99 research outputs found
Infrared Sensitive Physics in QCD and in Electroweak Theory
I recall the main ideas about the treatment of QCD infrared physics, as
developed in the late seventies, and I outline some novel applications of those
ideas to Electroweak Theory.Comment: 8 pages, to be published in the volume "String Theory of Fundamental
Interactions", published on the 65-th birthday of Gabriele Veneziano, M.
Gasperini and J. Maharana editors (Springer, Berlin Heidelberg, 2007
k-Factorization
I review the k-factorization method to combine the high-energy behaviour in
QCD with the renormalization group. Resummation formulas for coefficient
functions and anomalous dimensions are derived, and their applications to
small-x scaling violations in structure functions are briefly discussed.Comment: Latex file, 9 page
Energy Scale and Coherence Effects in small-x Equations
I consider the next-to-leading,high-energy cluster expansion of large-k
double-jet production in QCD, and I determine the corresponding one-loop quark
and gluon impact factors, for a self-consistent energy scale. The result shows
that coherent angular ordering of emitted gluons holds for hard emission also,
and singles out a scale which is essentially the largest virtuality in the
process. Both remarks are relevant for the precise deter- mination of the BFKL
kernel at the next-to-leading level.Comment: Figure available on reques
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
Radiation enhancement and "temperature" in the collapse regime of gravitational scattering
We generalize the semiclassical treatment of graviton radiation to
gravitational scattering at very large energies and finite
scattering angles , so as to approach the collapse regime of impact
parameters . Our basic tool is the
extension of the recently proposed, unified form of radiation to the ACV
reduced-action model and to its resummed-eikonal exchange. By superimposing
that radiation all-over eikonal scattering, we are able to derive the
corresponding (unitary) coherent-state operator. The resulting graviton
spectrum, tuned on the gravitational radius , fully agrees with previous
calculations for small angles but, for sizeable angles
acquires an exponential cutoff of the large
region, due to energy conservation, so as to emit a finite fraction
of the total energy. In the approach-to-collapse regime of we find
a radiation enhancement due to large tidal forces, so that the whole energy is
radiated off, with a large multiplicity and a
well-defined frequency cutoff of order . The latter corresponds to the
Hawking temperature for a black hole of mass notably smaller than .Comment: 35 pages, 18 figure
Unitarity restoring graviton radiation in the collapse regime of scattering
We investigate graviton radiation in gravitational scattering at small impact
parameters and extreme energies , a regime
in which classical collapse is thought to occur, and thus radiation may be
suppressed also. Here however, by analyzing the soft-based representation of
radiation recently proposed in the semiclassical ACV framework, we argue that
gravitons can be efficiently produced in the untrapped region
, so as to suggest a possible completion of the
unitarity sum. In fact, such energy radiation at large distances turns out to
compensate and to gradually reduce to nothing the amount of energy being
trapped at small-'s, by thus avoiding the quantum tunneling suppression of
the elastic scattering and suggesting a unitary evolution. We finally look at
the coherent radiation sample so obtained and we find that, by energy
conservation, it develops an exponential frequency damping corresponding to a
"quasi-temperature" of order , which is naturally related to a Hawking
radiation and is suggestive of a black-hole signal at quantum level.Comment: 13 pages, 3 figure
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