50,896 research outputs found
Cluster algebras in scattering amplitudes with special 2D kinematics
We study the cluster algebra of the kinematic configuration space
of a n-particle scattering amplitude restricted to the
special 2D kinematics. We found that the n-points two loop MHV remainder
function found in special 2D kinematics depend on a selection of
\XX-coordinates that are part of a special structure of the cluster algebra
related to snake triangulations of polygons. This structure forms a necklace of
hypercubes beads in the corresponding Stasheff polytope. Furthermore in , the cluster algebra and the selection of \XX-coordinates in special 2D
kinematics replicates the cluster algebra and the selection of \XX-coordinates
of two loop MHV amplitude in 4D kinematics.Comment: 22 page
The mass function of GX 339-4 from spectroscopic observations of its donor star
We obtained 16 VLT/X-shooter observations of GX 339-4 in quiescence in the
period May - September 2016 and detected absorption lines from the donor star
in its NIR spectrum. This allows us to measure the radial velocity curve and
projected rotational velocity of the donor for the first time. We confirm the
1.76 day orbital period and we find that = km s,
km s and km s. From
these values we compute a mass function , a
factor lower than previously reported, and a mass ratio . We confirm the donor is a K-type star and estimate that it contributes
of the light in the - and H-band. We constrain the binary
inclination to and the black hole mass to
. GX 339-4 may therefore be the
first black hole to fall in the 'mass-gap' of .Comment: 11 pages, 7 figures, accepted for publication in Ap
Time-resolved photometry of the nova remnants DM Gem, CP Lac, GI Mon, V400 Per, CT Ser and XX Tau
We present the first results of a photometric survey of poorly studied nova remnants in the Northern Hemisphere.
The main results are as follows: DM Gem shows a modulation at 0.123 d (probably linked to the orbit) and rapid variations at ∼22 min. A moderate resolution spectrum taken at the time of the photometric observations shows intense He II λ4686 and Bowen emission, characteristic of an intermediate polar or a SW Sex star. Variability at 0.127 d and intense flickering (or quasi-periodic oscillations) are the main features of the light curve of CP Lac. A 0.1-mag dip lasting for ∼45 min is observed in GI Mon, which could be an eclipse. A clear modulation (probably related to the orbital motion) either at 0.179 d or 0.152 d
is observed in the B-band light curve of V400 Per. The results for CT Ser point to an orbital period close to 0.16 d. Intense flickering is also characteristic of this old nova. Finally, XX Tau shows a possible periodic signal near 0.14 d and displays fast variability at ∼24 min. Its brightness seems to be modulated at ∼5 d. We relate this long periodicity to the motion of an eccentric/tilted accretion disc in the binary
Finite size scaling of the bayesian perceptron
We study numerically the properties of the bayesian perceptron through a
gradient descent on the optimal cost function. The theoretical distribution of
stabilities is deduced. It predicts that the optimal generalizer lies close to
the boundary of the space of (error-free) solutions. The numerical simulations
are in good agreement with the theoretical distribution. The extrapolation of
the generalization error to infinite input space size agrees with the
theoretical results. Finite size corrections are negative and exhibit two
different scaling regimes, depending on the training set size. The variance of
the generalization error vanishes for confirming the
property of self-averaging.Comment: RevTeX, 7 pages, 7 figures, submitted to Phys. Rev.
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