6,589 research outputs found
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 CEOs
We study the relation between corporate governance and opportunistic timing of CEO option grants via backdating or otherwise. Our methodology focuses on how grant date prices rank within the price distribution of the grant month. During 1996-2005, about 12% of firms provided one or more lucky grant -- defined as grants given at the lowest price of the month -- due to opportunistic timing. Lucky grants were more likely when the board did not have a majority of independent directors and/or the CEO had longer tenure -- factors associated with increased influence of the CEO on pay-setting. We find no evidence that gains from manipulated grants served as a substitute for compensation paid through other sources; total reported compensation from such sources was higher in firms providing lucky grants. Finally, opportunistic timing has been widespread throughout the economy, with a significant presence in each of the economy's twelve (Fama-French) industries.
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
Comment on `Note on X(3872) production at hadron colliders and its molecular structure'
We briefly comment on the paper by Albaladejo et al. [arXiv:1709.09101],
rejecting its conclusions.Comment: This paper was prepared at the request of a journal editor. 3 Pages,
no figure
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