* Astronomy

Blobrana · L

RE: Higgs Particles

Blobrana · L

Physicists find new particle, but is it the Higgs?

Physicists have maintained that they will not announce the discovery of the Higgs until the signal surpasses 5 sigma, meaning that it has just a 0.00003% chance of being wrong. The ATLAS and CMS experiments are each seeing signals between 4.5 and 5 sigma, just a whisker away from a solid discovery claim. The results are also consistent with an analysis from the mothballed Tevatron collider, which was presented today at Fermilab in Batavia, Illinois.
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Blobrana · L

US sees stronger hints of Higgs

Hints of the Higgs boson detected last year by a US "atom smasher" have become even stronger, scientists have said.
The signal is seen at the 2.9-sigma level of certainty, which means there is roughly a one in 1,000 chance that the result is attributable to some statistical quirk in the data.
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Blobrana · L

Title: Hints of Standard Model Higgs Boson at the LHC and Light Dark Matter Searches
Authors: Xiao-Gang He, Bo Ren, Jusak Tandean

The most recent results of searches at the LHC for the Higgs boson h have turned up possible hints of such a particle with mass m_h about 125 GeV consistent with standard model (SM) expectations. This has many potential implications for the SM and beyond. We consider some of them in the contexts of a simple Higgs-portal dark matter (DM) model, the SM plus a real gauge-singlet scalar field D as the DM candidate, and a couple of its variations. In the simplest model with one Higgs doublet and three or four generations of fermions, for D mass m_D < m_h/2 the invisible decay h -> DD tends to have a substantial branching ratio. If future LHC data confirm the preliminary Higgs indications, m_D will have to exceed m_h/2. To keep the DM lighter than m_h/2, one will need to extend the model and also satisfy constraints from DM direct searches. The latter can be accommodated if the model provides sizable isospin violation in the DM-nucleon interactions. We explore this in a two-Higgs-doublet model combined with the scalar field D. This model can offer a 125-GeV SM-like Higgs and a light DM candidate having isospin-violating interactions with nucleons at roughly the required level, albeit with some degree of fine-tuning.

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Blobrana · L

Title: Confluence of Constraints in Gauge Mediation: The 125 GeV Higgs Boson and Goldilocks Cosmology
Authors: Jonathan L. Feng, Ze'ev Surujon, Hai-Bo Yu

Recent indications of a 125 GeV Higgs boson are challenging for gauge-mediated supersymmetry breaking (GMSB), since radiative contributions to the Higgs boson mass are not enhanced by significant stop mixing. This challenge should not be considered in isolation, however, as GMSB also generically suffers from two other problems: unsuppressed electric dipole moments and the absence of an attractive dark matter candidate. We show that all of these problems may be simultaneously solved by considering heavy superpartners, without extra fields or modified cosmology. Multi-TeV sfermions suppress the EDMs and raise the Higgs mass, and the dark matter problem is solved by Goldilocks cosmology, in which TeV neutralinos decay to GeV gravitinos that are simultaneously light enough to solve the flavour problem and heavy enough to be all of dark matter. The implications for collider searches and direct and indirect dark matter detection are sobering, but EDMs are expected near their current bounds, and the resulting non-thermal gravitino dark matter is necessarily warm, with testable cosmological implications.

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Blobrana · L

Title: The 125 GeV Higgs in the NMSSM in light of LHC results and astrophysics constraints
Authors: Daniel Albornoz Vasquez, Genevieve Belanger, Celine Boehm, Jonathan Da Silva, Peter Richardson, Chris Wymant

Recent LHC data suggest an excess in the Higgs decay channels into gamma gamma, W W and Z Z at roughly 125 GeV. The current excess in the diphoton channel is twice that expected from a Standard Model Higgs; whilst this may well change with more statistics, it is interesting to consider the implications should the result persist. Here, we assess whether the NMSSM with a neutralino dark matter candidate could explain this excess when astrophysical constraints (e.g. no overproduction of gamma rays and radio emission in the galaxy, no anomalous excess in the dark matter direct detection experiments and no dark matter overabundance) are imposed on the neutralino. This enables us to disregard unphysical regions of the parameter space even though the Higgs signal is compatible with the observed excess. The result of our analysis is that there are configurations of the parameter space which can explain the signal strength reported by the ATLAS and CMS collaborations for a Higgs mass within the required range. Should the observed signal strength finally be compatible with Standard Model expectations, it would be difficult to distinguish between the discovery of Standard Model Higgs and a SM-like Higgs from the NMSSM, unless one performs dedicated searches of very light Higgs bosons and possibly investigate peculiar signatures of supersymmetric particles. We also propose a new jets + missing E_T signal for the case where the LSP is a singlino-like neutralino.

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Blobrana · L

Using different search techniques, Tevatron physicists see hints of Higgs boson sighting consistent with those from LHC

New measurements announced today by scientists from the CDF and DZero collaborations at the Department of Energy's Fermi National Accelerator Laboratory indicate that the elusive Higgs boson may nearly be cornered. After analysing the full data set from the Tevatron accelerator, which completed its last run in September 2011, the two independent experiments see hints of a Higgs boson.
Physicists from the CDF and DZero collaborations found excesses in their data that might be interpreted as coming from a Higgs boson with a mass in the region of 115 to 135 GeV. In this range, the new result has a probability of being due to a statistical fluctuation at level of significance known among scientists as 2.2 sigma. This new result also excludes the possibility of the Higgs having a mass in the range from 147 to 179 GeV.
Physicists claim evidence of a new particle only if the probability that the data could be due to a statistical fluctuation is less than 1 in 740, or three sigmas. A discovery is claimed only if that probability is less than 1 in 3.5 million, or five sigmas.