SU(3) Decay Amplitudes of Pentaquarks into Decuplet Baryons

Evidence for the existence of exotic, pentaquark baryons was first found in the invariant mass spectrum of a baryon-meson pair, with the baryon in the octet of flavor SU(3). Exotic pentaquarks may also decay into members of the spin-3/2 baryon decuplet. We calculate relations between decay rates of the exotic pentaquark into a baryon decuplet and an octet of pseudoscalar mesons based on SU(3) flavor symmetry, including the leading flavor symmetry breaking term. We consider all possible representations for an exotic pentaquark, namely, that it belongs to either a \bar{10}, 27, or 35 representation of flavor SU(3). In addition, we use the approximate SU(6) spin-flavor symmetry of baryons to derive relations between the reduced matrix elements of our calculation and those of an existing analogous calculation for decays into the baryon octet. By comparing several decay rates of exotics into both octet and decuplet baryons, our results could be used to elucidate the SU(3) nature of pentaquarks.Comment: 22 pages, no figures, a grammatical mistake has been correcte

Lucky Directors

While prior empirical work and much public attention have focused on the opportunistic timing of executives' grants, we provide in this paper evidence that outside directors' option grants have also been favorably timed to an extent that cannot be fully explained by sheer luck. Examining events in which public firms granted options to outside directors during 1996-2005, we find that 9% were "lucky grant events" falling on days with a stock price equal to a monthly low. We estimate that about 800 lucky grant events owed their status to opportunistic timing, and that about 460 firms and 1400 outside directors were associated with grant events produced by such timing. There is evidence that the opportunistic timing of director grant events has been to a substantial extent the product of backdating and not merely spring-loading based on private information. We find that directors' luck has been correlated with executives' luck. Furthermore, grant events were more likely to be lucky when the firm had more entrenching provisions protecting insiders from the risk of removal, as well as when the board did not have a majority of independent directors.

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.Comment: 7 pages, LaTe

Exclusive rare B -> K*e+e- decays at low recoil: controlling the long-distance effects

We present a model-independent description of the exclusive rare decays B-> K* e+e- in the low recoil region (large lepton invariant mass q^2 ~ m_b^2). In this region the long-distance effects from quark loops can be computed with the help of an operator product expansion in 1/Q, with Q={m_b, \sqrt{q^2}}. Nonperturbative effects up to and including terms suppressed by Lambda/Q and mc^2/mb^2 relative to the short-distance amplitude can be included in a model-independent way. Based on these results, we propose an improved method for determining the CKM matrix element |V{ub}| from a combination of rare and semileptonic B and D decays near the zero recoil point. The residual theoretical uncertainty from long distance effects in this |V{ub}| determination comes from terms in the OPE of order alpha_s(Q)\Lambda/mb, alpha_s^2(Q), mc^4/mb^4$ and duality violations and is estimated to be below 10%.Comment: 21 pages RevTex, 2 figures; v3: extensive numerical changes in the NLL analysis, with improved stability under scale dependence. Typos fixed, version to appear in Phys.Rev.

Factorization in exclusive semileptonic radiative B decays

We derive a new factorization relation for the semileptonic radiative decay B -> \pi \ell \nu \gamma in the kinematical region of a slow pion p_\pi ~ \Lambda and an energetic photon E_\gamma >> \Lambda, working at leading order in \Lambda/m_b. In the limit of a soft pion, the nonperturbative matrix element appearing in this relation can be computed using chiral perturbation theory. We present a phenomenological study of this decay, which may be important for a precise determination of the exclusive nonradiative decay.Comment: 10 pages, 3 figures; minor corrections, one reference adde