Compact extra-dimensions as solution to the strong CP problem

We show that the strong CP problem can, in principle, be solved dynamically by adding extra-dimensions with compact topology. To this aim we consider a toy model for QCD, which contains a vacuum angle and a strong CP like problem. We further consider a higher dimensional theory, which has a trivial vacuum structure and which reproduces the perturbative properties of the toy model in the low-energy limit. In the weak coupling regime, where our computations are valid, we show that the vacuum structure of the low-energy action is still trivial and the strong CP problem is solved. No axion-like particle occur in this setup and therefore it is not ruled out by astrophysical bounds.Comment: Discussion adde

HAPS Gateway Link in the 5850-7075 MHz and Coexistence with Fixed Satellite Service

Gateway link is essential to connect HAPS platform to terrestrial based networks. This crucial link is incorporated in HAPS fixed service spectrum allocation in considerably high frequencies, renders the link for more attenuations by atmospheric gases, and rain effects, especially when the regional climate is not favorable. However, under the agenda item 1.20 of World Radio Conference-2012 (WRC-12) new HAPS allocation in the 5850-7075 MHz band is proposed. Although, spectrum features are incomparably reliable, on the contrary, Fixed Satellite Service (FSS) uplink transmissions will have signal levels much higher than those in HAPS systems and have the potential for causing interference at the HAPS gateway receiver. In this article a key aspect of co-channel interference phenomena is investigated to facilitate optimum frequency sharing in the band in question. By proposing mitigation techniques and statistical method this generic prediction model enhances the capability of the HAPS spectrum sharing and provides flexibility in spectrum planning for different fixed services

First Order Semiclassical Thermal String in the AdS Spacetime

We formulate the finite temperature theory for the free thermal excitations of the bosonic string in the anti-de Sitter (AdS) spacetime in the Thermo Field Dynamics (TFD) approach. The spacetime metric is treated exactly while the string and the thermal reservoir are semiclassically quantized at the first order perturbation theory with respect to the dimensionless parameter \epsilon = \a ' H^{-2}. In the conformal $D=2+1$ black-hole AdS background the quantization is exact. The method can be extended to the arbitrary AdS spacetime only in the first order perturbation. This approximation is taken in the center of mass reference frame and it is justified by the fact that at the first order the string dynamics is determined only by the interaction between the {\em free} string oscillation modes and the {\em exact} background. The first order thermal string is obtained by thermalization of the $T = 0$ system carried on by the TFD Bogoliubov operator. We determine the free thermal string states and compute the local entropy and free energy in the center of mass reference frame.Comment: Minor typos corrected. Two references added. LATeX file, 19 page

Anomalous Soft Photons in Hadron Production

Anomalous soft photons in excess of what is expected from electromagnetic bremsstrahlung have been observed in association with the production of hadrons, mostly mesons, in high-energy (K+)p, (pi+)p, (pi-)p, pp, and (e+)(e-) collisions. We propose a model for the simultaneous production of anomalous soft photons and mesons in quantum field theory, in which the meson production arises from the oscillation of color charge densities of the quarks of the underlying vacuum in the flux tube. As a quark carries both a color charge and an electric charge, the oscillation of the color charge densities will be accompanied by the oscillation of electric charge densities, which will in turn lead to the simultaneous production of soft photons during the meson production process. How the production of these soft photons may explain the anomalous soft photon data will be discussed. Further experimental measurements to test the model will be proposed.Comment: 19 pages, 2 figures, to be published in Physical Review

TFD Approach to Bosonic Strings and DPD_{P}-branes

In this work we explain the construction of the thermal vacuum for the bosonic string, as well that of the thermal boundary state interpreted as a $D_{p}$-brane at finite temperature. In both case we calculate the respective entropy using the entropy operator of the Thermo Field Dynamics Theory. We show that the contribution of the thermal string entropy is explicitly present in the $D_{p}$-brane entropy. Furthermore, we show that the Thermo Field approach is suitable to introduce temperature in boundary states.Comment: 6 pages, revtex, typos are corrected. Prepared for the Second Londrina Winter School-Mathematical Methods in Physics, August 25-30, 2002, Londrina-Pr, Brazil. To appear in a special issue of IJMP

One-loop fermionic corrections to the instanton transition in two dimensional chiral Higgs model

The one-loop fermionic contribution to the probability of an instanton transition with fermion number violation is calculated in the chiral Abelian Higgs model in 1+1 dimensions, where the fermions have a Yukawa coupling to the scalar field. The dependence of the determinant on fermionic, scalar and vector mass is determined. We show in detail how to renormalize the fermionic determinant in partial wave analysis, which is convenient for computations.Comment: 36 pages, 5 figure

Structure and functional motifs of GCR1, the only plant protein with a GPCR fold?

Whether GPCRs exist in plants is a fundamental biological question. Interest in deorphanizing new G protein coupled receptors (GPCRs), arises because of their importance in signaling. Within plants, this is controversial as genome analysis has identified 56 putative GPCRs, including GCR1 which is reportedly a remote homologue to class A, B and E GPCRs. Of these, GCR2, is not a GPCR; more recently it has been proposed that none are, not even GCR1. We have addressed this disparity between genome analysis and biological evidence through a structural bioinformatics study, involving fold recognition methods, from which only GCR1 emerges as a strong candidate. To further probe GCR1, we have developed a novel helix alignment method, which has been benchmarked against the the class A – class B - class F GPCR alignments. In addition, we have presented a mutually consistent set of alignments of GCR1 homologues to class A, class B and class F GPCRs, and shown that GCR1 is closer to class A and /or class B GPCRs than class A, class B or class F GPCRs are to each other. To further probe GCR1, we have aligned transmembrane helix 3 of GCR1 to each of the 6 GPCR classes. Variability comparisons provide additional evidence that GCR1 homologues have the GPCR fold. From the alignments and a GCR1 comparative model we have identified motifs that are common to GCR1, class A, B and E GPCRs. We discuss the possibilities that emerge from this controversial evidence that GCR1 has a GPCR fol

PP-Wave Light-Cone Free String Field Theory at Finite Temperature

In this paper, a real-time formulation of light-cone pp-wave string field theory at finite temperature is presented. This is achieved by developing the thermo field dynamics (TFD) formalism in a second quantized string scenario. The equilibrirum thermodynamic quantities for a pp-wave ideal string gas are derived directly from expectation values on the second quantized string thermal vacuum. Also, we derive the real-time thermal pp-wave closed string propagator. In the flat space limit it is shown that this propagator can be written in terms of Theta functions, exactly as the zero temperature one. At the end, we show how supestrings interactions can be introduced, making this approach suitable to study the BMN dictionary at finite temperature.Comment: 27 pages, revtex

Generalized BFT Formalism of Electroweak Theory in the Unitary Gauge

We systematically embed the SU(2)$\times$U(1) Higgs model in the unitary gauge into a fully gauge-invariant theory by following the generalized BFT formalism. We also suggest a novel path to get a first-class Lagrangian directly from the original second-class one using the BFT fields.Comment: 14 pages, Latex, no figure