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.Comment: 14 page

Top Pair Forward-Backward Asymmetry from Loops of New Strongly Coupled Quarks

We examine loop-mediated effects of new heavy quarks Q=(t',b') on t tbar production at hadron colliders, using a phenomenological model with flavor off-diagonal couplings of charged and neutral scalars phi=(phi^+-,phi^0) to Q. We show that an invariant-mass-dependent asymmetry, in the t tbar center of mass, consistent with those recently reported by the CDF collaboration can be obtained for quark masses around 350-500 GeV, scalar masses of order 100-200 GeV, and modest to strong Yukawa couplings. The requisite strong interactions suggest a non-perturbative electroweak symmetry breaking mechanism and composite states at the weak scale. A typical prediction of this framework is that the new heavy quarks decay dominantly into t phi final states.Comment: 6 pages 6 figures; version published in Physical Review

Choosing the Factorization Scale in Perturbative QCD

We define the collinear factorization scheme, which absorbs only the collinear physics into the parton distribution functions. In order to isolate the collinear physics, we introduce a procedure to combine real and virtual corrections, canceling infrared singularities prior to integration. In the collinear scheme, the factorization scale $\mu$ has a simple physical interpretation as a collinear cutoff. We present a method for choosing the factorization scale and apply it to the Drell-Yan process; we find $\mu \approx Q/2$, where $Q$ is the vector-boson invariant mass. We show that, for a wide variety of collision energies and $Q$, the radiative corrections are small in the collinear scheme for this choice of factorization scale.Comment: 25 pages, 18 figure

Grand Unification and Light Color-Octet Scalars at the LHC

We study the properties and production mechanisms of color-octet scalars at the LHC. We focus on the single production of both charged and neutral members of an (8,2)_1/2 doublet through bottom quark initial states. These channels provide a window to the underlying Yukawa structure of the scalar sector. Color-octet scalars naturally appear in grand unified theories based on the SU(5) gauge symmetry. In the context of adjoint SU(5) these fields are expected to be light to satisfy constraints coming from unification and proton decay, and may have TeV-scale masses. One combination of their couplings is defined by the relation between the down-quark and charged-lepton Yukawa couplings. Observation of these states at the LHC gives an upper bound on the proton lifetime if they truly arise from this grand unified theory. We demonstrate that TeV-mass scalars can be observed over background at the LHC using boosted top quark final states, and study how well the scalar Yukawa parameters can be measured.Comment: 22 pages, LaTeX, 5 figures; typos corrected, references adde

Precocious Diphoton Signals of the Little Radion at Hadron Colliders

In Little Randall-Sundrum models, the bulk couplings of the radion to massless gauge fields can yield a greatly enhanced diphoton signal at hadron colliders. We examine the implications of the Tevatron data for the Little radion and also show that the 7 TeV run at the Large Hadron Collider will have an impressive reach in this channel. The diphoton signal is crucial in the search for a light radion, or the dual dilaton, and can potentially probe the ultraviolet scale of the theory.Comment: 5 pages, 2 figures. Errors in the WW and ZZ branching fraction curves in Fig.1 and the related numerical results in Fig.2 have been corrected. New references have been added. Our main conclusions regarding the enhanced diphoton signal of the Little radion remain qualitatively the same and quantitatively similar to the previous result

The Radion as a Harbinger of Deca-TeV Physics

Precision data generally require the threshold for physics beyond the Standard Model to be at the deca-TeV (10 TeV) scale or higher. This raises the question of whether there are interesting deca-TeV models for which the LHC may find direct clues. A possible scenario for such physics is a 5D warped model of fermion masses and mixing, with Kaluza-Klein masses m_KK ~ 10 TeV, allowing it to avoid tension with stringent constraints, especially from flavor data. Discovery of a Standard-Model-like Higgs boson, for which there are some hints at ~125 GeV at the LHC, would also require the KK masses to be at or above 10 TeV. These warped models generically predict the appearance of a much lighter radion scalar. We find that, in viable warped models of flavor, a radion with a mass of a few hundred GeV and an inverse coupling of order m_KK ~ 10 TeV could typically be accessible to the LHC experiments -- with sqrt(s) = 14 TeV and 100 fb^-1 of data. The above statements can be applied, mutatis mutandis, to 4D dual models, where conformal dynamics and a dilaton replace warping and the radion, respectively. Detection of such a light and narrow scalar could thus herald the proximity of a new physical threshold and motivate experiments that would directly probe the deca-TeV mass scale.Comment: 18 pages, 5 figures; version published in Physical Review

Nursing brain drain from India

In response to recent findings regarding migration of health workers out of Africa, we provide data from a survey of Indian nurses suggesting that up to one fifth of the nursing labour force may be lost to wealthier countries through circular migration

QCD Corrections to Scalar Diquark Production at Hadron Colliders

We calculate the next-to-leading order QCD corrections to quark-quark annihilation to a scalar resonant state ("diquark") in a color representation of antitriplet or sextet at the Tevatron and LHC energies. At the LHC, we find the enhancement (K-factor) for the antitriplet diquark is typically about 1.31--1.35, and for the sextet diquark is about 1.22--1.32 for initial-state valence quarks. The full transverse-momentum spectrum for the diquarks is also calculated at the LHC by performing the soft gluon resummation to the leading logarithm and all orders in the strong coupling.Comment: 24 pages, 17 figure

Collinear singularities and the factorization scale in perturbative QCD

We discuss several issues related to collinear singularities and the choice of the factorization scale in perturbative QCD calculations. First, we argue in favor of the use of a bottom-quark distribution function, which sums collinear logarithms, in the calculation of the cross section for Higgs-boson production in association with bottom quarks. As a testing ground for Higgs searches, we propose a measurement of Z-boson production in association with heavy quarks, using an inclusive heavy-quark tagging technique. Next, we present a calculation of the next-to-leading-order QCD corrections to Drell-Yan production of a W boson, regulating the collinear singularities with a nonzero quark mass and the infrared and ultraviolet singularities with dimensional regularization. Finally, we present the collinear factorization scheme, in which only collinear physics is absorbed into the parton distribution functions. We provide a physically motivated method for choosing the factorization scale in this scheme, and show, for the case of Drell-Yan production of an electroweak gauge boson, that the next-to-leading-order QCD corrections are very small for this choice of factorization scale.U of I OnlyPost 1923. No authorization form