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Benjamin Grinstein

Publications and source records attributed to Benjamin Grinstein.

At least 73 records · Page 4Linked to original sources
arXiv2007

Light scalar at LHC: the Higgs or the dilaton?

It is likely that the LHC will observe a color- and charge-neutral scalar whose decays are consistent with those of the Standard Model (SM) Higgs boson. The Higgs interpretation of such a discovery is not the only possibility. For example, electroweak symmetry breaking (EWSB) could be triggered by a spontaneously broken, nearly conformal sector. The spectrum of states at the electroweak scale would then contain a narrow scalar resonance, the pseudo-Goldstone boson of conformal symmetry breaking, with Higgs-like properties. If the conformal sector is strongly coupled, this pseudo-dilaton may be the only new state accessible at high energy colliders. We discuss the prospects for distinguishing this mode from a minimal Higgs boson at the LHC and ILC. The main discriminants between the two scenarios are (1) cubic self-interactions and (2) a potential enhancement of couplings to massless SM gauge bosons. A particularly interesting situation arises when the scale f of conformal symmetry breaking is approximately the electroweak scale v~246 GeV. Although in this case the LHC may not be able to tell apart a pseudo-dilaton from the Higgs boson, the self-interactions differ in a way that depends only on the scaling dimension of certain operators in the conformal sector. This opens the possibility of using dilaton pair production at future colliders as a probe of EWSB induced by nearly conformal new physics.

hep-ph↗
arXiv2007

The Lee-Wick Standard Model

We construct a modification of the standard model which stabilizes the Higgs mass against quadratically divergent radiative corrections, using ideas originally discussed by Lee and Wick in the context of a finite theory of quantum electrodynamics. The Lagrangian includes new higher derivative operators. We show that the higher derivative terms can be eliminated by introducing a set of auxiliary fields; this allows for convenient computation and makes the physical interpretation more transparent. Although the theory is unitary, it does not satisfy the usual analyticity conditions.

hep-ph↗
arXiv2007

FPCP Theory Overview

We first review some aspects of the determination of the sides and angles of the unitarity triangle. We pay particular attention to theory shortcomings, and present many alternative proposals for the determination of |Vub| (which at present is problematic). We then turn our attention to the more general question: What have we learned so far about flavor physics and where do we go from here? We argue that the aim of Flavor Physics should be to establish or rule out Minimal Flavor Violating interactions up to a scale of 10 TeV.

hep-ph↗
arXiv2007

Overview: Sides of the Unitarity Triangle

This is an opening talk for the workshop and is intended to be provocative. We take a stab at the following questions: How well do we really know the sides of the unitarity triangle? What else could we do to improve? (I propose several new measurements). What precision should we ultimately aim at in the determination of CKM elements? What have we learned so far about flavor physics? Where do we go from here?

hep-ph↗
arXiv2007

Minimal Flavor Violation

If new physics is called upon to explain away fine tunings, like the hierarchy problem, then, we argue, the principle of Minimal Flavor Violation is inescapable. We review the principle and recent extensions to the lepton sector and to Grand-Unified theories.

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arXiv2007

Neutrino Masses in the Lee-Wick Standard Model

Recently, an extension of the standard model based on ideas of Lee and Wick has been discussed. This theory is free of quadratic divergences and hence has a Higgs mass that is stable against radiative corrections. Here, we address the question of whether or not it is possible to couple very heavy particles, with masses much greater than the weak scale, to the Lee-Wick standard model degrees of freedom and still preserve the stability of the weak scale. We show that in the LW-standard model the familiar see-saw mechanism for generating neutrino masses preserves the solution to the hierarchy puzzle provided by the higher derivative terms. The very heavy right handed neutrinos do not destabilize the Higgs mass. We give an example of new heavy degrees of freedom that would destabilize the hierarchy, and discuss a general mechanism for coupling other heavy degrees of freedom to the Higgs doublet while preserving the hierarchy.

