119233126
Higher derivative operators in the noncommutative Schwinger model
Abstract A study of the noncommutative Schwinger model is presented. It is shown that the Schwinger mass is not modified by the noncommutativity of spacetime till the first nontrivial order in the noncommutative parameter. Instead, a higher derivative kinetic term is dynamically generated by the lowest-order vacuum polarization diagrams. We argue that in the framework of the Seiberg–Witten map the feature of non-unitarity for a field theory with spacetime noncommutativity is characterized by the presence of higher derivative kinetic terms. The θ-expanded version of a unitary theory will not generate the lowest-order higher derivative quadratic terms.
117791238
What can we learn from a measurement of sin(2 beta + gamma)?
The constraints on the value of the Cabibbo-Kobayashi-Maskawa phase $\ensuremath{\gamma}$ that may be achieved by prospective measurements of $\mathrm{sin}2\ensuremath{\beta}$ and $\mathrm{sin}(2\ensuremath{\beta}+\ensuremath{\gamma})$ are discussed. Significant constraints require quite small errors, and may depend on assumptions about strong phases. The measurement of $\mathrm{sin}(2\ensuremath{\beta}+\ensuremath{\gamma})$ combined with other experiments could provide valuable limits on new physics in ${B}_{d}\ensuremath{-}$ mixing.
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.
8866225
AdS/QCD phenomenological models from a back-reacted geometry
We construct a fully back-reacted holographic dual of a four-dimensional field theory which exhibits chiral symmetry breaking. Two possible models are considered by studying the effects of a five-dimensional field, dual to the qq operator. One model has smooth geometry at all radii and the other dynamically generates a cutoff at finite radius. Both of these models satisfy Einstein's field equations. The second model has only three free parameters, as in QCD, and we show that this gives phenomenologically consistent results. We also discuss the possibility that in order to obtain linear confinement from a back-reacted model it may be necessary to consider the condensate of a dimension two operator.
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.
8450139
Electrodynamics modified by some dimension-five Lorentz-violating interactions: radiative corrections
We study radiative corrections to massless quantum electrodynamics modified by two dimension-five LV interactions $$\bar{\Psi } \gamma ^{\mu } b'^{\nu } F_{\mu \nu }\Psi $$Ψ¯γμb′νFμνΨ and $$\bar{\Psi }\gamma ^{\mu }b^{\nu } \tilde{F}_{\mu \nu } \Psi $$Ψ¯γμbνF~μνΨ in the framework of effective field theories. All divergent one-particle-irreducible Feynman diagrams are calculated at one-loop order and several related issues are discussed. It is found that massless quantum electrodynamics modified by the interaction $$\bar{\Psi } \gamma ^{\mu } b'^{\nu } F_{\mu \nu }\Psi $$Ψ¯γμb′νFμνΨ alone is one-loop renormalizable and the result can be understood on the grounds of symmetry. In this context the one-loop Lorentz-violating beta function is derived and the corresponding running coefficients are obtained.
119187103
Reducing the Tension Between the BICEP2 and the Planck Measurements: A Complete Exploration of the Parameter Space
A large inflationary tensor-to-scalar ratio r0.002 = 0.20 +0.07 0.05 is reported by the BICEP2 team based on their B-mode polarization detection, which is outside of the 95% confidence level of the Planck best fit model. We explore several possible ways to red uce the tension between the two by considering a model in whichαs, nt, ns and the neutrino parameters Neff andmν are set as free parameters. Using the Markov Chain Monte Carlo (MCMC) technique to survey the complete parameter space with and without the BICEP2 data, we find that the resulting constraints on r0.002 are consistent with each other and the apparent tension seems to be relaxed. Further detailed investigations on those fittin gs suggest that Neff probably plays the most important role in reducing the tension. We also find that the results obtained from fittin g without adopting the consistency relation do not deviate much from the consistency relation. With available Planck, WMAP, BICEP2 and BAO datasets all together, we obtain r0.002 = 0.14 +0.05 0.11 , nt = 0.35 +0.28 0.47 , ns = 0.98 +0.02 0.02 , andαs = 0.0086 +0.0148 0.0189 ; if the consistency relation is adopted, we get r0.002 = 0.22 +0.05 0.06 .
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.
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.