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Ira Z. Rothstein

Publications and source records attributed to Ira Z. Rothstein.

86 records · Page 5Linked to original sources
arXiv2003

Quantum Stabilization of Compactified AdS_5

We investigate the role of quantum fluctuations in the system composed of two branes bounding a region of AdS. It is shown that the modulus effective potential generated by quantum fluctuations of both brane and bulk fields is incapable of stabilizing the space naturally at the separation needed to generate the hierarchy. Consequently, a classical stabilization mechanism is required. We describe the proper method of regulating the loop integrals and show that, for large brane separation, the quantum effects are power suppressed and therefore have negligible affects on the bulk dynamics once a classical stabilization mechanism is in place.

hep-th↗
arXiv2002

High Energy Field Theory in Truncated AdS Backgrounds

In this letter we show that, in five-dimensional anti-deSitter space (AdS) truncated by boundary branes, effective field theory techniques are reliable at high energy (much higher than the scale suggested by the Kaluza-Klein mass gap), provided one computes suitable observables. We argue that in the model of Randall and Sundrum for generating the weak scale from the AdS warp factor, the high energy behavior of gauge fields can be calculated in a {\em cutoff independent manner}, provided one restricts Green's functions to external points on the Planck brane. Using the AdS/CFT correspondence, we calculate the one-loop correction to the Planck brane gauge propagator due to charged bulk fields. These effects give rise to non-universal logarithmic energy dependence for a range of scales above the Kaluza-Klein gap.

hep-th↗
arXiv2002

Hard Scattering Factorization from Effective Field Theory

In this paper we show how gauge symmetries in an effective theory can be used to simplify proofs of factorization formulae in highly energetic hadronic processes. We use the soft-collinear effective theory, generalized to deal with back-to-back jets of collinear particles. Our proofs do not depend on the choice of a particular gauge, and the formalism is applicable to both exclusive and inclusive factorization. As examples we treat the pi-gamma form factor (gamma gamma* -> pi^0), light meson form factors (gamma* M -> M), as well as deep inelastic scattering (e- p -> e- X), Drell-Yan (p pbar -> X l+ l-), and deeply virtual Compton scattering (gamma* p -> gamma(*) p).

hep-ph↗
arXiv2001

Extracting V_{ub} Using the Radiative Decay Data

In this talk I review recent progress made in extracting V_{ub} from the cut electron energy and hadronic mass spectra of inclusive B meson decays utilizing the data from radiative decays. It is shown that an extraction is possible without modeling the B meson structure function. I discuss the issues involving the assumptions of local duality in various extractions. I also comment on the recent CLEO extraction of V_{ub}.

hep-ph↗
arXiv1999

NRQCD: A Critical Review

In this talk I review some recent applications of NRQCD. I first discuss the unquenched NRQCD lattice extractions of the strong coupling constant, paying particular attention to the recent advances in reducing systematic errors. I then discuss the progress made in testing the NRQCD/factorization formalism for onium production. In particular, I gather the evidence, or lack thereof, for the universality of the production matrix elements. I also discuss the interesting question of polarized production, which is a crucial test of the formalism. I address the viability of this theory for the J/psi system as well as what needs to be done before we can reach any definitive conclusions.

hep-ph↗
arXiv1999

A Method For Extracting cosα

We show that it is possible to extract the weak mixing angle alpha via a measurement of the rate for B^+(-) -> π^+(-) e^+e^-. The sensitivity to cos(alpha) results from the interference between the long and short distance contributions. The short distance contribution can be computed, using heavy quark symmetry, in terms of semi-leptonic form factors. More importantly, we show that, using Ward identities and a short distance operator product expansion, the long distance contribution can be calculated without recourse to light cone wave functions when the invariant mass of the lepton pair, q^2, is much larger than LQCDs. We find that for q^2 > 2 GeV^2 the branching fraction is approximately 1 * 10^{-8}|V_{td}/0.008|^2. The shape of the differential rate is very sensitive to the value of cos(alpha) at small values of q^2 with dGamma /dq^2 varying up to 50% in the interval -1< cos(alpha)< 1 at q^2= 2 GeV^2. The size of the variation depends upon the ratio V_{ub}/V_{td}.

hep-ph↗
arXiv1999

Renormalization group scaling in nonrelativistic QCD

We discuss the matching conditions and renormalization group evolution of non-relativistic QCD. A variant of the conventional MS-bar scheme is proposed in which a subtraction velocity nu is used rather than a subtraction scale mu. We derive a novel renormalization group equation in velocity space which can be used to sum logarithms of v in the effective theory. We apply our method to several examples. In particular we show that our formulation correctly reproduces the two-loop anomalous dimension of the heavy quark production current near threshold.

