. 21 pages, 12 figure
Recommended from our members
Public goods and private interests: Understanding non-residential demand for green power
This article presents the results of the first large-scale mail survey of non-residential green power customers in the United States. The survey explored the motivations, attitudes, and experiences of 464 business, non-profit, and public-sector customers that have voluntarily opted to purchase - and frequently pay a premium for - renewable electricity. Results of this study should be of value to marketers interested in targeting these customer segments, to policy makers interested in fostering and understanding non-residential demand for green power, and to academics pondering the motivations for firms to engage in such voluntary environmental initiatives
Optical properties of LaNiO3 films tuned from compressive to tensile strain
Materials with strong electronic correlations host remarkable -- and
technologically relevant -- phenomena such as magnetism, superconductivity and
metal-insulator transitions. Harnessing and controlling these effects is a
major challenge, on which key advances are being made through lattice and
strain engineering in thin films and heterostructures, leveraging the complex
interplay between electronic and structural degrees of freedom. Here we show
that the electronic structure of LaNiO3 can be tuned by means of lattice
engineering. We use different substrates to induce compressive and tensile
biaxial epitaxial strain in LaNiO3 thin films. Our measurements reveal
systematic changes of the optical spectrum as a function of strain and,
notably, an increase of the low-frequency free carrier weight as tensile strain
is applied. Using density functional theory (DFT) calculations, we show that
this apparently counter-intuitive effect is due to a change of orientation of
the oxygen octahedra.The calculations also reveal drastic changes of the
electronic structure under strain, associated with a Fermi surface Lifshitz
transition. We provide an online applet to explore these effects. The
experimental value of integrated spectral weight below 2 eV is significantly
(up to a factor of 3) smaller than the DFT results, indicating a transfer of
spectral weight from the infrared to energies above 2 eV. The suppression of
the free carrier weight and the transfer of spectral weight to high energies
together indicate a correlation-induced band narrowing and free carrier mass
enhancement due to electronic correlations. Our findings provide a promising
avenue for the tuning and control of quantum materials employing lattice
engineering.Comment: 12 pages, 11 figure
Implications of the 125 GeV Higgs boson for scalar dark matter and for the CMSSM phenomenology
We study phenomenological implications of the ATLAS and CMS hint of a GeV Higgs boson for the singlet, and singlet plus doublet non-supersymmetric
dark matter models, and for the phenomenology of the CMSSM. We show that in
scalar dark matter models the vacuum stability bound on Higgs boson mass is
lower than in the standard model and the 125 GeV Higgs boson is consistent with
the models being valid up the GUT or Planck scale. We perform a detailed study
of the full CMSSM parameter space keeping the Higgs boson mass fixed to GeV, and study in detail the freeze-out processes that imply the observed
amount of dark matter. After imposing all phenomenological constraints except
for the muon we show that the CMSSM parameter space is divided
into well separated regions with distinctive but in general heavy sparticle
mass spectra. Imposing the constraint introduces severe tension
between the high SUSY scale and the experimental measurements -- only the
slepton co-annihilation region survives with potentially testable sparticle
masses at the LHC. In the latter case the spin-independent DM-nucleon
scattering cross section is predicted to be below detectable limit at the
XENON100 but might be of measurable magnitude in the general case of light dark
matter with large bino-higgsino mixing and unobservably large scalar masses.Comment: 17 pages, 7 figures. v3: same as published versio
The impact of XENON100 and the LHC on Supersymmetric Dark Matter
The effect of 2010 and 2011 LHC data are discussed in connection to the
potential for the direct detection of supersymmetric dark matter. The impact of
the recent XENON100 results are contrasted to these predictions.Comment: 14 pages, 23 figures, To be published in the Proceedings of the 7th
DSU Conference, Beijing Chin
MFV Reductions of MSSM Parameter Space
The 100+ free parameters of the minimal supersymmetric standard model (MSSM)
make it computationally difficult to compare systematically with data,
motivating the study of specific parameter reductions such as the cMSSM and
pMSSM. Here we instead study the reductions of parameter space implied by using
minimal flavour violation (MFV) to organise the R-parity conserving MSSM, with
a view towards systematically building in constraints on flavour-violating
physics. Within this framework the space of parameters is reduced by expanding
soft supersymmetry-breaking terms in powers of the Cabibbo angle, leading to a
24-, 30- or 42-parameter framework (which we call MSSM-24, MSSM-30, and MSSM-42
respectively), depending on the order kept in the expansion. We provide a
Bayesian global fit to data of the MSSM-30 parameter set to show that this is
manageable with current tools. We compare the MFV reductions to the
19-parameter pMSSM choice and show that the pMSSM is not contained as a subset.
The MSSM-30 analysis favours a relatively lighter TeV-scale pseudoscalar Higgs
boson and with multi-TeV sparticles.Comment: 2nd version, minor comments and references added, accepted for
publication in JHE
Probing natural SUSY from stop pair production at the LHC
We consider the natural supersymmetry scenario in the framework of the
R-parity conserving minimal supersymmetric standard model (called natural MSSM)
and examine the observability of stop pair production at the LHC. We first scan
the parameters of this scenario under various experimental constraints,
including the SM-like Higgs boson mass, the indirect limits from precision
electroweak data and B-decays. Then in the allowed parameter space we study the
stop pair production at the LHC followed by the stop decay into a top quark
plus a lightest neutralino or into a bottom quark plus a chargino. From
detailed Monte Carlo simulations of the signals and backgrounds, we find the
two decay modes are complementary to each other in probing the stop pair
production, and the LHC with TeV and 100 luminosity is
capable of discovering the stop predicted in natural MSSM up to 450 GeV. If no
excess events were observed at the LHC, the 95% C.L. exclusion limits of the
stop masses can reach around 537 GeV.Comment: 19 pages, 10 figures, version accepted by JHE
- …