Lepton flavor violating processes in unparticle physics

We study the virtual effects of unparticle physics in the lepton flavor violating processes $M^0\to l^+l'^-$ and $e^+e^-\to l^+l'^-$ scattering, where $M^0$ denotes the pseudoscalar mesons: $\pi^0,K_L, D_0,B_0,B_s^0$ and $l,l'$ denote two different lepton flavors. For the decay of $B^0\to l^+l'^-$, there is no constraint from the current experimental upper bounds on the vector unparticle coupling with leptons. The constraint on the coupling constant between scalar unparticle field and leptons is sensitive to the scaling dimension of the unparticle $d_{\cal U}$. For the scattering process $e^-e^+\to l^-l'^+$, there is only constraint from experiments on the vector unparticle couplings with leptons but no constraint on the scalar unparticle. We study the $\sqrt s$ dependence of the cross section $\frac{1}{\sigma} \frac{d\sigma}{d\sqrt s}$ of $e^+e^-\to l^-l'^+$ with different values of $d_{\cal U}$. If $d_{\cal U}=1.5$, the cross section is independent on the center mass energy. For $d_{\cal U}>1.5$, the cross section increases with $\sqrt s$.Comment: 8 pages, revtex4,with 2 figures, to appear in Phys. Rev.

Oscillation in power spectrum of primordial gravitational wave as a signature of higher-order stringy corrections

In low-energy effective string theory, $\alpha'$ corrections involve the coupling of the dilaton field to Gauss-Bonnet term. We assume that the dilaton potential is fine tuned so that the dilaton field may oscillate rapidly for a while around the minimum of its potential but the inflation background is not affected. By numerical method, we find that if the dilaton starts to oscillate at the time of about $\sim 60$ e-folds before the end of inflation, $\alpha^\prime$ correction may bring unusual oscillations to the inflationary gravitational wave spectrum, which might be measurably imprinted in the CMB B-mode polarization.Comment: 19 pages, 7 figures; published version in JHEP, many details supplemented, including 3 appendixes and 1 figure; references and comments added, presentation improve

Chirality oscillation of primordial gravitational waves during inflation

We show that if the gravitational Chern-Simons term couples to a massive scalar field ($m>H$), the primordial gravitational waves (GWs) will show itself the chirality oscillation, i.e., the amplitudes of the left- and right-handed GWs modes will convert into each other and oscillate in their propagations. This oscillation will eventually develop a permanent difference of the amplitudes of both modes, which leads to nearly opposite oscillating shapes in the power spectra of the left- and right-handed primordial GWs. We discuss its implication to the CMB B-mode polarization.Comment: 14 pages, 11 figures; published version in JHEP; one figure added; references and comments adde