501 research outputs found
Towards next-to-next-to-leading-log accuracy for the width difference in the system: fermionic contributions to order and
We calculate a class of three-loop Feynman diagrams which contribute to the
next-to-next-to-leading logarithmic approximation for the width difference
in the system. The considered diagrams
contain a closed fermion loop in a gluon propagator and constitute the order
, where is the number of light quarks. Our results entail
a considerable correction in that order, if is expressed in
terms of the pole mass of the bottom quark. If the scheme is
used instead, the correction is much smaller. As a result, we find a decrease
of the scheme dependence. Our result also indicates that the usually quoted
value of the NLO renormalization scale dependence underestimates the
perturbative error.Comment: We corrected a typographical mistake in Eq. (4.18), made larger axis
labels in Fig.2. Version accepted by JHE
Towards the NNLL precision in
The present NLL prediction for the decay rate of the rare inclusive process
has a large uncertainty due to the charm mass
renormalization scheme ambiguity. We estimate that this uncertainty will be
reduced by a factor of 2 at the NNLL level. This is a strong motivation for the
on-going NNLL calculation, which will thus significantly increase the
sensitivity of the observable to possible new degrees
of freedom beyond the SM. We also give a brief status report of the NNLL
calculation.Comment: 5 pages, 2 figures, contribution to the proceedings of EPS-HEP 200
Reduction of Charm Quark Mass Scheme Dependence in at the NNLL Level
The uncertainty of the theoretical prediction of the
branching ratio at NLL level is dominated by the charm mass renormalization
scheme ambiguity. In this paper we calculate those NNLL terms which are related
to the renormalization of , in order to get an estimate of the
corresponding uncertainty at the NNLL level. We find that these terms
significantly reduce (by typically a factor of two) the error on induced by the definition of . Taking into account the
experimental accuracy of around 10% and the future prospects of the
factories, we conclude that a NNLL calculation would increase the sensitivity
of the observable to possible new degrees of freedom
beyond the SM significantly.Comment: 13 pages including 3 figure
Characterization of sequences and mechanisms through which ISE/ISS-3 regulates FGFR2 splicing
Alternative splicing of fibroblast growth factor receptor-2 (FGFR2) mutually exclusive exons IIIb and IIIc results in highly cell-type-specific expression of functionally distinct receptors, FGFR2-IIIb and FGFR2-IIIc. We previously identified an RNA cis-element, ISE/ISS-3, that enhanced exon IIIb splicing and silenced exon IIIc splicing. Here, we have performed comprehensive mutational analysis to define critical sequence motifs within this element that independently either enhance splicing of upstream exons or repress splicing of downstream exons. Such analysis included use of a novel fluorescence-based splicing reporter assay that allowed quantitative determination of relative functional activity of ISE/ISS-3 mutants using flow cytometric analysis of live cells. We determined that specific sequences within this element that mediate splicing enhancement also mediate splicing repression, depending on their position relative to a regulated exon. Thus, factors that bind the element are likely to be coordinately involved in mediating both aspects of splicing regulation. Exon IIIc silencing is dependent upon a suboptimal branchpoint sequence containing a guanine branchpoint nucleotide. Previous studies of exon IIIc splicing in HeLa nuclear extracts demonstrated that this guanine branchsite primarily impaired the second step of splicing suggesting that ISE/ISS-3 may block exon IIIc inclusion at this step. However, results presented here that include use of newly developed in vitro splicing assays of FGFR2 using extracts from a cell line expressing FGFR2-IIIb strongly suggest that cell-type-specific silencing of exon IIIc occurs at or prior to the first step of splicing
Spectrum of surface-mode contributions to the excitation probability for electron beam interacting with sharp-edged dielectric wedges
The interaction of a nonrelativistic charged particle beam, travelling
parallel to the surface of a sharp-edged dielectric wedge is analyzed. The
general expressions for excitation probability are obtained for a beam moving
along the direction of a symmetry axis, either outside or inside the dielectric
wedge. The dielectric function of the medium is assumed to be isotropic, and
numerical results are given for the materials of experimental interest.Comment: LaTeX 2.09, 15 pages, 10 figure
- …