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P. Ciafaloni

Publications and source records attributed to P. Ciafaloni.

17 recordsLinked to original sources
arXiv2009

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.

hep-ph↗
arXiv2008

Electroweak double-logs at small x

We investigate enhanced EW corrections to inclusive hard processes in the TeV energy region with emphasis on the small-x situation, in which the hard scale Q is significantly smaller than the available energy \sqrt{s}= Q/x. We first propose and justify a general factorization formula in which the (double-log) EW form factor at scale Q^2 is factorized from EW parton distribution functions, which satisfy evolution equations of DGLAP type. We then investigate the small-x behavior of the EW parton distributions including the novel ones for non-vanishing t-channel weak isospin T and we compare it with a BFKL-type approach. In either approach we find that large small-x corrections of order α_w \log x \log Q^2/M^2 (M being the EW symmetry breaking scale) are present only for T=2 and not for T=1. This implies that only transverse WW interactions (coupled to T=2) are affected, while the T=1 components feel just the form factor at scale Q^2.

hep-ph↗
arXiv2003

Sudakov Electroweak effects in transversely polarized beams

We study Standard Model electroweak radiative corrections for fully inclusive observables with polarized fermionic beams. Our calculations are relevant in view of the possibility for Next Generation Linear colliders of having transversely and/or longitudinally polarized beams. The case of initial transverse polarization is particularly interesting because of the interplay of infrared/collinear logarithms of different origins, related both to the nonabelian SU(2) and abelian U(1) sectors. The Standard model effects turn out to be in the 10% range at the TeV scale, therefore particularly relevant in order to disentangle possible New Physics effects.

hep-ph↗
arXiv2001

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.

hep-ph↗
arXiv2000

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)$\otimes$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.

hep-ph↗
arXiv2000

TeV scale weak interactions: inclusive vs. exclusive observables

Hard processes at the TeV scale exhibit enhanced (double log) EW corrections, that need resummation in view of the high level of precision of Next Linear Colliders. The fact that the weak sector is spontaneously broken causes some peculiarities with respect to unbroken theories like QCD. For observables that are exclusive with respect to $W,Z$ emission, some peculiar technical problems have yet to be solved. Surprisingly, double logarithmic enhancements are present even for inclusive observables like $e^+e^-\to$ hadrons, leading to violation of the Bloch-Nordsieck theorem. The last effect is particularly important, producing weak effects that in some cases compete in magnitude with the strong ones.

hep-ph↗
arXiv2000

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.

hep-ph↗
arXiv2000

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.

hep-ph↗
arXiv1999

Logarithmic expansion of electroweak corrections to four-fermion processes in the TeV region

Starting from a theoretical representation of the electroweak component of four-fermion neutral current processes that uses as theoretical input the experimental measurements at the Z peak, we consider the asymptotic high energy behaviour in the Standard Model at one loop of those gauge-invariant combinations of self-energies, vertices and boxes that contribute all the different observables. We find that the logarithmic contribution due to the renormalization group running of the various couplings is numerically overwhelmed by single and double logarithmic terms of purely electroweak (Sudakov-type) origin, whose separate relative effects grow with energy, reaching the 10% size at about one TeV. We then propose a simple "effective" parametrization that aims at describing the various observables in the TeV region, and discuss its validity both beyond and below 1 TeV, in particular in the expected energy range of future linear electron-positron (LC) and muon-muon colliders.

hep-ph↗
arXiv1999

Electroweak Sudakov form factors and nonfactorizable soft QED effects at NLC energies

We study the leading log infrared behavior of electroweak corrections at TeV scale energies, that will be reached by next generation of linear colliders (NLC). We show that, contrary to what happens at typical LEP energies, it is not anymore possible to disentangle ``pure electroweak'' from ``photonic'' corrections. This means that soft QED effects do not factorize and therefore cannot be treated in the usual ``naive'' way they were accounted for in the LEP-era. The nonfactorizable effects come up first at the two loop LL level, that we calculate explicitly for a fermion source that is neutral under the SU(2)$\otimes$U(1) gauge group (explicitly, a Z' decay into two fermions). The basic formalism we set up can be used to calculate LL effects at any order of perturbation theory. The results of this paper might be important for future calculations of electroweak corrections at NLC energies.

hep-ph↗
arXiv1999

The role of the top mass in b-production at future lepton colliders

We compute the one loop contribution coming from vertex and box diagrams, where virtual top quarks are exchanged, to the asymptotic energy behaviour of $b\bar b$ pair production at future lepton colliders. We find that the effect of the top mass is an extra linear logarithmic term of Sudakov type that is not present in the case of (u,d,s,c) production. This appears to be particularly relevant in the case of the $b\bar{b}$ cross section.

hep-ph↗
arXiv1999

Susy Virtual effects at LEP2 Boundary

We examine the possibility that SUSY particles are light, i.e. have a mass just beyond the final kinematical reach of LEP2. In this case, even if light particles are not directly detected, their virtual effects are enhanced by a ``close to threshold'' resonance in the s-channel. We find that this resonant effect is absent in the case of light sfermions, while it is enhanced in the case of light gauginos, since neutralinos and charginos add coherently in some regions of the allowed parameter space. We discuss this ``virtual-alliance'' in detail and try to examine the possibilities of its experimental verification.

hep-ph↗
arXiv1999

Sudakov Effects in Electroweak Corrections

In perturbation theory the infrared structure of the electroweak interactions produces large corrections proportional to double logarithms log^2 (s/m^2), similar to Sudakov logarithms in QED, when the scale s is much larger than the typical mass m of the particles running in the loops. These energy growing corrections can be particularly relevant for the planned Next Linear Colliders. We study these effects in the Standard Model for the process e+ e^->f fbar and we compare them with similar corrections coming from SUSY loops.

hep-ph↗
arXiv1997

Two-loop QCD corrections to charged-Higgs-mediated $b\to sγ$ decay

The charged-Higgs-mediated contribution to the Wilson coefficient of the $b\to sγ$ magnetic penguin is expected to be one of the more promising candidates for a supersymmetric effect in B physics, probably the only one in gauge-mediated models. We compute the two-loop QCD correction to it. With naive dimensional regularization and MSbar subtraction, for reasonable values of the charged Higgs mass and for mu-bar = m_top, we find a (10--20)% reduction of the corresponding one-loop effect.

hep-ph↗
arXiv1996

The Effective Lagrangian of the Two Higgs Doublet Model

We consider the two Higgs doublet model extension of the Standard Model in the limit where all physical scalar particles are very heavy; too heavy, in fact, to be experimentally produced in forthcoming experiments. The symmetry breaking sector can thus be described by an effective chiral Lagrangian. We obtain the values of the coefficients of the O(p^4) operators relevant to the oblique corrections and investigate to what extent some non-decoupling effects may remain at low energies.

hep-ph↗
arXiv1995

Light thresholds in Grand Unified Theories

In a generic Grand Unified Theory with a relatively small dispersion of the spectrum around the $Z$-boson and the unification masses, a connection is established, exact at one loop level, between $M_Z$, $G_{\rm F}$, $α(M_Z)$ and the strong coupling constant $α_3(M_Z)$. At this level of precision, this avoids the logical and phenomenological inconsistency of predicting $α_3(M_Z)$ by means of the electroweak couplings as extracted from the data in the Standard Model rather than in the complete theory. Attention is paid to the independence of the physical results from regularization and/or renormalization schemes. As a particularly relevant example, the analysis is specialized to the case of the Minimal Supersymmetric Standard Model, with emphasis on light charginos and neutralinos.

hep-ph↗