arXiv subjects

Adam F. Falk

Publications and source records attributed to Adam F. Falk.

At least 19 recordsLinked to original sources

arXiv2007

Decoupling and Destabilizing in Spontaneously Broken Supersymmetry

The supersymmetric analog of the Goldberger-Treiman relation plays a critical role in the low energy effective theory of models in which supersymmetry is spontaneously broken in a hidden sector. The interactions that connect the hidden and visible sectors break a global symmetry, which implies that the low energy theory must be constructed consistently in inverse powers of the messenger scale. The Goldberger-Treiman relation determines the couplings of the Goldstino to the visible sector fields. These couplings are fixed by the soft supersymmetry breaking terms within a power counting scheme that is stable under radiative corrections. We describe the power counting of the low energy effective theory, first for a toy model of extended technicolor and then for the supersymmetric standard model. One implication of this work for supersymmetry phenomenology is the observation that Goldstino loops can destabilize the weak scale if the low energy theory is not constructed consistently. Another is that Goldstino loops induce all visible sector operators not forbidden by symmetries. The magnitudes of these operators are determined by the consistent power counting of the low energy effective theory.

hep-ph↗

arXiv2004

The $D^0 - \bar D^0$ mass difference from a dispersion relation

We study the Standard Model prediction for the mass difference between the two neutral D meson mass eigenstates, $Δm$. We derive a dispersion relation based on heavy quark effective theory that relates $Δm$ to an integral of the width difference of heavy mesons, $ΔΓ$, over varying values of the heavy meson mass. Modeling the $m_D$-dependence of certain D decay partial widths, we investigate the effects of SU(3) breaking from phase space on the mass difference. We find that $Δm$ may be comparable in magnitude to $ΔΓ$ in the Standard Model.

hep-ph↗

arXiv2003

Comment on extracting alpha from B -> rho rho

Recent experimental results on $B\toρρ$ decays indicate that the CP asymmetry $S_{ρ^+ρ^-}$ will give an interesting determination of $α=\arg[-(V_{td}V_{tb}^*)/(V_{ud}V_{ub}^*)]$. In the limit when the $ρ$ width is neglected, the $B\toππ$ isospin analysis can also be applied to $B\toρρ$, once an angular analysis is used to separate transversity modes. The present bound on the shift of $S_{ρ^+ρ^-}$ from the true $\sin2α$ is already stronger than it is for $S_{π^+π^-}$. We point out a subtle violation of the isospin relations when the two $ρ$ mesons are observed with different invariant masses, and how to constrain this effect experimentally.

hep-ph↗

arXiv2003

Threshold effects in excited charmed baryon decays

Motivated by recent results on charmed baryons from CLEO and FOCUS, we reexamine the couplings of the orbitally excited charmed baryons. Due to its proximity to the [Sigma_c pi] threshold, the strong decays of the Lambda_c(2593) are sensitive to finite width effects. This distorts the shape of the invariant mass spectrum in Lambda_{c1}-> Lambda_c pi^+pi^- from a simple Breit-Wigner resonance, which has implications for the experimental extraction of the Lambda_c(2593) mass and couplings. We perform a fit to unpublished CLEO data which gives M(Lambda_c(2593)) - M(Lambda_c) = 305.6 +- 0.3 MeV and h2^2 = 0.24^{+0.23}_{-0.11}, with h2 the Lambda_{c1}-> Sigma_c pi strong coupling in the chiral Lagrangian. We also comment on the new orbitally excited states recently observed by CLEO.

hep-ph↗

arXiv2002

Flavor Physics and the CKM Matrix: An Overview

I review the current status of our knowledge of CP violation and flavor physics. I discuss where one should look for future improvements, and outline the experimental and theoretical priorities of the field.

hep-ph↗

arXiv2001

SU(3) Breaking and D0-D0bar Mixing

The main challenge in the Standard Model calculation of the mass and width difference in the D0-D0bar system is to estimate the size of SU(3) breaking effects. We prove that D meson mixing occurs in the Standard Model only at second order in SU(3) violation. We consider the possibility that phase space effects may be the dominant source of SU(3) breaking. We find that y=(Delta Gamma)/(2Gamma) of the order of one percent is natural in the Standard Model, potentially reducing the sensitivity to new physics of measurements of D meson mixing.

hep-ph↗

arXiv2001

CP Tagged Decays at SuperBaBar

We explore the possibility of measuring the CKM parameter gamma using CP tagged decays at a very high luminosity e+e- B Factory. A new collider capable of integrating as much as 10 inverse attobarns per year is being discussed as a possible future for SLAC beyond the current PEP-II program, and could also be in the future of KEK. In two years of operation, it could be possible for a successor to BaBar or Belle to accumulate a sample of one million CP tagged B decays. We find that a theoretically clean extraction of gamma with uncertainty less than 5 degrees may be achievable in the analysis of such a data set.

hep-ph↗

arXiv2000

Effects from the charm scale in K+ -> pi+ nu nubar

We consider contributions to the rare decay K+ -> pi+ nu nubar which become nonlocal at the charm scale. Compared to the leading term, such amplitudes are suppressed by two powers of mK/mc and could potentially give corrections at the level of 15%. We compute the leading coefficients of the subleading dimension eight operators in the effective theory below the charm mass. The matrix elements of these operators cannot all be calculated from first principles and some must be modeled. We find that these contributions are likely to be small, but the estimate is sufficiently uncertain that the result may be as large as the existing theoretical uncertainty from other sources.

