Flavor SU(3) analysis of charmless B->PP decays

We perform a global fits to charmless $B \to PP$ decays which independently constrain the $(\bar\rho,\bar\eta)$ vertex of the unitarity triangle. The fitted amplitudes and phase are used to predict the branching ratios and CP asymmetries of all decay modes, including those of the $B_s$ system. Different schemes of SU(3) breaking in decay amplitude sizes are analyzed. The possibility of having a new physics contribution to $K \pi$ decays is also discussed.Comment: 3 pages, 2 figs. Talk given at EPS-HEP07 To appear in the proceedings, Reference adde

Signatures of Non-commutative QED at Photon Colliders

In this paper we study non-commutative (NC) QED signatures at photon colliders through pair production of charged leptons $(\ell^+ \ell^-)$ and charged scalars $(H^+ H^-)$. The NC corrections for the fermion pair production can be easily obtained since NC QED with fermions has been extensively studied in the literature. NC QED with scalars is less studied. To obtain the cross section for $H^+H^-$ productions, we first investigate the structure of NC QED with scalars, and then study the corrections due to the NC geometry to the ordinary QED cross sections. Finally by folding in the photon spectra for a $\gamma \gamma$ collider with laser back-scattered photons from the $e^+ e^-$ machine, we obtain 95% CL lower bound on the NC scale using the above two processes. We find that, with $\sqrt{s} = 0.5, 1.0$, and $1.5$ TeV and integrated luminosity $L = 500(fb^{-1})$, the NC scale up to 0.7, 1.2, and 1.6 TeV can be probed, respectively, while, for monochromatic photon beams, these numbers become 1.1, 1.7, 2.6 TeV, respectively.Comment: 16 pages, 7 figure

|V_ub| and |V_cb|, Charm Counting and Lifetime Differences in Inclusive Bottom Hadron Decays

Inclusive bottom hadron decays are analyzed based on the heavy quark effective field theory (HQEFT). Special attentions in this paper are paid to the b\to u transitions and nonspectator effects. As a consequence, the CKM quark mixing matrix elements |V_ub| and |V_cb| are reliably extracted from the inclusive semileptonic decays B\to X_u e \nu and B\to X_c e \nu. Various observables, such as the semileptonic branch ratio B_SL, the lifetime differences among B^-, B^0, B_s and \Lambda_b hadrons, the charm counting n_c, are predicted and found to be consistent with the present experimental data.Comment: 20 pages, Revtex, 4 figures and 2 table

Inclusive Decays of Bottom Hadrons in New Formulation of Heavy Quark Effective Field Theory

We apply the new formulation of heavy quark effective field theory (HQEFT) to the inclusive decays of bottom hadrons. The long-term ambiguity of using heavy quark mass or heavy hadron mass for inclusive decays is clarified within the framework of the new formulation of HQEFT. The $1/m_b$ order corrections are absent and contributions from $1/m_b^2$ terms are calculated in detail. This enables us to reliably extract the important CKM matrix element $|V_{cb}|$ from the inclusive semileptonic decay rates. The resulting lifetime ratios $\tau(B^0_s)/\tau(B^0)$ and $\tau(\Lambda_b)/\tau(B^0)$ are found to well agree with the experimental data. We also calculate in detail the inclusive semileptonic branching ratios and the ratios of the $\tau$ and $\beta$ decay rates as well as the charm countings in the $B^0$, $B^0_s$ and $\Lambda_b$ systems. For $B^0$ decays, all the observables are found to be consistent with the experimental data. More precise data for the $B^0$ decays and further experimental measurements for the $B^0_s$ and $\Lambda_b$ systems will be very useful for testing the framework of new formulation of HQEFT at the level of higher order corrections.Comment: 20 pages, RevTex, 8 figures, 3 tables, revised version with `dressed heavy quark' being addressed, to be published in Int. J. Mod. Phys.

All-optical switching in lithium niobate directional couplers with cascaded nonlinearity

We report on intensity-dependent switching in lithium niobate directional couplers. Large nonlinear phase shifts that are due to cascading detune the coupling between the coupler branches, which makes all-optical switching possible. Depending on the input intensity, the output could be switched between the cross and the bar coupler branches with a switching ratio of 1:5 and a throughput of 80%

Tailoring a two-dimensional electron gas at the LaAlO3/SrTiO3 (001) interface by epitaxial strain

Recently a metallic state was discovered at the interface between insulating oxides, most notably LaAlO3 and SrTiO3. Properties of this two-dimensional electron gas (2DEG) have attracted significant interest due to its potential applications in nanoelectronics. Control over this carrier density and mobility of the 2DEG is essential for applications of these novel systems, and may be achieved by epitaxial strain. However, despite the rich nature of strain effects on oxide materials properties, such as ferroelectricity, magnetism, and superconductivity, the relationship between the strain and electrical properties of the 2DEG at the LaAlO3/SrTiO3 heterointerface remains largely unexplored. Here, we use different lattice constant single crystal substrates to produce LaAlO3/SrTiO3 interfaces with controlled levels of biaxial epitaxial strain. We have found that tensile strained SrTiO3 destroys the conducting 2DEG, while compressively strained SrTiO3 retains the 2DEG, but with a carrier concentration reduced in comparison to the unstrained LaAlO3/SrTiO3 interface. We have also found that the critical LaAlO3 overlayer thickness for 2DEG formation increases with SrTiO3 compressive strain. Our first-principles calculations suggest that a strain-induced electric polarization in the SrTiO3 layer is responsible for this behavior. It is directed away from the interface and hence creates a negative polarization charge opposing that of the polar LaAlO3 layer. This both increases the critical thickness of the LaAlO3 layer, and reduces carrier concentration above the critical thickness, in agreement with our experimental results. Our findings suggest that epitaxial strain can be used to tailor 2DEGs properties of the LaAlO3/SrTiO3 heterointerface

Puzzles in BB physics

I discuss some puzzles observed in exclusive $B$ meson decays, concentrating on the large difference between the direct CP asymmetries in the $B^0\to \pi^\mp K^\pm$ and $B^\pm\to \pi^0 K^\pm$ modes, the large $B^0\to\pi^0\pi^0$ branching ratio, and the large deviation of the mixing-induced CP asymmetries in the $b\to sq\bar q$ penguins from those in the $b\to c\bar c s$ trees.Comment: 6 pages, 1 figure, talk presented at the 9th Workshop on High Energy Physics Phenomenology, Bhubaneswar, Orissa, India, Jan. 3-14, 2006; reference adde

All-Optical Integrated Mach-Zehnder Switching Due To Cascaded Nonlinearities

We demonstrate all-optical switching using the cascaded second order nonlinearity in a fully integrated, asymmetric Mach Zehnder interferometer implemented in lithium niobate channel waveguides. We obtained an 8:1 switching ratio