635 research outputs found

### 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

### 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

### Minimal Subtraction vs. Physical Factorisation Schemes in Small-x QCD

We investigate the relationship of ``physical'' parton densities defined by
kt-factorisation, to those in the minimal subtraction scheme, by comparing
their small-x behaviour. We first summarize recent results on the above scheme
change derived from the BFKL equation at NLx level, and we then propose a
simple extension to the renormalisation-group improved (RGI) equation. In this
way we are able the examine the difference between resummed gluon distributions
in the Q_0 and MSbar schemes and also to show MSbar scheme resummed results for
P_gg and approximate ones for P_qg. We find that, due to the stability of the
RGI approach, small-x resummation effects are not much affected by the
scheme-change in the gluon channel, while they are relatively more sensitive
for the quark-gluon mixing.Comment: 14 pages, 8 figure

### 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

### A solvable model for small-x physics in D > 4 dimensions

I present a simplified model for the gluon Green's function governing
high-energy QCD dynamics, in arbitrary space-time dimensions. The BFKL integral
equation (either with or without running coupling) reduces to a second order
differential equation that can be solved in terms of Bessel and hypergeometric
functions. Explicit expressions for the gluon density and its anomalous
dimension are derived in MS and Q_0 factorization schemes. This analysis
illustrates the qualitative features of the QCD gluon density in both
factorization schemes. In addition, it clarifies the mathematical properties
and validates the results of the ``gamma-representation'' method proposed by
M.Ciafaloni and myself for extracting resummed next-to-leading-log x anomalous
dimensions of phenomenological relevance in the two schemes.Comment: 30 pages, 9 figure

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