We explore the cosmological implications of five modified gravity(MG) models by using the recent cosmological observational data,including the recently released SNLS3 type Ia supernovae sample,the cosmic microwave background anisotropy data from the Wilkinson Microwave Anisotropy Probe 7-yr observations,the baryon acoustic oscillation results from the Sloan Digital Sky Survey data release 7,and the latest Hubble constant measurement utilizing the Wide Field Camera 3 on the Hubble Space Telescope.The MG models considered include the Dvali-Gabadadze-Porrati(DGP) model,two f(R) models,and two f(T) models.We find that compared with the ΛCDM model,MG models can not lead to an appreciable reduction of the χ 2 min.The analysis of AIC and BIC shows that the simplest cosmological constant model(ΛCDM) is still the most preferred by the current data,and the DGP model is strongly disfavored.In addition,from the observational constraints,we also reconstruct the evolutions of the growth factor in these models.We find that the current available growth factor data are not enough to distinguish these MG models from the ΛCDM model.
We compare some popular dark energy models under the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation,the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey,the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations and the determination of H0 from the Hubble Space Telescope.Model comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the models.These statistics favor models that give a good fit with fewer parameters.Based on this analysis,we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current data.For other dynamical dark energy models,we find that some of them,such as the αdark energy,constant w,generalized Chaplygin gas,Chevalliear-Polarski-Linder parametrization,and holographic dark energy models,can provide good fits to the current data,and three of them,namely,the Ricci dark energy,agegraphic dark energy,and Dvali-Gabadadze-Porrati models,are clearly disfavored by the data.
LI Miao1,2,LI XiaoDong2,3 & ZHANG Xin1,4 1Kavli Institute for Theoretical Physics China,Chinese Academy of Sciences,Beijing 100190,China
We examine various direct and indirect constraints on the lepton-specific two-Higgs doublet model and discuss its phenomenology at colliders in the allowed parameter space.The constraints we consider come from the precision electroweak data,the direct search for Higgs boson,the muon anomalous magnetic moment,as well as some theoretical consistency requirements.We find that in the allowed parameter space the CP-odd Higgs boson A is rather light (m A < 30 GeV with 95% possibility),which is composed dominantly by the leptonic Higgs and decays dominantly into τ + τ;while the SM-like Higgs boson h (responsible largely for electroweak symmetry breaking) decays dominantly in the mode h → AA → 4τ with a large decay width,which will make the Higgs discovery more difficult at the LHC.Whereas,this scenario predicts rare Z decays Z → AAA and Z →τ + τA with their branching ratios ranging from 10-8 to 10-and 10-5 to 10-4 respectively,which may be accessible at the GigaZ option of the ILC.
CAO JunJie 1,HENG ZhaoXia 2,3 & WAN PeiHua 1 1 College of Physics & Information Engineering,Henan Normal University,Xinxiang 453007,China
We propose a new holographic program of gravity in which we introduce a surface stress tensor.Our proposal differs from Verlinde's in several aspects.First,we use an open or a closed screen.Second,the temperature is not necessary,but a surface energy density and pressure are introduced.The surface stress tensor is proportional to the extrinsic curvature.Third,the energy we use is Brown-York energy and the equipartition theorem is violated by a non-vanishing surface pressure.We discuss holographic thermodynamics of a gas of weak gravity and find a chemical potential,and then show that Verlinde's program does not lead to reasonable thermodynamics.The holographic entropy is similar to the Bekenstein entropy bound.
Extending the holographic program of our previous work,we derive f(R) gravity and the Maxwell equations from the holographic principle,using time-like holographic screens.We find that to derive the Einstein equations and f(R) gravity by a natural holographic approach,the quasi-static condition is necessary.We also find the surface stress tensor and the surface electric current,surface magnetic current on a holographic screen for f(R) gravity and Maxwell's theory,respectively.
Recently Background Imaging of Cosmic Extragalactic Polarization （B2） discovered the relic gravitational waves at 7.00- confi- dence level. However, the other cosmic microwave background （CMB） data, for example Planck data released in 2013 （P13）, prefer a much smaller amplitude of the primordial gravitational waves spectrum if a power-law spectrum of adiabatic scalar perturbations is assumed in the six-parameter ACDM cosmology. In this paper, we explore whether the wCDM model and the running spectral index can relax the tension between B2 and other CMB data. Specifically we found that a positive running of running of spectral index is preferred at 1.70- level from the combination of B2, P 13 and WMAP Polarization data.
Considering the constraints from collider experiments and dark matter detection, we investigate the SUSY effects in the Higgs production channels e＋e-, Zh at an e＋e- collider with a center-of-mass energy above 240 GeV and YY-- h - bb at a photon collider with a center-of-mass energy above 125 GeV. In the parameter space allowed by current experiments, we find that the SUSY corrections to e＋e- Zh can reach a few percent and the production rate of YY- h - bb can be enhanced by a factor of 1.2 over the SM prediction. We also calculate the exotic Higgs production e＋e- - Zhl in the next-to-minimal supersymmetric model （NMSSM） （h is the SM-like Higgs, hi is the CP-even Higgs bosons which can be much lighter than h）. We find that at a 250 GeV e＋e- collider the production rates of e＋e- -- Zhl can reach 60 fb.
Gravity/fluid correspondence acts as an important tool in investigating the strongly correlated fluids.We carefully investigate the holographic fluids at the finite cutoff surface by considering different boundary conditions in the scenario of gravity/fluid correspondence. We find that the sonic velocity of the boundary fluids at the finite cutoff surface is critical in clarifying the superficial similarity between the bulk viscosity and perturbation of the pressure for the holographic fluid, where we set a special boundary condition at the finite cutoff surface to explicitly express this superficial similarity. Moreover, we further take the sonic velocity into account to investigate a case with a more general boundary condition. In this more genaral case, although two parameters in the first order stress tensor of holographic fluid cannot be fixed, one can still extract the information about the transport coefficients by considering the sonic velocity seriously.
