Constraining heavy colored resonances from top-antitop quark events

Recent measurements of the top quark charge asymmetry at Tevatron disfavor the existence of flavor universal axigluons and colorons at 2 sigmas. In this letter we explore the possibility to reconcile the data with these models and use the charge asymmetry and the invariant mass distribution of top-antitop quark pair events to constrain the mass and couplings of massive color-octet gauge bosons decaying to top quarks.Comment: 4 pages, 4 figures. References added, final version to appear in Phys.Rev.

All-optical control of surface plasmons by second-harmonic generation

Light with light control of surface plasmon polaritons is theoretically demonstrated. A barely simple and compact source of these waves consists in a finite number of slits (evenly spaced) perforating a metal film. The system scatters electromagnetic fields in one side of the metal film when it is illuminated from the opposite side by a polarized light source. High intensity light sources moreover efficiently generate light at second harmonic and higher frequencies in the metal led by optical nonlinearities. It is shown how the mixing of fields scattered by the slits from a weak beam at $\lambda$ wavelength, with the second harmonic fields generated by a high intensity $2 \lambda$ beam, creates a destructive interference of surface plasmons in one of the two possible directions of emission from the slits, while these are enhanced along the opposite direction. The unidirectional launching of surface plasmons is due to the different properties of symmetry at $\lambda$ whether they are linearly or nonlinearly generated. It is envisaged a nanodevice which might allow sending digital information codified in the surface plasmon field or be used to build ultra-narrow bandwidth surface plasmon frequency combs.Comment: 5 pages, 3 figures, Supplemental Materia

Spin-charge coupling in quantum wires at zero magnetic field

We discuss an approximation for the dynamic charge response of nonlinear spin-1/2 Luttinger liquids in the limit of small momentum. Besides accounting for the broadening of the charge peak due to two-holon excitations, the nonlinearity of the dispersion gives rise to a two-spinon peak, which at zero temperature has an asymmetric line shape. At finite temperature the spin peak is broadened by diffusion. As an application, we discuss the density and temperature dependence of the Coulomb drag resistivity due to long-wavelength scattering between quantum wires.Comment: 16 pages, 5 figures. This is an extended version of "Coulomb drag from spin-charge coupling at zero magnetic field

Do Exchange Rate Regimes Matter For Inflation And Exchange Rate Dynamics? The Case Of Central America.

This paper makes an empirical contribution to the discussion on the optimal exchange rate regime. Using as astudy case the experience of the Central American countries, we compare the dynamics of the Real Exchange Rate (RER) and inflation persistence between dollarized economies and countries with some degree of exchange rate flexibility. Our results show that the two dollarized countries in the region, El Salvador and Panama, are quite different in terms of RER and inflation dynamics. While in El Salvador the RER spends more time away from the equilibrium level than the non-dollarized countries in the region, the opposite is true for Panama. We also find that inflation persistence in El Salvador is similar to that of the other countries, but smaller in Panama. This leads us to the conclusion that some degree of exchange rate flexibility helps countries to have a RER more aligned with its fundamentals. Nevertheless, a long-lived, highly credible dollarized economy, like Panama, can reduce inflation persistence to such an extent that RER misalignments are actually less frequent than in countries with more flexible exchange rate regimes.