hep-ph↗
arXiv2006

Falsifying Models of New Physics Via WW Scattering

We show that the coefficients of operators in the electroweak chiral Lagrangian can be bounded if the underlying theory obeys the usual assumptions of Lorentz invariance, analyticity, unitarity and crossing to arbitrarily short distances. Violations of these bounds can be explained by either the existence of new physics below the naive cut-off of the the effective theory, or by the breakdown of one of these assumptions in the short distance theory. As a corollary, if no light resonances are found, then a measured violation of the bound would falsify generic models of string theory.

hep-ph↗
arXiv2006

Grand Unification and the Principle of Minimal Flavor Violation

Minimal Flavor Violation is an attractive approach to suppress unacceptably large flavor changing neutral currents from beyond the standard model physics at the TeV scale. It can be used in theories with low energy supersymmetry, multi Higgs doublet theories and other extensions of the minimal standard model. We show how minimal flavor violation can be implemented in Grand Unified theories.

hep-ph↗
arXiv2006

Shape and soft functions of HQET and SCET in the 't Hooft Model

The main application of Heavy Quark Effective Theory (HQET) and of Soft Collinear Effective Theory (SCET) is in establishing factorization theorems for exclusive and semi-inclusive decays of heavy mesons. However, the calculation of the soft factors from the HQET or SCET factorization relations is, as usual, impeded by the non-perturbative aspect of the strong interactions. In the hope of gaining some insights into some of these quantities we compute them in the 't Hooft model. We find that the B-meson shape function is exactly given by the square of the B-meson light-cone wave-function. The structure of the B-pi structure function is more complicated: it is given by the product of wave-functions or by a resonant sum depending on the kinematics. The result simplifies dramatically in the chiral limit, where it can be compared with general arguments based on Heavy Meson-Chiral Perturbation theory. No attempt is made to use these results for applications to phenomenology.

hep-ph↗
arXiv2006

Factorization in B -> K pi e+e- decays

We derive factorization relations for the transverse helicity amplitudes in the rare decays B-> Kπl+l- at leading order in Lambda/m_b, in the kinematical region with an energetic kaon and a soft pion. We identify and compute a new contribution of leading order in Lambda/m_b to the B->Kπl+l- amplitude, which is not present in the one-body decay B-> K*l+l-. As an application we study the forward-backward asymmetry (FBA) of the lepton momentum angular distribution in B-> Kπl+l- decays away from the K* resonance. The FBA in these decays has a zero at q0^2 = q0^2(M_{Kpi}), which can be used, in principle, for determining the Wilson coefficients C_{7,9} and testing the Standard Model. We point out that the slope of the q0^2(M_{Kpi}^2) curve contains the same information about the Wilson coefficients as the location of the zero, but is less sensitive to unknown nonperturbative dynamics. We estimate the location of the zero at leading order in factorization, and using a resonant model for the B -> Kπl+l- nonfactorizable amplitude.

hep-ph↗
arXiv2006

Phenomenology of Minimal Lepton Flavor Violation

We extend the effective theory of Minimal Lepton Flavor Violation (MLFV) by including four-lepton operators. We compute the rates for mu -> 3 e and tau -> 3 ell decays and point out several new ways to test the hypothesis of MLFV. We also investigate to what extent it will be possible from (future) experimental information to pin down the contributions of different effective operators. In particular we look for experimental handles on quark-lepton operators of the type $\bar{ell}_i Γ\ell_j \times \bar q Γq$ by working out their contribution to hadronic processes such as tau -> mu pi^0, pi^0 -> mu^- e^+, Y -> tau^- mu^+, as well as to purely leptonic decays such as mu -> 3 e through loop effects.

