119921028
Confinement in a Bethe-Salpeter model with logarithmic potential
We show that the covariant Bethe-Salpeter equation for two scalar quarks confined through a kernel of the form $K\ensuremath{\sim}{[{(p\ensuremath{-}{p}^{\ensuremath{'}})}^{2}]}^{\ensuremath{-}\frac{3}{2}}$ possesses a discrete spectrum: this kernel is a simple covariant generalization of the potential in configuration space proportional to $\mathrm{ln}r$. To investigate the spectrum, we adopt a new approximation scheme to convert the covariant Bethe-Salpeter equation into a three-dimensional one, the consistency of the scheme being checked by applying it to the Wick-Cutkosky equation for the covariant Coulomb problem and obtaining a Balmer-type formula. The spectrum as revealed by investigating the $S$-wave part of the resulting three-dimensional equation by semiclassical methods is essentially of the type obtained from the Schr\"odinger equation with a $\mathrm{ln}r$ potential; relativistic effects depress the energy levels.
118238640
HIGH-ORDER LOW-ENERGY THEOREMS FOR NUCLEON COMPTON SCATTERING.
The well-known zero- and first-order (in photon energy) low-energy theorems for nucleon Compton scattering have recently been derived by Abarbanel and Goldberger using only the physical helicity amplitudes for the process and exploiting their kinematical singularities and zeros. We use this approach to study higher-order terms in photon energy and find the result, not entirely new, that four of the six independent helicity amplitudes are determined in second order by the mass, charge, and magnetic moment of the nucleon. Therefore, these parameters together with two structure-dependent constants, which can be interpreted approximately as electric and magnetic polarizabilities, completely determine the Compton scattering to second order in energy. Similar simplifications occurring in the structure of higher-order terms in energy are also discussed. The kinematical singularity structure of helicity amplitudes is a manifestation of Lorentz invariance. We claim to have fully exploited the requirements of Lorentz invariance and therefore to have derived the complete set of low-energy theorems for this process.
122154027
Relativistic oscillator in a Bethe-Salpeter model: Nonexistence of discrete bound states
We investigate the solutions of the covariant Bethe-Salpeter equation for bound states of a scalar quark-antiquark system with an effective confining kernel which in coordinate four-space behaves as ${R}^{2}$. Using a suitable set of new variables we separate the equation into one-dimensional equations and study the eigenvalue problem. We find that the covariant bound-state Bethe-Salpeter equation with the above kernel possesses only a continuous spectrum.
121960660
Neutral-current cross sections for double-pion production by neutrinos
We have derived expressions for the differential cross sections for two-pion production by the neutral current in a neutrino-induced hadron reaction. We assume a general V, A form of the neutral current with arbitrary admixture of isotopic scalar and vector parts and utilize the algebra of currents and the PCAC (partial conservation of the axial-vector current) hypothesis to obtain the amplitude for ..nu.. + N ..-->.. ..nu.. + N + ..pi.. + ..pi... Two different cases have been studied: (i) Both the outgoing pions are at threshold. (ii) They are produced via the formation of N*. The results are useful to examine the structure of the neutral current.
125314068
Supersymmetric effects in B(s) ---> l+ l- gamma decays
10367884
Comment on "New interaction for the enhancement of the Delta I=1/2 amplitude in weak decays"
118378176
Brane inflation in background supergravity
We propose a model of inflation in the framework of brane cosmology driven by background supergravity. Starting from bulk supergravity we construct the inflaton potential on the brane and employ it to investigate for the consequences to inflationary paradigm. To this end, we derive the expressions for the important parameters in brane inflation, which are somewhat different from their counterparts in standard cosmology, using the one loop radiative corrected potential. We further estimate the observable parameters and find them to fit well with recent observational data by confronting with WMAP7 using CAMB. We also analyze the typical energy scale of brane inflation with our model, which resonates well with present estimates from cosmology and standard model of particle physics.
119307074
DBI Galileon inflation in background SUGRA
Abstract We introduce a model of potential driven DBI Galileon inflation in background N = 1 , D = 4 SUGRA. Starting from D4– D 4 ¯ brane–antibrane in the bulk N = 2 , D = 5 SUGRA including quadratic Gauss–Bonnet corrections, we derive an effective N = 1 , D = 4 SUGRA by dimensional reduction, that results in a Coleman–Weinberg type Galileon potential. We employ this potential in modeling inflation and in subsequent study of primordial quantum fluctuations for scalar and tensor modes. Further, we estimate the major observable parameters in both de Sitter ( DS ) and beyond de Sitter ( BDS ) limits and confront them with recent observational data from WMAP7 by using the publicly available code CAMB.
56054159
An accurate bound on tensor-to-scalar ratio and the scale of inflation
Abstract In this paper we provide an accurate bound on primordial gravitational waves, i.e. tensor-to-scalar ratio ( r ) for a general class of single-field models of inflation where inflation occurs always below the Planck scale, and the field displacement during inflation remains sub-Planckian. If inflation has to make connection with the real particle physics framework then it must be explained within an effective field theory description where it can be trustable below the UV cut-off of the scale of gravity. We provide an analytical estimation and estimate the largest possible r , i.e. r ⩽ 0.12 , for the field displacement less than the Planck cut-off.
197509411
Large non-Gaussianities from DBI Galileon and resolution of sensitivity problem
We have studied primordial non-Gaussian features through bispectrum and trispectrum analysis from a model of potential driven DBI Galileon inflation originating from background supergravity and Gauss-Bonnet terms.We have explicitly shown the violation of the widely accepted Maldacena theorem and standard Suyama-Yamaguchi relation in squeezed limit configuration which leads to the resolution of the well-known sensitivity problem between the non-Gaussian parameters ($f_{NL},\tau_{NL},g_{NL}$) and tensor to scalar ratio($r$). Our analysis thus overcomes a generic drawback of the wide class of DBI inflationary models which was, of late, facing tension from observational ground.Hence large primordial non-Gaussianities can be obtained even from single field DBI Galileon and hence these class of models can be directly confronted with the forthcoming results of PLANCK.
115768362
Collider constraints on Gauss-Bonnet coupling in warped geometry model
In this paper the requirement of a warp solution in an Einstein-Gauss-Bonnet 5D warped geometry is shown to fix the signature of Gauss-Bonnet coupling ($\alpha_{5}$). Further, imposing the phenomenological constraints, obtained from the recently observed Higgs like scalar mass as well as $\mu$ parameter of the decay channels ${H}_{0}\rightarrow\gamma\gamma,\tau{\bar \tau}$ explored in ATLAS and CMS detectors, we obtain a stringent bound on $\alpha_{5}$ within $(4.8 - 5.1)\times 10^{-7}$.