Electroweak lights from Dark Matter annihilations

The energy spectra of Standard Model particles originated from Dark Matter annihilations can be significantly altered by the inclusion of electroweak gauge boson radiation from the final state. A situation where this effect is particularly important is when a Majorana Dark Matter particle annihilates into two light fermions. This process is in p-wave and hence suppressed by the small value of the relative velocity of the annihilating particles. The inclusion of electroweak radiation eludes this suppression and opens up a potentially sizeable s-wave contribution to the annihilation cross section. I will discuss the impact of this effect on the fluxes of stable particles resulting from the Dark Matter annihilations, which are relevant for Dark Matter indirect searches.Comment: 4 pages, 2 figures. Contribution to the conference proceedings of TAUP 2011, Munich - Germany (5-9 September 2011

The BFKL Equation at Next-to-Leading Order and Beyond

On the basis of a renormalization group analysis of the kernel and of the solutions of the BFKL equation with subleading corrections, we propose and calculate a novel expansion of a properly defined effective eigenvalue function. We argue that in this formulation the collinear properties of the kernel are taken into account to all orders, and that the ensuing next-to-leading truncation provides a much more stable estimate of hard Pomeron and of resummed anomalous dimensions.Comment: LaTex, 12 pages, 1 eps figur

Towards Collinear Evolution Equations in Electroweak Theory

We consider electroweak radiative corrections to hard inclusive processes at the TeV scale, and we investigate how collinear logarithms factorize in a spontaneously broken gauge theory, similarly to the DGLAP analysis in QCD. Due to the uncancelled double logs noticed previously, we find a factorization pattern which is qualitatively different from the analogous one in QCD. New types of splitting functions emerge which are needed to describe the initial beam charges and are infrared-sensitive, that is dependent on an infrared cutoff provided, ultimately, by the symmetry breaking scale. We derive such splitting functions at one-loop level in the example of SU(2) gauge theory, and we also discuss the structure functions' evolution equations, under the assumption that isospin breaking terms present in the Ward identities of the theory are sufficiently subleading at higher orders.Comment: 5 pages, 3 figure

Quantum Tunneling and Unitarity Features of an S-matrix for Gravitational Collapse

Starting from the semiclassical reduced-action approach to transplanckian scattering by Amati, Veneziano and one of us and from our previous quantum extension of that model, we investigate the S-matrix expression for inelastic processes by extending to this case the tunneling features previously found in the region of classical gravitational collapse. The resulting model exhibits some non-unitary S-matrix eigenvalues for impact parameters b < b_c, a critical value of the order of the gravitational radius R = 2 G sqrt(s), thus showing that some (inelastic) unitarity defect is generally present, and can be studied quantitatively. We find that S-matrix unitarity for b < b_c is restored only if the rapidity phase-space parameter y is allowed to take values larger than the effective coupling G s / hbar itself. Some features of the resulting unitary model are discussed.Comment: 28 pages, 11 figure

Bloch-Nordsieck Violation in Spontaneously Broken Abelian Theories

We point out that, in a spontaneously broken U(1) gauge theory, inclusive processes, whose primary particles are mass eigenstates that do not coincide with the gauge eigenstates, are not free of infrared logarithms. The charge mixing allowed by symmetry breaking and the ensuing Bloch-Nordsieck violation are here analyzed in a few relevant cases and in particular for processes initiated by longitudinal gauge bosons. Of particular interest is the example of weak hypercharge in the Standard Model where, in addition, left-right mixing effects arise in transversely polarized fermion beams.Comment: 4 pages, 1 figur

Initial State Radiation in Majorana Dark Matter Annihilations

The cross section for a Majorana Dark Matter particle annihilating into light fermions is helicity suppressed. We show that, if the Dark Matter is the neutral Majorana component of a multiplet which is charged under the electroweak interactions of the Standard Model, the emission of gauge bosons from the initial state lifts the suppression and allows an s-wave annihilation. The resulting energy spectra of stable Standard Model particles are importantly affected. This has an impact on indirect searches for Dark Matter.Comment: 9 pages, 3 figure

A collinear model for small-x physics

We propose a simple model for studying small-x physics in which we take only the collinearly enhanced part of leading and subleading kernels, for all possible transverse momentum orderings. The small-x equation reduces to a second order differential equation in t=log k^2/Lambda^2 space, whose perturbative and strong-coupling features are investigated both analytically and numerically. For two-scale processes, we clarify the transition mechanism between the perturbative, non Regge regime and the strong-coupling Pomeron behavior.Comment: 22 pages, 8 figures, LaTeX file, uses JHEP.cl

Electroweak Sudakov Logarithms and Real Gauge-Boson Radiation in the TeV Region

Electroweak radiative corrections give rise to large negative, double-logarithmically enhanced corrections in the TeV region. These are partly compensated by real radiation and, moreover, affected by selecting isospin-noninvariant external states. We investigate the impact of real gauge boson radiation more quantitatively by considering different restricted final state configurations. We consider successively a massive abelian gauge theory, a spontaneously broken SU(2) theory and the electroweak Standard Model. We find that details of the choice of the phase space cuts, in particular whether a fraction of collinear and soft radiation is included, have a strong impact on the relative amount of real and virtual corrections.Comment: 20 pages, 4 figure

Tunneling transition to the Pomeron regime

We point out that, in some models of small-x hard processes, the transition to the Pomeron regime occurs through a sudden tunneling effect, rather than a slow diffusion process. We explain the basis for such a feature and we illustrate it for the BFKL equation with running coupling by gluon rapidity versus scale correlation plots.Comment: 17 pages, 5 figures, mpeg animations available from http://www.lpthe.jussieu.fr/~salam/tunneling/ . v2 includes additional reference