Frank J. Petriello

High-precision QCD at hadron colliders: Electroweak gauge boson rapidity distributions at next-to-next-to leading order

We compute the rapidity distributions of W and Z bosons produced at the Tevatron and the LHC through next-to-next-to leading order in QCD. Our results demonstrate remarkable stability with respect to variations of the factorization and renormalization scales for all values of rapidity accessible in current and future experiments. These processes are therefore gold-plated: current theoretical knowledge yields QCD predictions accurate to better than one percent. These results strengthen the proposal to use

Constraining the Littlest Higgs

W

Signals for noncommutative interactions at linear colliders

and

Kaluza-Klein Effects on Higgs Physics in Universal Extra Dimensions

Z

Precision Measurements and Fermion Geography in the Randall-Sundrum Model Revisited

production to determine parton-parton luminosities and constrain parton distribution functions at the LHC. For example, LHC data should easily be able to distinguish the central parton distribution fit obtained by MRST from that obtained by Alekhin.

Noncommutativity and unitarity violation in gauge boson scattering

Little Higgs models offer a new way to address the hierarchy problem, and give rise to a weakly-coupled Higgs sector. These theories predict the existence of new states which are necessary to cancel the quadratic divergences of the Standard Model. The simplest version of these models, the Littlest Higgs, is based on an SU(5)/SO(5) non-linear sigma model and predicts that four new gauge bosons, a weak isosinglet quark, t{prime}, with Q=2/3, as well as an isotriplet scalar field exist at the TeV scale. We consider the contributions of these new states to precision electroweak observables, and examine their production at the Tevatron. We thoroughly explore the parameter space of this model and find that small regions are allowed by the precision data where the model parameters take on their natural values. These regions are, however, excluded by the Tevatron data. Combined, the direct and indirect effects of these new states constrain the decay constant f {approx}> 3.5 TeV and m{sub t{prime}} {approx}> 10 TeV. These bounds imply that significant fine-tuning be present in order for this model to resolve the hierarchy problem.

The Higgs mechanism in non-commutative gauge theories

Recent theoretical results have demonstrated that non-commutative geometries naturally appear within the context of string/M-theory. One consequence of this possibility is that QED takes on a non-abelian nature due to the introduction of 3- and 4-point functions. In addition, each QED vertex acquires a momentum dependent phase factor. We parameterize the effects of non-commutative space-time co-ordinates and show that they lead to observable signatures in several 2 {yields} 2 QED processes in e{sup +}e{sup -} collisions. In particular, we examine pair annihilation, Moller and Bhabha scattering, as well as {gamma}{gamma} {yields} {gamma}{gamma} scattering and show that non-commutative scales of order a TeV can be probed at high energy linear colliders.

Radiative corrections to fixed target Moller scattering including hard bremsstrahlung effects

We examine the virtual effects of Kaluza-Klein (KK) states on Higgs physics in universal extra dimension models. We study the partial widths Γh→gg, Γh→γγ, and Γh→γZ, which are relevant for Higgs production and detection in future collider experiments. These interactions occur at one loop in the Standard Model, as do the KK contributions. We find that the deviations induced by the KK exchanges can be significant; for one extra dimension, the gg→h production rate is increased by 10%−85% for the meass of the first KK state in the range 500 m11500 GeV, a region untested by current direct search and precision measurement constraints. The h→γγ decay width is decreased by 20% in the same mass range. For two or more universal extra dimensions the results are cutoff dependent, and can only be qualitatively estimated. We comment on the detectability of these shifts at the LHC and at future e+e− and γγ colliders.

Photon photon and electron photon colliders with energies below a TeV

We re-examine the implications of allowing fermion fields to propagate in the five-dimensional bulk of the Randall-Sundrum (RS) localized gravity model. We find that the large mixing between the Standard Model top quark and its Kaluza Klein excitations restricts the fundamental RS scale to lie above 100 TeV. To circumvent this difficulty we propose a mixed scenario which localizes the third generation fermions on the TeV brane and allows the lighter generations to propagate in the full five-dimensional bulk. We show that this construction naturally reproduces the observed m{sub c}/m{sub t} and m{sub s}/m{sub b} hierarchies. We explore the signatures of this scenario in precision measurements and future high energy experiments. We find that the same region of parameter space that addresses the hierarchies of fermion Yukawa couplings also permits a Higgs boson with a mass of 500 GeV, and remains otherwise invisible at the LHC; however, the entire parameter region consistent with the electroweak precision data is testable at future linear colliders. We briefly discuss possible constraints on this scenario arising from flavor changing neutral currents.

Indirect Signatures of CP Violation in the Processes {gamma}{gamma} {yields} {gamma}{gamma}, {gamma}Z, and ZZ

We examine the unitarity properties of spontaneously broken noncommutative gauge theories. We find that the symmetry breaking mechanism in the noncommutative standard model of Chaichian et al. leads to an unavoidable violation of tree-level unitarity in gauge boson scattering at high energies. We then study a variety of simplified spontaneously broken noncommutative theories and isolate the source of this unitarity violation. Given the group theoretic restrictions endemic to noncommutative model building, we conclude that it is difficult to build a noncommutative standard model under the Weyl-Moyal approach that preserves unitarity.