hep-ph↗

arXiv2000

The CKM Matrix and the Heavy Quark Expansion

These lectures contain an elementary introduction to heavy quark symmetry and the heavy quark expansion. Applications such as the expansion of heavy meson decay constants and the treatment of inclusive and exclusive semileptonic B decays are included. The use of heavy quark methods for the extraction of |V_cb| and |V_ub| is presented is some detail.

hep-ph↗

arXiv2000

Measuring gamma cleanly with CP-tagged Bs and Bd decays

We propose a new method for measuring the CKM phase gamma using the partial rates for CP-tagged Bs decays. Such an experiment could be performed at a very high luminosity symmetric e+e- collider operating at the Upsilon(5S) resonance, where the Bs-Bsbar state is produced in a state of definite CP. We also discuss CP-tagging in the Bd system at the Upsilon(4S), where a time-dependent analysis is required to compensate for the anticipated large CP violation in Bd-Bdbar mixing.

hep-ph↗

arXiv1999

Strong phases and D0-anti-D0 mixing parameters

We argue that there could be large, SU(3) violating resonance contributions to D -> K pi decays which would affect the extraction of the D0-anti-D0 mixing parameters from experiment. Such contributions can induce a large strong phase in the interference between the doubly Cabibbo suppressed and the mixing induced Cabibbo favored contributions to the D0 -> K^+ pi^- and anti-D0 -> K^- pi^+ decays. Consequently, the interpretation of a large, CP conserving interference term can involve a large mass difference Delta M rather than a large width difference Delta Gamma.

hep-ph↗

arXiv1999

Measuring V_ub in Inclusive B Decays to Charm

We propose a novel method of measuring the CKM matrix element V_ub, via inclusive B decays to "wrong sign" charm. This process is mediated by the quark level decay b -> u cbar s'. When normalized to the inclusive semileptonic decay rate, the theoretical expression is very well behaved, with small uncertainties from unknown quark masses and no leading renormalon ambiguity. We compute the decay rate for this process, including the leading perturbative and nonperturbative corrections.

hep-ph↗

arXiv1999

B Decays, the Unitarity Triangle, and the Universe

A review is given of recent developments in the physics of flavor. Current constraints on the Cabibbo-Kobayashi-Maskawa matrix are discussed and related to the recent measurements of epsilon'/epsilon, sin(2beta) and K+ -> pi+ nu nubar. A brief review is given of the connection between CP violation in B decays and electroweak baryogenesis. Finally, there is an extensive discussion of how present and proposed experiments in K and B physics can constrain the pattern of flavor changing processes at low energies and, one hopes, eventually provide unambiguous evidence of physics beyond the Standard Model.

hep-ph↗

arXiv1999

Precision Observables and Electroweak Theories

We compute the bounds from precision observables on alternative theories of electroweak symmetry breaking. We show that a cut-off as large as 3 TeV can be accomodated by the present data, without unnatural fine tuning.

hep-ph↗

arXiv1999

Phenomenology of V_ub from Ratios of Inclusive B Decay Rates

We explore the theoretical feasibility of extracting V_ub from two ratios built from B meson inclusive partial decays, R_1 = Gamma(b-> u cbar s)/3Gamma(b -> c l nu), and R_2 = [Gamma(b -> c X) - Gamma(b -> cbar X)]/Gamma(b -> c ubar d). We discuss contributions to these quantities from perturbative and nonperturbative physics, and show that they can be computed with overall uncertainties at the level of 10%.

hep-ph↗

arXiv1999

Radiative Leptonic B_c Decays in Effective Field Theory

The recent discovery of the B_c meson by the CDF collaboration and proposed new experiments at Fermilab and CERN motivate new theoretical studies of the B_c system. Here we investigate the radiative leptonic decay B_c -> gamma l nu. This process is an important background to the annihilation process B_c -> l nu, which will be used to extract the B_c decay constant. We perform a model-independent calculation, based on QCD, of the partial width and various kinematic distributions. We also examine the decay within the framework of NRQCD, an effective field theory of nonrelativistic quarks, generalizing the NRQCD Lagrangian to include external sources for the weak and electromagnetic currents. Finally, we comment on the role of the B_c* intermediate state for very soft photon energies.

hep-ph↗

arXiv1998

Introduction to Hadronic B Physics

An overview of the theory of B physics is given, with an emphasis on issues in the strong interactions and hadronic physics. This article is taken from an introductory chapter of The BaBar Physics Book - Physics at an Asymmetric B Factory, SLAC Report SLAC-R-504. It is written at the level of a basic survey aimed at the experimental community.

hep-ph↗

arXiv1998

Final State Interactions in Hadronic B Decays

I discuss the effect of final state interactions on the determination of the CKM angle γfrom B -> K + pi decays. Using a simple Regge-based model for rescattering processes, I argue that such effects could be substantial enough to make it problematic to obtain reliable limits on γin this way. Fortunately, an analysis of B -> K + K decays may provide model-independent bounds on rescattering contributions.

hep-ph↗