17,087 research outputs found
Constraining New Physics with D meson decays
Latest Lattice results on form factors evaluation from first principles
show that the standard model (SM) branching ratios prediction for the leptonic
decays and the semileptonic SM branching ratios of the
and meson decays are in good agreement with the world average
experimental measurements. It is possible to disprove New Physics hypothesis or
find bounds over several models beyond the SM. Using the observed leptonic and
semileptonic branching ratios for the D meson decays, we performed a combined
analysis to constrain non standard interactions which mediate the transition. This is done either by a model independent way through
the corresponding Wilson coefficients or in a model dependent way by finding
the respective bounds over the relevant parameters for some models beyond the
standard model. In particular, we obtain bounds for the Two Higgs Doublet Model
Type-II and Type III, the Left-Right model, the Minimal Supersymmetric Standard
Model with explicit R-Parity violation and Leptoquarks. Finally, we estimate
the transverse polarization of the lepton in the decay and we found it
can be as high as .Comment: 28 pages, 8 figures, 3 tables. Improved and extended analysis with
updated form factors from Lattice QC
The incidence of graft on developing-country firms
This paper measures the extent to which firms in developing countries are the target of bribes. Using new firm-level survey data from 33 African and Latin American countries, we first show that perceptions adjust slowly tofirms'experience with corrupt officials and hence are an imperfect proxy for the true incidence of graft. We then construct an experience-based index that reflects the probability that a firm will be asked for a bribe in order to complete a specified set of business transactions. On average, African firms are three times as likely to be asked for bribes as are firms in Latin America, although there is substantial variation within each region. Last, we show that graft appears to be more prevalent in countries with excessive regulation and where democracy is weak. In particular, our results suggest that the incidence of graft in Africa would fall by approximately 85 percent if countries in the region had levels of democracy and regulation similar to those that exist in Latin America.Public Sector Corruption&Anticorruption Measures,Corruption&Anitcorruption Law,Crime and Society,E-Business,Access to Finance
The Berry-Tabor conjecture for spin chains of Haldane-Shastry type
According to a long-standing conjecture of Berry and Tabor, the distribution
of the spacings between consecutive levels of a "generic'' integrable model
should follow Poisson's law. In contrast, the spacings distribution of chaotic
systems typically follows Wigner's law. An important exception to the
Berry-Tabor conjecture is the integrable spin chain with long-range
interactions introduced by Haldane and Shastry in 1988, whose spacings
distribution is neither Poissonian nor of Wigner's type. In this letter we
argue that the cumulative spacings distribution of this chain should follow the
"square root of a logarithm'' law recently proposed by us as a characteristic
feature of all spin chains of Haldane-Shastry type. We also show in detail that
the latter law is valid for the rational counterpart of the Haldane-Shastry
chain introduced by Polychronakos.Comment: LaTeX with revtex4, 6 pages, 6 figure
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