Effective Field Theory for Neutron-Deuteron Scattering: Higher Partial Waves

The phase shifts for the higher partial waves in the spin quartet and doublet channel of nd scattering are presented at next-to-leading and next-to-next-to-leading order in an effective field theory in which pions are integrated out. The results agree with both phase shift analyses and potential model calculations.Comment: 2 LaTeX2 pages with 8 eps figures, uses sprocl.sty (included), graphicx and epsfig. Abstract of a talk held at the Workshop "Chiral Dynamics 2000: Theory and Experiment," TJNAF (Newport News, USA), July 17-22, 2000; to be published in the Proceeding

Encoding and processing of sensory information in neuronal spike trains

Recently, a statistical signal-processing technique has allowed the information carried by single spike trains of sensory neurons on time-varying stimuli to be characterized quantitatively in a variety of preparations. In weakly electric fish, its application to first-order sensory neurons encoding electric field amplitude (P-receptor afferents) showed that they convey accurate information on temporal modulations in a behaviorally relevant frequency range (<80 Hz). At the next stage of the electrosensory pathway (the electrosensory lateral line lobe, ELL), the information sampled by first-order neurons is used to extract upstrokes and downstrokes in the amplitude modulation waveform. By using signal-detection techniques, we determined that these temporal features are explicitly represented by short spike bursts of second-order neurons (ELL pyramidal cells). Our results suggest that the biophysical mechanism underlying this computation is of dendritic origin. We also investigated the accuracy with which upstrokes and downstrokes are encoded across two of the three somatotopic body maps of the ELL (centromedial and lateral). Pyramidal cells of the centromedial map, in particular I-cells, encode up- and downstrokes more reliably than those of the lateral map. This result correlates well with the significance of these temporal features for a particular behavior (the jamming avoidance response) as assessed by lesion experiments of the centromedial map

The mass insertion approximation without squark degeneracy

We study the applicability of the mass insertion approximation (MIA) for calculations of neutral meson mixing when squark masses are not degenerate and, in particular, in models of alignment. We show that the MIA can give results that are much better than an order of magnitude estimate as long as the masses are not strongly hierarchical. We argue that, in an effective two-squark framework, m_q=(m_1+m_2)/2 is the best choice for the MIA expansion point, rather than, for example, m_q^2=(m_1^2+m_2^2)/2.Comment: 7 pages, revtex

K-L-\u3epi(0)gamma e(+)e(-) and its relation to CP and chiral tests

The decay KL→π0γe+e- occurs at a higher rate than the nonradiative process KL→π0e+e-, and hence can be a background to CP violation studies using the latter reaction. It also has interest in its own right in the context of chiral perturbation theory, through its relation to the decay KL→π0γγ. The leading order chiral loop contribution to KL→π0γe+e-, including the (qe++qe-)2/mπ2 dependence, is completely calculable. We present this result and also include the higher order modifications which are required in the analysis of KL→π0γγ

Direct CP Violation in B->phi K_s and New Physics

In the presence of large New Physics contributions to loop-induced b->s transitions, sizable direct CP violation in B-> phi K decays is expected on general grounds. We compute explicitly CP-violating effects using QCD factorization and find that, even in the restricted case in which New Physics has the same penguin structure as the Standard Model, the rate asymmetry can be of order one. We briefly discuss a more general scenario and comment on the inclusion of power-suppressed corrections to factorization.Comment: 3 page

A possible supersymmetric solution to the discrepancy between B -> \phi K_S and B -> \eta' K_S CP asymmetries

We present a possible supersymmetric solution to the discrepancy between the observed mixing CP asymmetries in B -> \phi K_S and B -> \eta' K_S. We show that due to the different parity in the final states of these processes, their supersymmetric contributions from the R-sector have an opposite sign, which naturally explain the large deviation between S_{\phi K_S} and S_{\eta' K_S}. We also consider the proposed mechanisms to solve the puzzle of the observed large branching ratio of B -> \eta' K and study their impact on S_{eta' K_S}.Comment: 4 pages, 2 figure