24,739 research outputs found
Sigma pole position and errors of a once and twice subtracted dispersive analysis of pi-pi scattering data
We show how the new precise data on kaon decays together with forward
dispersion relations, sum rules and once- and twice-subtracted
Roy's equations allow for a precise determination of the sigma meson pole
position. We present a comparison and a study of the different sources of
uncertainties when using either once- or twice-subtracted Roy's equations to
analyze the data. Finally we present a preliminary determination of the sigma
pole from the constrained dispersive data analysis.Comment: 4 pages, 6 figures. Contribution to the proceedings of the QCD08 14th
International QCD Conference. 7-12th July 2008 Montpellier (France); one
reference removed, changed errors in Eqs (4), (5) and (7
All-electron theory of the coupling between laser-induced coherent phonons in bismuth
Using first principles, all-electron calculations and dynamical simulations
we study the behavior of the A_1g and E_g coherent phonons induced in Bi by
intense laser pulses. We determine the potential landscapes in the laser heated
material and show that they exhibit phonon-softening, phonon-phonon coupling,
and anharmonicities. As a consequence the E_g mode modulates the A_1g
oscillations and higher harmonics of both modes appear, which explains recent
isotropic reflectivity measurements. Our results offer a unified description of
the different experimental observations performed so far on bismuth.Comment: 3 figure
On the spectrum of a matrix model for the D=11 supermembrane compactified on a torus with non-trivial winding
The spectrum of the Hamiltonian of the double compactified D=11 supermembrane
with non-trivial central charge or equivalently the non-commutative symplectic
super Maxwell theory is analyzed. In distinction to what occurs for the D=11
supermembrane in Minkowski target space where the bosonic potential presents
string-like spikes which render the spectrum of the supersymmetric model
continuous, we prove that the potential of the bosonic compactified membrane
with non-trivial central charge is strictly positive definite and becomes
infinity in all directions when the norm of the configuration space goes to
infinity. This ensures that the resolvent of the bosonic Hamiltonian is
compact. We find an upper bound for the asymptotic distribution of the
eigenvalues.Comment: 11 pages, LaTe
New dispersion relations in the description of scattering amplitudes
We present a set of once subtracted dispersion relations which implement
crossing symmetry conditions for the scattering amplitudes below 1
GeV. We compare and discuss the results obtained for the once and twice
subtracted dispersion relations, known as Roy's equations, for three
partial JI waves, S0, P and S2. We also show that once subtracted dispersion
relations provide a stringent test of crossing and analyticity for
partial wave amplitudes, remarkably precise in the 400 to 1.1 GeV region, where
the resulting uncertainties are significantly smaller than those coming from
standard Roy's equations, given the same input.Comment: 8 pages, 2 figures, to appear in the Proceedings of the Meson 2008
conference, June 6-10, 2008, Cracow, Polan
Quantization of Weyl invariant unimodular gravity with antisymmetric ghost fields
The enforcement of the unimodularity condition in a gravity theory by means
of a Lagrange multiplier leads, in general, to inconsistencies upon
quantization. This is so, in particular, when the classic linear splitting of
the metric between the background and quantum fields is used. To avoid the need
of introducing such a Lagrange multiplier while using the classic linear
splitting, we carry out the quantization of unimodular gravity with extra Weyl
symmetry by using Becchi-Rouet-Stora-Tyutin (BRST) techniques. Here, two gauge
symmetries are to be gauge-fixed: transverse diffeomorphisms and Weyl
transformations. We perform the gauge-fixing of the transverse diffeomorphism
invariance by using BRST transformations that involve antisymmetric ghost
fields. We show that these BRST transformations are compatible with the BRST
transformations needed to gauge-fix the Weyl symmetry, so that they can be
combined in a set of transformations generated by a single BRST operator.
Newton's law of gravitation is derived within the BRST formalism we put forward
as well as the Slavnov-Taylor equation.Comment: 24 pages, 1 table, 1 figur
Opportunities at the Intersection of Synthetic Biology, Machine Learning, and Automation
Our inability to predict the behavior of biological systems severely hampers progress in bioengineering and biomedical applications. We cannot predict the effect of genotype changes on phenotype, nor extrapolate the large-scale behavior from small-scale experiments. Machine learning techniques recently reached a new level of maturity, and are capable of providing the needed predictive power without a detailed mechanistic understanding. However, they require large amounts of data to be trained. The amount and quality of data required can only be produced through a combination of synthetic biology and automation, so as to generate a large diversity of biological systems with high reproducibility. A sustained investment in the intersection of synthetic biology, machine learning, and automation will drive forward predictive biology, and produce improved machine learning algorithms
A Bose-Einstein condensate interferometer with macroscopic arm separation
A Michelson interferometer using Bose-Einstein condensates is demonstrated
with coherence times of up to 44 ms and arm separations up to 0.18 mm. This arm
separation is larger than that observed for any previous atom interferometer.
The device uses atoms weakly confined in a magnetic guide and the atomic motion
is controlled using Bragg interactions with an off-resonant standing wave laser
beam.Comment: 4 pages, 3 figure
Nonperturbative SL(2,Z) (p,q)-strings manifestly realized on the quantum M2
The SL(2,Z) duality symmetry of IIB superstring is naturally realized on the
D=11 supermembrane restricted to have central charges arising from a nontrivial
wrapping. This supermembrane is minimally immersed on the target space (MIM2).
The hamiltonian of the MIM2 has a discrete quantum spectrum. It is manifestly
invariant under the SL(2,Z) symmetry associated to the conformal symmetry on
the base manifold and under a SL(2,Z) symmetry on the moduli of the target
space. The mass contribution of the string states on the MIM2 is obtained by
freezing the remaining degrees of freedom. It exactly agrees with the
perturbative spectrum of the (p,q) IIB and IIA superstring compactified on a
circle. We also construct a MIM2 in terms of a dual target space, then a (p,q)
set of non-perturbative states associated to the IIA superstring is obtained.Comment: 32pages, late
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