28,371 research outputs found
The rare decay B --> X_s l^+ l^- to NNLL precision for arbitrary dilepton invariant mass
We present a new phenomenological analysis of the inclusive rare decay . In particular, we present the first calculation of the NNLL
contributions due to the leading two-loop matrix elements, evaluated for
arbitrary dilepton invariant mass. This allows to obtain the first NNLL
estimates of the dilepton mass spectrum and the lepton forward-backward
asymmetry in the high region, and to provide an
independent check of previously published results in the low region. The numerical impact of these NNLL corrections in the
high-mass region () amounts to -13% in the
integrated rate, and leads to a reduction of the scale uncertainty to .
The impact of non-perturbative contributions in this region is also discussed
in detail.Comment: 40 pages, 12 figures. v2: extended phenomenological discussion;
results unchanged; published versio
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Two novel nonlinear companding schemes with iterative receiver to reduce PAPR in multi-carrier modulation systems
Companding transform is an efficient and simple method to reduce the Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Modulation (MCM) systems. But if the MCM signal is only simply operated by inverse companding transform at the receiver, the resultant spectrum may exhibit severe in-band and out-of-band radiation of the distortion components, and considerable peak regrowth by excessive channel noises etc. In order to prevent these problems from occurring, in this paper, two novel nonlinear companding schemes with a iterative receiver are proposed to reduce the PAPR. By transforming the amplitude or power of the original MCM signals into uniform distributed signals, the novel schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Despite moderate complexity increasing at the receiver, but it is especially suitable to be combined with iterative channel estimation. Computer simulation results show that the proposed schemes can offer good system performances without any bandwidth expansion
Neutrino emission from a GRB afterglow shock during an inner supernova shock breakout
The observations of a nearby low-luminosity gamma-ray burst (GRB) 060218
associated with supernova SN 2006aj may imply an interesting astronomical
picture where a supernova shock breakout locates behind a relativistic GRB jet.
Based on this picture, we study neutrino emission for early afterglows of GRB
060218-like GRBs, where neutrinos are expected to be produced from photopion
interactions in a GRB blast wave that propagates into a dense wind.
Relativistic protons for the interactions are accelerated by an external shock,
while target photons are basically provided by the incoming thermal emission
from the shock breakout and its inverse-Compton scattered component. Because of
a high estimated event rate of low-luminosity GRBs, we would have more
opportunities to detect afterglow neutrinos from a single nearby GRB event of
this type by IceCube. Such a possible detection could provide evidence for the
picture described above.Comment: 6 pages, 2 figures, accepted for publication in MNRA
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