750 research outputs found
Reconstructing Generalized Exponential Laws by Self-Similar Exponential Approximants
We apply the technique of self-similar exponential approximants based on
successive truncations of continued exponentials to reconstruct functional laws
of the quasi-exponential class from the knowledge of only a few terms of their
power series. Comparison with the standard Pad\'e approximants shows that, in
general, the self-similar exponential approximants provide significantly better
reconstructions.Comment: Revtex file, 21 pages, 21 figure
P04-50 LB. Prevalence of cross-reactive HIV-1 neutralizing activity in HIV-1 infected patients with rapid or slow disease progression
P04-49 LB. Adaptation of HIV-1 envelope glycoprotein to humoral immunity at a population level
Effective action for Einstein-Maxwell theory at order RF**4
We use a recently derived integral representation of the one-loop effective
action in Einstein-Maxwell theory for an explicit calculation of the part of
the effective action containing the information on the low energy limit of the
five-point amplitudes involving one graviton, four photons and either a scalar
or spinor loop. All available identities are used to get the result into a
relatively compact form.Comment: 13 pages, no figure
Inhibition decorrelates visual feature representations in the inner retina
The retina extracts visual features for transmission to the brain. Different types of bipolar cell split the photoreceptor input into parallel channels and provide the excitatory drive for downstream visual circuits. Mouse bipolar cell types have been described at great anatomical and genetic detail, but a similarly deep understanding of their functional diversity is lacking. Here, by imaging light-driven glutamate release from more than 13,000 bipolar cell axon terminals in the intact retina, we show that bipolar cell functional diversity is generated by the interplay of dendritic excitatory inputs and axonal inhibitory inputs. The resulting centre and surround components of bipolar cell receptive fields interact to decorrelate bipolar cell output in the spatial and temporal domains. Our findings highlight the importance of inhibitory circuits in generating functionally diverse excitatory pathways and suggest that decorrelation of parallel visual pathways begins as early as the second synapse of the mouse visual system
Two-loop amplitudes with nested sums: Fermionic contributions to e+ e- --> q qbar g
We present the calculation of the nf-contributions to the two-loop amplitude
for e+ e- --> q qbar g and give results for the full one-loop amplitude to
order eps^2 in the dimensional regularization parameter. Our results agree with
those recently obtained by Garland et al.. The calculation makes extensive use
of an efficient method based on nested sums to calculate two-loop integrals
with arbitrary powers of the propagators. The use of nested sums leads in a
natural way to multiple polylogarithms with simple arguments, which allow a
straightforward analytic continuation.Comment: 31 pages, a file "coefficients.h" with the results in FORM format is
include
Single-valued harmonic polylogarithms and the multi-Regge limit
We argue that the natural functions for describing the multi-Regge limit of
six-gluon scattering in planar N=4 super Yang-Mills theory are the
single-valued harmonic polylogarithmic functions introduced by Brown. These
functions depend on a single complex variable and its conjugate, (w,w*). Using
these functions, and formulas due to Fadin, Lipatov and Prygarin, we determine
the six-gluon MHV remainder function in the leading-logarithmic approximation
(LLA) in this limit through ten loops, and the next-to-LLA (NLLA) terms through
nine loops. In separate work, we have determined the symbol of the four-loop
remainder function for general kinematics, up to 113 constants. Taking its
multi-Regge limit and matching to our four-loop LLA and NLLA results, we fix
all but one of the constants that survive in this limit. The multi-Regge limit
factorizes in the variables (\nu,n) which are related to (w,w*) by a
Fourier-Mellin transform. We can transform the single-valued harmonic
polylogarithms to functions of (\nu,n) that incorporate harmonic sums,
systematically through transcendental weight six. Combining this information
with the four-loop results, we determine the eigenvalues of the BFKL kernel in
the adjoint representation to NNLLA accuracy, and the MHV product of impact
factors to NNNLLA accuracy, up to constants representing beyond-the-symbol
terms and the one symbol-level constant. Remarkably, only derivatives of the
polygamma function enter these results. Finally, the LLA approximation to the
six-gluon NMHV amplitude is evaluated through ten loops.Comment: 71 pages, 2 figures, plus 10 ancillary files containing analytic
expressions in Mathematica format. V2: Typos corrected and references added.
V3: Typos corrected; assumption about single-Reggeon exchange made explici
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