hep-ph↗
arXiv1998

J/psi Production at LEP: Revisited and Resummed

We present the leading order differential and total rates for J/ψproduction at LEP. By leading order we mean all terms of the form alpha_s[alpha_s log(M_Z^2/M_{psi}^2)]^n and alpha_s^{n+1} log^l(z^2) log^m(M_Z^2/M_{psi}^2), (l+m=2n-1), in the regions z=2E_psi/M_Z ~ O(1) and z << 1, respectively. In the intermediate region we interpolate using the available data. This resummation eliminates the O[alpha_s(M_psi)/alpha_s(M_Z)]~ 2 theoretical uncertainties in previous calculations. The log(z) resummation results in a suppression of the small z region due to coherent gluon emission. Comparing the zeroth moment with the LEP data we find the value for the effective octet matrix element to be <\hat O_8^ψ(^3S_1)>=0.019 GeV^3. The theoretical uncertainties are substantially smaller than those from Tevatron extractions. Using this value of the octet matrix element we make a prediction for the first moment of the differential rate and find that the resummed differential decay rate is in much better agreement with preliminary data than the color singlet result or the unresummed color octet prediction.

hep-ph↗
arXiv1997

Effective Field Theory and Matching in Non-Relativistic Gauge Theories

The effective Lagrangian and power counting rules for non-relativistic gauge theories are derived via an expansion in $1/c$. It is shown that the $1/c$ expansion leads to an effective field theory which incorporates a multipole expansion. Failure to use this expansion in the low energy theory leads to a loss of predictive power as the matching procedure becomes intractable. It is emphasized that there is not a one-to-one correspondence between operators in the modified low energy theory and those in the heavy quark effective theory.We also discuss the Lamb shift as a pedagogical example of the power counting scheme.

hep-ph↗
arXiv1997

The Octet Structure Function and Radiative Quarkonia Decay

The Operator Product Expansion, in conjunction with the power counting of non-relativistic field theory, is used to examine the end-point region of the radiative decay of heavy quark bound states with $^3S_1$ quantum numbers, $Q\bar{Q}\rightarrow γ+X$. We identify an infinite class of operators that determine the shape of the photonic end-point spectrum. These operators can be resummed to form an octet structure function which parameterizes the energy of the dynamical gluon content of the leading octet Fock state component of the quarkonium. This color-octet contribution is important when the photon spectrum is examined with a resolution given by $ΔE_γ\sim m_Qv^2$, where $v^2$ is the relative quark velocity squared. The formalism used makes explicit the shift of the end-point from its partonic to its hadronic value.

hep-ph↗
arXiv1996

Corrections to the Bjorken and Voloshin sum rules

We calculate near zero recoil the order $α_s$ corrections to the Bjorken and Voloshin sum rules that bound the $B\to D^{(*)}\ell\barν$ form factors. These bounds are derived by relating the result of inserting a complete set of physical states in a time ordered product of weak currents to the operator product expansion. The sum rules sum over physical states with excitation energies less than a scale $Δ$. We find that the corrections to the Bjorken bound are moderate, while the Voloshin bound receives sizable corrections enhanced by $Δ/Λ_{QCD}$. With some assumptions, we find that the slope parameter for the form factor $h_{A_1}$ in $B\to D^*\ell\barν$ decay satisfies $0.4\lesssimρ_{A_1}^2 \lesssim 1.3$.

hep-ph↗
arXiv1996

Hadro-Production of Quarkonia in Fixed Target Experiments

In this talk I review the recent progress made in the calculations of quarkonia production in fixed target experiments. NRQCD organizes the calculations in a systematic expansion in $α_s$ and $v$, the relative velocity between the heavy quarks. Within this formalism there are octet contributions which are not included in the color singlet model. These contributions depend upon unknown matrix elementsof local operators which are fit to the data. Using these fits, there are several predictions which do indeed improve agreement with the data. However, the prediction for the polarization of the produced states as well as the ratio of the $χ_1$ to $χ_2$ cross sections differ substantially from the data for the case of pion beams. Possible large corrections from higher twist effects are discussed as is the issue of the the proper choice of masses.

hep-ph↗
arXiv1996

Bounding Heavy Meson Form Factors Using Inclusive Sum Rules

We utilize inclusive sum rules to construct both upper and lower bounds on the form factors for B to D, D*, rho, pi, omega, K and K* semi-leptonic and radiative decays. We include the leading nonperturbative 1/E corrections and point out cases when alpha_s corrections are equally important. We compute the alpha_s correction to the lower bound on the B to D* form factor f(w) at zero recoil, thereby constraining its normalization f(1) to within 6-8% of the upper bound. We show that the B to rho form factor a_+ is suppressed at small momentum transfer by either a factor of 1/E or alpha_s. These bounds can be used to rule out phenomenological models as well as to determine values for the CKM matrix elements once radiative corrections are included.

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