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

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

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 $\sqrt{s}\gg m_P$ and finite scattering angles $\Theta_s$, so as to approach the collapse regime of impact parameters $b \simeq b_c \sim R\equiv 2G\sqrt{s}$. 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 $R$, fully agrees with previous calculations for small angles $\Theta_s\ll 1$ but, for sizeable angles $\Theta_s(b)\leq \Theta_c = O(1)$ acquires an exponential cutoff of the large $\omega R$ region, due to energy conservation, so as to emit a finite fraction of the total energy. In the approach-to-collapse regime of $b\to b_c^+$ we find a radiation enhancement due to large tidal forces, so that the whole energy is radiated off, with a large multiplicity $\langle N \rangle\sim Gs \gg 1$ and a well-defined frequency cutoff of order $R^{-1}$. The latter corresponds to the Hawking temperature for a black hole of mass notably smaller than $\sqrt{s}$.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 $b<R\equiv 2G\sqrt{s}$ and extreme energies $s\gg M_P^2$, 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 $|\boldsymbol{x}|\gtrsim R>b$, 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 $E'$ being trapped at small-$b$'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 $\hbar/R$, which is naturally related to a Hawking radiation and is suggestive of a black-hole signal at quantum level.Comment: 13 pages, 3 figure