hep-ph↗
arXiv2006

The CP asymmetry in B^0(t) -> K_S π^0 γin the Standard Model

The time-dependent CP asymmetry in exclusive B^0(t) -> K^{*0}γdecays has been proposed as a probe of new physics in B decays. Recently, this method was extended to radiative decays into multibody hadronic final states such as B^0(t)-> K_Sπ^0γand B^0(t)-> π^+π^-γ. The CP asymmetry in these decays vanishes to the extent that the photon is completely polarized. In the Standard Model, the photon emitted in b-> sγhas high left-handed polarization, but right-handed contamination enters already at leading order in Λ/m_b even for vanishing light quark masses. We compute here the magnitude of this effect and the time dependent CP asymmetry parameter S_{K_S π^0γ}. We find that the Standard Model can easily accomodate values of S as large as 10%, but a precise value cannot be obtained at present because of strong interactions uncertainties.

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arXiv2005

Flavor Changing Supersymmetry Interactions in a Supernova

We consider for the first time R-parity violating interactions of the Minimal Standard Supersymmetric Model involving neutrinos and quarks (``flavor changing neutral currents'', FCNC's) in the infall stage of stellar collapse. Our considerations extend to other kinds of flavor changing neutrino reactions as well. We examine non-forward neutrino scattering processes on heavy nuclei and free nucleons in the supernova core. This investigation has led to four principal original discoveries/products: (1) first calculation of neutrino flavor changing cross sections for spin one half (e.g. free nucleon) and spin zero nuclear targets; (2) discovery of nuclear mass number squared (A squared) coherent amplification of neutrino-quark FCNC's; (3) analysis of FCNC-induced alteration of electron capture and weak/nuclear equilibrium in the collapsing core; and (4) generalization of the calculated cross sections (mentioned in 1) for the case of hot heavy nuclei to be used in collapse/supernova and neutrino transport simulations. The scattering processes that we consider allow electron neutrinos to change flavor during core collapse, thereby opening holes in the electron neutrino sea, which allows electron capture to proceed and results in a lower core electron fraction. A lower electron fraction implies a lower homologous core mass, a lower shock energy, and a greater nuclear photo-disintegration burden for the shock. In addition, unlike the standard supernova model, the core now could have net muon and/or tau lepton numbers. These effects could be significant even for supersymmetric couplings below current experimental bounds.

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arXiv2005

Minimal Flavor Violation in the Lepton Sector

We extend the notion of Minimal Flavor Violation to the lepton sector. We introduce a symmetry principle which allows us to express lepton flavor violation in the charged lepton sector in terms of neutrino masses and mixing angles. We explore the dependence of the rates for flavor changing radiative charged lepton decays (ell(i) -> ell(j) + gamma) and mu-to-e conversion in nuclei on the scales for total lepton number violation, lepton flavor violation and the neutrino masses and mixing angles. Measurable rates are obtained when the scale for total lepton number violation is much larger than the scale for lepton flavor violation.

hep-ph↗
arXiv2005

Chiral symmetry and exclusive B decays in the SCET

We describe a chiral formalism for processes involving both energetic hadrons and soft Goldstone bosons, which extends the application of soft-collinear effective theory to multibody B decays. The nonfactorizable helicity amplitudes for heavy meson decays into multibody final states satisfy symmetry relations analogous to the large energy form factor relations, which are broken at leading order in Lambda/mb by calculable factorizable terms. We use the chiral effective theory to compute the leading corrections to these symmetry relations in B -> M_n pi ell\barνand B -> M_n pi e+e- decays.

hep-ph↗
arXiv2005

Heavy Meson Physics: What have we learned in Twenty Years?

I give a personal account of the development of the field of heavy quarks. After reviewing the experimental discovery of charm and bottom quarks, I describe how the field's focus shifted towards determination of CKM elements and how this has matured into a precision science.

hep-ph↗
arXiv2004

CKM Sides: Theory

We review the theory of the determination of the CKM elements Vcb and Vub. Particular attention is paid to the determination of Vcb through inclusive semileptonic B decays to charm using a moment analysis, since this has shown most progress recently. A precise method for the determination of Vub via exclusive decays is described.

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