217 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
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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
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
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
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
Efficiency and environmental impacts of electricity restructuring on coal-fired power plants
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
Path dependence in energy systems and economic development
Energy systems are subject to strong and long-lived path dependence, owing to technological, infrastructural, institutional and behavioural lock-ins. Yet, with the prospect of providing accessible cheap energy to stimulate economic development and reduce poverty, governments often invest in large engineering projects and subsidy policies. Here, I argue that while these may achieve their objectives, they risk locking their economies onto energy-intensive pathways. Thus, particularly when economies are industrializing, and their energy systems are being transformed and are not yet fully locked-in, policymakers should take care before directing their economies onto energy-intensive pathways that are likely to be detrimental to their long-run prosperity
Uncovering Natural Supersymmetry via the interplay between the LHC and direct Dark Matter detection
We have explored Natural Supersymmetry (NSUSY) scenarios with low values of the μ parameter which are characterised by higgsino-like Dark Matter (DM) and compressed spectra for the lightest MSSM particles, χ10, χ20 and χ1±. This scenario could be probed via monojet signatures, but as the signal-to-background ratio (S/B) is low we demonstrate that the 8 TeV LHC cannot obtain limits on the DM mass beyond those of LEP2. On the other hand, we have found, for the 13 TeV run of the LHC, that by optimising kinematical cuts we can bring the S/B ratio up to the 5(3)% level which would allow the exclusion of the DM mass up to 200(250) GeV respectively, significantly extending LEP2 limits. Moreover, we have found that LUX/XENON1T and LHC do play very complementary roles in exploring the parameter space of NSUSY, as the LHC has the capability to access regions where DM is quasi-degenerate with other higgsinos, which are challenging for direct detection experiments
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