arXiv subjects

Scott Willenbrock

Publications and source records attributed to Scott Willenbrock.

28 records · Page 2Linked to original sources

arXiv2007

Dimension-Five Operators in Grand Unified Theories

Extensions of the standard model with low-energy supersymmetry generically allow baryon- and lepton-number violating operators of dimension four and five, yielding rapid proton decay. The dimension-four operators are usually forbidden by matter parity. We investigate to what extent the appearance of dimension-five operators at the Planck scale may be constrained by the different grand-unified gauge groups. Dimension-five operators are suppressed in models based on E_6 and SU(3)_C x SU(3)_L x SU(3)_R, where four matter fields do not form a gauge singlet. An intermediate scale offers the possibility to sufficiently suppress these dimension-five operators.

hep-ph↗

arXiv2006

Higgs at the Tevatron in Extended Supersymmetric Models

Supersymmetric models with an additional singlet field offer the Higgs boson the possibility to decay to two pseudoscalars, a. If the mass of these pseudoscalars is above the b bbar threshold, a -> b bbar is generically the dominant decay mode. The decay h -> a a -> b bbar b bbar may be seen above backgrounds at the Tevatron if the Higgs production cross section is enhanced relative to that of the standard model.

hep-ph↗

arXiv2005

Inclusive production of a Higgs or Z boson in association with heavy quarks

We calculate the cross section for the production of a Z boson in association with heavy quarks. We suggest that this cross section can be measured using an inclusive heavy-quark tagging technique. This could be used as a feasibility study for the search for a Higgs boson produced in association with bottom quarks. We argue that the best formalism for calculating that cross section is based on the leading-order process b b -> h, and that it is valid for all Higgs masses of interest at both the Fermilab Tevatron and the CERN Large Hadron Collider.

hep-ph↗

arXiv2005

Scale of Quantum Gravity

In the effective field theory of quantum gravitation coupled to N_s scalars, N_f fermions, and N_V vectors, tree unitarity is violated at an energy squared of E_{CM}^2 = 20(G_N N)^{-1}, where N = {2/3}N_s + N_f + 4N_V and G_N is Newton's constant. This is related to radiative corrections proportional to G_N N E^2 (where E is the typical energy), due to loops of such particles. New physics must enter before E_{CM}=5.6 x 10^{18} GeV in the standard model, and 4.6 x 10^{18} GeV in the minimal supersymmetric standard model.

hep-ph↗

arXiv2005

Symmetries of the Standard Model

I present an overview of the standard model, concentrating on its global continuous symmetries, both exact and approximate. There are four lectures, dedicated to spacetime symmetry, flavor symmetry, custodial symmetry, and scale symmetry. Topics include Weyl, Majorana, and Dirac spinors; massive neutrinos; electroweak symmetry breaking; effective field theory; and the hierarchy problem.

hep-ph↗

arXiv2005

Angular momentum content of a virtual graviton

We show that a virtual graviton has a J=0 component, which serves to cancel the J=2, J_z=0 component when the graviton is on shell. In contrast, a massive graviton has no J=0 component either on or off shell. This difference is responsible for the van Dam-Veltman-Zakharov discontinuity.

hep-ph↗

arXiv2002

Hadron Colliders, the Standard Model, and Beyond

I argue that the Fermilab Tevatron will contribute to our knowledge of the pieces of the standard model that we know the least about. I discuss five of the most important areas in which the Tevatron can confront the standard model: precision electroweak, CKM, top quark, Higgs, and QCD. I then review the evidence, both direct and indirect, for physics beyond the standard model.

hep-ph↗

arXiv1996

Ruling Out a Strongly-Interacting Standard Higgs Model

Previous work has suggested that perturbation theory is unreliable for Higgs- and Goldstone-boson scattering, at energies above the Higgs mass, for relatively small values of the Higgs quartic coupling $λ(μ)$. By performing a summation of nonlogarithmic terms, we show that perturbation theory is in fact reliable up to relatively large coupling. This eliminates the possibility of a strongly-interacting standard Higgs model at energies above the Higgs mass, complementing earlier studies which excluded strong interactions at energies near the Higgs mass. The summation can be formulated in terms of an appropriate scale in the running coupling, $μ=\sqrt{s}/e\approx\sqrt{s}/2.7$, so it can easily be incorporated in renormalization-group improved tree-level amplitudes as well as higher-order calculations.

hep-ph↗

arXiv1993

Planck-Scale Unification and Dynamical Symmetry Breaking

We explore the possibility of unification of gauge couplings near the Planck scale in models of extended technicolor. We observe that models of the form G X SU(3)_c X SU(2)_L X U(1)_Y cannot be realized, due to the presence of massless neutral Goldstone bosons (axions) and light charged pseudo-Goldstone bosons; thus, unification of the known forces near the Planck scale cannot be achieved. The next simplest possibility, G X SU(4)_{PS} X SU(2)_L X U(1)_{T_{3R}}, cannot lead to unification of the Pati-Salam and weak gauge groups near the Planck scale. However, superstring theory provides relations between couplings at the Planck scale without the need for an underlying grand-unified gauge group, which allows unification of the SU(4)$_{PS}$ and SU(2)$_L$ couplings.

hep-ph↗

arXiv1993

Yukawa correction to top-quark production at the Tevatron

We calculate the correction to $\qbq\to\tbt$ of order $\gmm$. This correction, proportional to the square of the Higgs-boson Yukawa coupling to the top quark, arises from loops of Higgs bosons and the scalar component of virtual vector bosons. The Yukawa correction to the total \tbt\ production cross section at the Fermilab Tevatron in the standard Higgs model is found to be much less than the theoretical uncertainty in the cross section. However, in a two-Higgs-doublet model, Yukawa couplings are generally enhanced. The Yukawa correction can increase the total $t\bar t$ production cross section in this model by as much as $20$-$35\%$, which is potentially observable at the Tevatron.

hep-ph↗