119288545
Constraints on the Brans-Dicke gravity theory with the Planck data
Based on the new cosmic CMB temperature data from the Planck satellite, the 9 year polarization data from the WMAP, the BAO distance ratio data from the SDSS and 6dF surveys, we place a new constraint on the Brans-Dicke theory. We adopt a parametrization $\zeta=\ln(1+1/\omega})$, where the general relativity (GR) limit corresponds to $\zeta = 0$. We find no evidence of deviation from general relativity. At 95% probability, $-0.00246 0$ (i.e. $\omega >0$) case, then the 95% probability interval is $\zeta 181.65$. We can also translate this result to a constraint on the variation of gravitational constant, and find the variation rate today as $\dot{G}=-1.42^{+2.48}_{-2.27} \times 10^{-13} $yr$^{-1} $ ($1\sigma$ error bar), the integrated change since the epoch of recombination is $\delta G/G = 0.0104^{+0.0186}_{-0.0067} $ ($1\sigma$ error bar). These limits on the variation of gravitational constant are comparable with the precision of solar system experiments.
118566169
Role of t-channel meson exchange in S-wave pi N and K N scattering
The low-energy S-wave pi N and K N scatterings are studied by the K-matrix approach within the meson exchange framework. The t-channel meson exchanges, especially rho and sigma exchanges, are found to play a very important role in these two processes. The t-channel rho exchange determines the isospin structure of the scattering amplitudes, it gives attractive force in the low isospin state but repulsive force in the high isospin state. The t-channel sigma exchange gives a very large contribution in these two processes, while it is negligible in meson-meson S-wave scatterings.
36290076
Embedding flipped SU(5) into SO(10)
We embed the flipped SU(5) models into the SO(10) models. After the SO(10) gauge symmetry is broken down to the flipped SU(5) x U(1)(X) gauge symmetry, we can split the five/one-plets and ten-plets in the spinor 16 and 16 Higgs fields via the stable sliding singlet mechanism. As in the flipped SU(5) models, these ten-plet Higgs fields can break the flipped SU(5) gauge symmetry down to the Standard Model gauge symmetry. The doublet-triplet splitting problem can be solved naturally by the missing partner mechanism, and the Higgsino-exchange mediated proton decay can be suppressed elegantly. Moreover, we show that there exists one pair of the light Higgs doublets for the electroweak gauge symmetry breaking. Because there exist two pairs of additional vector-like particles with similar intermediate-scale masses, the SU(5) and U(1)(X) gauge couplings can be unified at the GUT scale which is reasonably (about one or two orders) higher than the SU(2)(L) x SU(3)(C) unification scale. Furthermore, we briefly discuss the simplest SO(10) model with flipped SU(5) embedding, and point out that it can not work without fine-tuning.
118041104
Correction to the Running of Gauge Couplings out of Extra Dimensional Gravity
We study the gravitational correction to the gauge couplings in the extra dimension model where the gravity propagates in the (4+n)-dimensional bulk. We show by explicit calculation in the background field method that the one-loop correction coming from graviton Kaluza-Klein states is nontrivial and tends to make the theory anti-asymptotically free. For the theory characterized with asymptotic freedom, the correction will induce a nontrivial UV-stable fixed point. This may lead to an interesting possibility that the non-abelian gauge coupling constants $g_2$ and $g_3$ in the SM and that of the gravity $g_{\kappa}$ unify at the fixed point in the limit of high energy scale.