Benjamin Grinstein

Heavy Meson Form-factors From {QCD}

Abstract We calculate the leading QCD radiative corrections to the relations which follow from the decoupling of the heavy quark spin as the quark mass goes to infinity and from the symmetry between systems with different heavy quarks. One of the effects we calculate gives the leading q2-dependence of the form factor of a heavey quark, which in turn dominates the q2-dependence of the form factors of bound states of the heavy quark with light quarks. This, combined with the normalization of the form factor provided by symmetry, gives us a first principles calculation of the heavy meson (or baryon) form factors in the limit of very large heavy quark mass.

CP violation in the minimal N = 1 supergravity theory

Supersymmetric theories allow a variety of sources for CP violation. Radiative contributions to ϵ, ϵ′, p and the neutron electric dipole moment are considered in two versions of the minimal N = 1 supergravity theory. If the top quark is heavy, the superbox may dominate ϵ and limit s2s3sδ, thus suppressing contributions of sδ to ϵ′. Possibly large contributions to ϵ′ are considered which are independent of δ. An additional large contribution to the electric dipole moment of the neutron is pointed out. A proposal is put forward that may lead to a solution to the strong CP problem.

Lepton energy distributions in heavy meson decays from QCD

Abstract We use the techniques of an effective field theory for heavy quark systems to calculate inclusive lepton energy distributions in heavy meson decays. Our approach is patterned after the operator product expansion analysis of R in e+ −e− annihilation and deep inelastic electroproduction. We extend the idea of an operator product expansion to a situation in which we match the physics from a T-product in the high energy theory to a set of local operators in the low energy effective heavy quark field theory. In leading order we reproduce the results of the parton model, but we can also describe the corrections systematically. We are led to the rather surprising conclusion that there are no nonperturbative corrections of order mbΛQCD to the average invariant mass-squared of the final hadronic state.

The Static Quark Effective Theory

Processes involving one heavy quark at small momentum are of great phenomenological interest. The anomalous dependence on the heavy quark mass m of the amplitudes for these processes can be extracted using an effective theory with the heavy quark treated as a static color source. We prove the validity of this 1m expansion to leading order in 1m and to all orders in the loop expansion.

A Supersymmetric SU(5) Gauge Theory with No Gauge Hierarchy Problem

Abstract A supersymmetric unified model is proposed in which one obtains light Higgs doublets as required for SU(2)×U(1) breaking whose colored partners remain heavy. Every interaction term allowed by the assumed symmetries is included and in this sense the model is natural. Both the gauge symmetry and a global U(1) symmetry are broken at a scale of ⪆ 10 17 GeV and the effective low-energy gauge theory just corresponds to the supersymmetric standard model.

Strong Interaction Effects in Weak Radiative

Abstract Strong-interaction corrections to the effective hamiltonian for weak radiative B - meson decay (i.e., B → X s γ , where Xs denotes a strange hadronic final state) are calculated using the leading logarithmic approximation. The inclusive rate for decays B → X s γ , where the energy of the photon is large, is computed in the standard model with minimal particle content and in extensions of the minimal standard model with two Higgs doublets.

\bar{B}

Abstract The amplitudes for nonleptonic decays of heavy mesons are notoriously difficult to calculate. Factorization has been used in an attempt to transcribe results from model calculations of semileptonic decay rates of heavy mesons. We propose that factorization holds perturbatively in QCD, provided one looks in the appropriate kinematic regime. This is studied with the use of a novel expansion in which factorization holds in leading order, which includes all orders in the loop expansion. Our results are contrasted with large- N expansion arguments.

Meson Decay

We investigate the 1m corrections to the heavy quark effective theory, where m is the mass of a heavy quark. At this order new flavor conserving operators arise from the expansion of the kinetic energy in the full theory. Along with 1m corrections to the matching conditions, these operators induce corrections of order λQCDm to the flavor changing currents which mediate weak decays in the effective theory. We illustrate the calculation of the anomalous dimension matrix for such operators.

QCD basis for factorization in decays of heavy mesons

The impact of new physics associated with the Higgs sector on precision electroweak physics is examined. We assume that at low energies the degrees of freedom are those of the standard model with minimal particle content (i.e., three generations of quarks and leptons and one Higgs doublet), and that the new physics is very weakly coupled to the quarks and leptons. With these assumptions a general operator analysis reveals that the new physics leaves a characteristic signature in the pattern of corrections to the standard models contribution to precision electroweak measurements.

Leading mass corrections to the heavy quark effective theory

Abstract In dimensional regularization, any four-fermion operator mixes with an infinite number of other four-fermion operators. All but a finite number of these formally vanish when the number of space-time dimensions, d, is taken to be d=4. It is not obvious that the matrix elements of these so-called “evanescent” operators vanish beyond tree level. We show that one can choose a renormalization scheme such that this is indeed the case. Nevertheless, there are physical effects produced by these operators.