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Bristol physicists search for signs of supersymmetry

The first results from direct searches for new physics were announced today from CERN's energy-upgraded Large Hadron Collider (LHC). Among these results was a search for signs of a new theory called supersymmetry in which members of the University of Bristol particle physics group have played a leading role.
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Popular physics theory running out of hiding places

Researchers at the Large Hadron Collider have detected one of the rarest particle decays seen in Nature.
The finding deals a significant blow to the theory of physics known as supersymmetry.
Many researchers had hoped the LHC would have confirmed this by now.

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Title: Constraints on the Universe as a Numerical Simulation
Authors: Silas R. Beane, Zohreh Davoudi, Martin J. Savage

Observable consequences of the hypothesis that the observed universe is a numerical simulation performed on a cubic space-time lattice or grid are explored. The simulation scenario is first motivated by extrapolating current trends in computational resource requirements for lattice QCD into the future. Using the historical development of lattice gauge theory technology as a guide, we assume that our universe is an early numerical simulation with unimproved Wilson fermion discretisation and investigate potentially-observable consequences. Among the observables that are considered are the muon g-2 and the current differences between determinations of alpha, but the most stringent bound on the inverse lattice spacing of the universe, b^(-1) >~ 10^(11) GeV, is derived from the high-energy cut off of the cosmic ray spectrum. The numerical simulation scenario could reveal itself in the distributions of the highest energy cosmic rays exhibiting a degree of rotational symmetry breaking that reflects the structure of the underlying lattice.

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Title: Dark/Visible Parallel Universes and Big Bang Nucleosynthesis
Authors: C. A. Bertulani, T. Frederico, J. Fuqua, M. S. Hussein, O. Oliveira, W. de Paula

We develop a model for visible matter-dark matter interaction based on the exchange of a massive gray boson called herein the Mulato. Our model hinges on the assumption that all known particles in the visible matter have their counterparts in the dark matter. We postulate six families of particles five of which are dark. This leads to the unavoidable postulation of six parallel worlds, the visible one and five invisible worlds. A close study of big bang nucleosynthesis (BBN), baryon asymmetries, cosmic microwave background (CMB) bounds, galaxy dynamics, together with the Standard Model assumptions, help us to set a limit on the mass and width of the new gauge boson. Modification of the statistics underlying the kinetic energy distribution of particles during the BBN is also discussed. The changes in reaction rates during the BBN due to a departure from the Debye-Hueckel electron screening model is also investigated.

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Where is SUSY?

Recent information from the LHC experiments, the relatively low mass of the new boson and other data coming from experiments looking for dark matter worldwide are placing new constraints on the existence of supersymmetry (SUSY). However, there is a large community of scientists that still believes that SUSY particles are out there. Like lost keys at night, perhaps we have been looking for SUSY under the wrong lamp-posts...
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Title: Constraints on Supersymmetry from LHC data on SUSY searches and Higgs bosons combined with cosmology and direct dark matter searches
Authors: C. Beskidt (1), W. de Boer (1), D. I. Kazakov (2,3), F. Ratnikov (1,3) ((1) Karlsruhe Institute of Technology, Germany, (2) Bogoliubov Laboratory of Theoretical Physics, JINR, Dubna, Russia, (3) ITEP, Moscow, Russia)

The ATLAS and CMS experiments did not find evidence for Supersymmetry using close to 5/fb of published LHC data at a centre-of-mass energy of 7 TeV. We combine these LHC data with data on B_s -> mu mu (LHCb experiment), the relic density (WMAP and other cosmological data) and upper limits on the dark matter scattering cross sections on nuclei (XENON100 data). The excluded regions in the constrained Minimal Supersymmetric SM (CMSSM) lead to gluinos excluded below 1270 GeV and dark matter candidates below 220 GeV for values of the scalar masses (m_0) below 1500 GeV. For large m_0 values the limits of the gluinos and the dark matter candidate are reduced to 970 GeV and 130 GeV, respectively. If a Higgs mass of 125 GeV is imposed on the fit, the preferred SUSY region is above this excluded region, but the size of the preferred region is strongly dependent on the assumed theoretical error.

