1,422 research outputs found
QCD factorization with heavy quarks
We further analyze the definition and the calculation of the heavy quark
impact factor at next-to-leading (NL) level, and we provide its
analytical expression in a previously proposed k-factorization scheme. Our
results indicate that k-factorization holds at NL level with a properly chosen
energy scale, and with the same gluonic Green's function previously found in
the massless probe case.Comment: LaTeX2e, 4pp, 2 figures, uses espcrc2.sty. Talk given at
International Workshop on Diffraction in High-Energy Physics (Diffraction
2000), Cetraro, Italy, Sept. 2-7, 2000. The complete paper is also available
at http://www-ttp.physik.uni-karlsruhe.de/Preprints
Electroweak double logarithms in inclusive observables for a generic initial state
High energy observables are characterized by large electroweak radiative
corrections of infrared origin; double logarithms are present even for
inclusive cross sections, thus violating the Bloch Nordsieck theorem. This
effect, related to the initial states carrying nonabelian isospin charges, is
here investigated for {\sl any} inclusive cross section in the
SU(2)U(1) symmetric limit, that is appropriate for energies much
higher than the weak scale. We develop a general formalism allowing to
calculate the all order double log resummed cross sections once the hard (tree
level) ones are known. The relevant cases of fermion-fermion, fermion-boson and
boson-boson scattering are discussed.Comment: 6 pages, 2 figure
Enhanced Electroweak Corrections to Inclusive Boson Fusion Processes at the TeV Scale
Electroweak radiative corrections with double-log enhancements occur in
inclusive observables at the TeV scale because of a lack of compensation of
virtual corrections with real emission due to the nonabelian (weak isospin)
charges of the accelerator beams. Here we evaluate such Bloch-Nordsieck
violating corrections in the case of initial longitudinal bosons, which is
experimentally provided by boson fusion processes, and is related to the
Goldstone-Higgs sector. All four states of this sector are involved in the
group structure of the corrections, and cause in particular a novel double log
effect due to hypercharge mixing in the longitudinal states. We study both the
light- and the heavy-Higgs cases, and we analyze the symmetry breaking pattern
of the corrections. The latter turn out to be pretty large, in the 5-10 %
range, and show an interesting Higgs mass dependence, even for processes
without Higgs boson in the final state.Comment: 15 pages, 6 figure
Diffusion corrections to the hard pomeron
The high-energy behaviour of two-scale hard processes is investigated in the
framework of small-x models with running coupling, having the Airy diffusion
model as prototype. We show that, in some intermediate high-energy regime, the
perturbative hard Pomeron exponent determines the energy dependence, and we
prove that diffusion corrections have the form hinted at before in particular
cases. We also discuss the breakdown of such regime at very large energies, and
the onset of the non-perturbative Pomeron behaviour.Comment: 18 pages, 3 Postscript figure
All Order Running Coupling BFKL Evolution from GLAP (and vice-versa)
We present a systematic formalism for the derivation of the kernel of the
BFKL equation from that of the GLAP equation and conversely to any given order,
with full inclusion of the running of the coupling. The running coupling is
treated as an operator, reducing the inclusion of running coupling effects and
their factorization to a purely algebraic problem. We show how the GLAP
anomalous dimensions which resum large logs of x can be derived from the
running-coupling BFKL kernel order by order, thereby obtaining a constructive
all-order proof of small x factorization. We check this result by explicitly
calculating the running coupling contributions to GLAP anomalous dimensions up
to next-to-next-to leading order. We finally derive an explicit expression for
BFKL kernels which resum large logs of Q^2 up to next-to-leading order from the
corresponding GLAP kernels, thus making possible a consistent collinear
improvement of the BFKL equation up to the same order
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
Can we trust small x resummation?
We review the current status of small x resummation of evolution of parton
distributions and of deep-inelastic coefficient functions. We show that the
resummed perturbative expansion is stable, robust upon different treatments of
subleading terms, and that it matches smoothly to the unresummed perturbative
expansions, with corrections which are of the same order as the typical NNLO
ones in the HERA kinematic region. We discuss different approaches to small x
resummation: we show that the ambiguities in the resummation procedure are
small, provided all parametrically enhanced terms are included in the
resummation and properly matched.Comment: 12 pages, 12 figures; LaTeX with espcrc2.sty. Talk given at the 2008
Ringberg workshop "New Trends in HERA Physics
Electroweak Bloch-Nordsieck violation at the TeV scale: "strong" weak interactions ?
Hard processes at the TeV scale exhibit enhanced (double log) EW corrections
even for inclusive observables, leading to violation of the Bloch-Nordsieck
theorem. This effect, previously related to the non abelian nature of free EW
charges in the initial state (e- e+, e- p, p p ...), is here investigated for
fermion initiated hard processes and to all orders in EW couplings. We find
that the effect is important, especially for lepton initiated processes,
producing weak effects that in some cases compete in magnitude with the strong
ones. We show that this (double log) BN violating effect has a universal energy
dependence, related to the Sudakov form factor in the adjoint representation.
The role of this form factor is to suppress cross section differences within a
weak isospin doublet, so that at very large energy the cross sections for
left-handed electron-positron and neutrino-positron scattering become equal.
Finally, we briefly discuss the phenomenological relevance of our results for
future colliders.Comment: 18 pages, 6 figures, uses epsfig.sty and subequation.st
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