Particle theory

Abstract:

We study the $\Delta I = 1/2$ rule for kaon decays and the $B_K$ parameter for $K^0 - {\bar K}^0$ mixing in a dual 5-dimensional holographic QCD model. We perform, in the chiral limit, computations of the relevant four-point current-current correlators, which depend upon self-interactions among the 5D bulk fields. Spontaneous chiral symmetry breaking ($\chi$SB) is realized through boundary conditions on the bulk fields. Numerical results are analyzed in comparison with QCD, chiral perturbation theory ($\chi$PT) and data, finding reasonable agreement with the experimental values of the $g_8$ and $g_{27}$ parameters describing the $\Delta I =1/2,3/2$ decay channels.

Abstract:

We have shown earlier that, contrary to popular belief, Einstein--de Sitter (E--deS) models can still fit the {\sl WMAP} data on the cosmic microwave background provided one adopts a low Hubble constant and relaxes the usual assumption that the primordial density perturbation is scale-free. The recent {\sl SDSS} measurement of the large-scale correlation function of luminous red galaxies at $z \sim 0.35$ has however provided a new constraint by detecting a `baryon acoustic peak'. Our best-fit E--deS models do possess a baryonic feature at a similar physical scale as the best-fit $\Lambda$CDM concordance model, but do not fit the new observations as well as the latter. In particular the shape of the correlation function in the range $\sim 10-100 h^{-1}$ Mpc cannot be reproduced properly without violating the CMB angular power spectrum in the multipole range $l \sim 100-1000$. Thus, the combination of the CMB fluctuations and the shape of the correlation function up to $\sim 100 h^{-1}$Mpc, if confirmed, does seem to require dark energy for a homogeneous cosmological model based on (adiabatic) inflationary perturbations.