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Cosmological moduli problem
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Title: Higgs, Moduli Problem, Baryogenesis and Large Volume Compactifications
Authors: Tetsutaro Higaki, Kohei Kamada, Fuminobu Takahashi

We consider the cosmological moduli problem in the context of high-scale supersymmetry breaking suggested by the recent discovery of the standard-model like Higgs boson. In order to solve the notorious moduli-induced gravitino problem, we focus on the LARGE volume scenario, in which the modulus decay into gravitinos can be kinematically forbidden. We then consider the Affleck-Dine mechanism with or without an enhanced coupling with the inflaton, taking account of possible Q-ball formation. We show that the baryon asymmetry of the present Universe can be generated by the Affleck-Dine mechanism in LARGE volume scenario, solving the moduli and gravitino problems.

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Title: Implications of the Higgs Boson Discovery for mSUGRA
Authors: Sujeet Akula, Pran Nath, Gregory Peim

A Bayesian analysis is carried out to identify the consistent regions of the mSUGRA parameter space, where the newly-discovered Higgs boson's mass is used as a constraint, along with other experimental constraints. It is found that m_{½} can lie in the sub TeV region, A_0/m_0 is mostly confined to a narrow strip with |A_0/m_0| \leq 1, while m_0 is typically a TeV or larger. Further, the Bayesian analysis is used to set 95% CL lower bounds on sparticle masses. Additionally, it is shown that the spin independent neutralino-proton cross section lies just beyond the reach of the current sensitivity but within the projected sensitivity of the SuperCDMS-1T and XENON-1T experiments, which explains why dark matter has thus far not been detected. The light sparticle spectrum relevant for the discovery of supersymmetry at the LHC are seen to be the gluino, the chargino and the stop with the gluino and the chargino as the most likely candidates.

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Lambda-SUSY model
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Title: Precision Unification in  lambda-SUSY with a 125 GeV Higgs
Authors: Edward Hardy, John March-Russell, James Unwin

It is challenging to explain the tentative 125 GeV Higgs signal in the Minimal Supersymmetric Standard Model (MSSM) without introducing excessive fine-tuning, and this motivates the study of non-minimal implementations of low energy supersymmetry (SUSY). A superpotential term \lambda SH_uH_d involving a Standard Model (SM) singlet state S leads to an additional source for the quartic interaction raising the mass of the lightest SM-like Higgs. However, in order to achieve m_h \approx 125 GeV with light stops and small stop mixing, it is necessary for \lambda \gtrsim 0.7 and consequently \lambda may become non-perturbative before the unification scale. Moreover, as argued by Barbieri, Hall, et al. low fine-tuning prefers the region \lambda~1-2, leading to new or non-perturbative physics involving S below the GUT scale ('\lambda SUSY' models). This raises the concern that precision gauge coupling unification, the prime piece of indirect experimental evidence for low energy SUSY, may be upset. Using the NSVZ exact \beta-function along with well motivated assumptions on the strong coupling dynamics we argue that this is not necessarily the case, but rather there exist classes of UV completions where the strong-coupling effects can naturally correct for the present ~3% discrepancy in the two-loop MSSM unification prediction for \alpha_s.

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Title: GUT and Supersymmetry at the LHC and in dark matter
Authors: Pran Nath

Conventional SO(10) models involve more than one scale for a complete breaking of the GUT symmetry requiring further assumptions on the VEVs of the Higgs fields that enter in the breaking to achieve viable models. Recent works where the breaking can be accomplished at one scale are discussed. There include models with just a pair of 144+\bar{144} of Higgs fields. Further extensions of this idea utilising 560+ \bar{560} of Higgs representations allow both the breaking at one scale, as well as accomplish a natural doublet-triplet splitting via the missing partner mechanism. More generally, we discuss the connection of high scale models to low energy physics in the context of supergravity grand unification. Here we discuss a natural solution to the little hierarchy problem and also discuss the implications of the LHC data for supersymmetry. It is shown that the LHC data implies that most of the parameter space of supergravity models consistent with the data lie on the Hyperbolic Branch of radiative breaking of the electroweak symmetry and more specifically on the Focal Surface of the Hyperbolic Branch. A discussion is also given of the implications of recent LHC data on the Higgs boson mass for the discovery of supersymmetry and for the search for dark matter.

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