518 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
Infrared weak corrections to strongly interacting gauge bosons scattering
We evaluate the impact of electroweak corrections of infrared origin on
longitudinal strongly interacting gauge bosons scattering, calculating all
order resummed expressions at the double log level. As a working example, we
consider the Standard model with a heavy Higgs. At energies typical of
forthcoming experiments (LHC,ILC,CLIC), the corrections are in the 10-40 %
range, the relative sign depending on the initial state considered and on
whether or not additional gauge bosons emission is included.Comment: 13 pages, 6 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
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
Bloch-Nordsieck violating electroweak corrections to inclusive TeV scale hard processes
We point out that, since the colliders initial states (e+ e-,p p, p pbar, ...
) carry a definite nonabelian flavor, electroweak radiative corrections to
inclusive hard cross sections at the TeV scale are affected by peculiar
Bloch-Nordsieck violating double logs. We recall the setup of soft cancellation
theorems, and we analyze the magnitude of the noncancelling terms in the
example of electron - positron annihilation into hadrons.Comment: Minor typos corrected, references added. Final version to appear on
Phys. Rev. Let
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
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
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