Results are presented from a search for the rare decays Bs(0)→μ+ μ- and B(0)→μ+ μ- in pp collisions at sqrt[s]=7 and 8 TeV, with data samples corresponding to integrated luminosities of 5 and 20  fb(-1), respectively, collected by the CMS experiment at the LHC. An unbinned maximum-likelihood fit to the dimuon invariant mass distribution gives a branching fraction B(Bs(0)→μ+ μ-)=(3.0(-0.9)(+1.0))×10(-9), where the uncertainty includes both statistical and systematic contributions. An excess of Bs(0)→μ+ μ- events with respect to background is observed with a significance of 4.3 standard deviations. For the decay B(0)→μ+ μ- an upper limit of B(B(0)→μ+ μ-)<1.1×10(-9) at the 95% confidence level is determined. Both results are in agreement with the expectations from the standard model.

We use the most recent Type Ia supernova data in order to study the dark energy-dark matter (XCDM) unification approach in the context of the generalized Chaplygin gas (GCG) model. Rather surprisingly, we find that data allow models with α > 1. We have studied how the GCG adjusts flat and non-flat models, and our results show that GCG is consistent with a flat case up to 68 per cent confidence level. Actually this holds even if one relaxes the flat prior assumption. We have also analysed what one should expect from a future experiment such as the Supernova/Acceleration Probe (SNAP). We find that there is a degeneracy between the GCG model and an XCDM model with a phantom-like dark energy component.

We investigate the constraints on the Cardassian model using the recent results from the Wilkinson microwave anisotropy probe for the locations of the peaks of the cosmic microwave background ͑CMB͒ anisotropy spectrum. We find that the model is consistent with the recent observational data for a certain range of the model parameter n and the cosmological parameters. We find that the Cardassian model is favored compared to the ⌳CDM model for a higher spectral index (n s Ϸ1) together with a lower value of the Hubble parameter h (hр0.71). But for smaller values of n s , both ⌳CDM and Cardassian models are equally favored. Also, irrespective of supernova constraints, CMB data alone predict the current acceleration of the Universe in this model. We have also studied the constraint on 8 , the rms density fluctuations at the 8h Ϫ1 Mpc scale.

In this work we have investigated the possibility of having a late time accelerated phase of the universe, suggested by recent supernova observation, in the context of Brans Dicke (BD) theory with potential having a time dependent mass squared term which has recently become negative and a matter field. We find that while a perfect fluid (pressureless and with pressure) cannot support this acceleration, a fluid with dissipative pressure can drive this late time acceleration for a simple power law expansion of the universe. We have also calculated some cosmological parameters in our model to match with observations. PACS Number(s): 04.20Jb, 98.80Hw

No abstract