16,751 research outputs found
Skewed Sudakov Regime, Harmonic Numbers, and Multiple Polylogarithms
On the example of massless QED we study an asymptotic of the vertex when only
one of the two virtualities of the external fermions is sent to zero. We call
this regime the skewed Sudakov regime. First, we show that the asymptotic is
described with a single form factor, for which we derive a linear evolution
equation. The linear operator involved in this equation has a discrete
spectrum. Its eigenfunctions and eigenvalues are found. The spectrum is a
shifted sequence of harmonic numbers. With the spectrum found, we represent the
expansion of the asymptotic in the fine structure constant in terms of multiple
polylogarithms. Using this representation, the exponentiation of the doubly
logarithmic corrections of the Sudakov form factor is recovered. It is pointed
out that the form factor of the skewed Sudakov regime is growing with the
virtuality of a fermion decreasing at a fixed virtuality of another fermion.Comment: 6 page
Comparison of experimental data and theoretical calculations for electrical resistivity and Hall coefficient in quasi-one-dimensional organic conductor (TMTSF)2PF6
The temperature dependences of the Hall coefficient and electrical
resistivity recently measured by Moser et al. [Phys. Rev. Lett. 84, 2674
(2000)] in the quasi-one-dimensional organic conductor (TMTSF)2PF6 are
quantitatively compared with our previous theoretical calculations [Synth. Met.
103, 2202 (1999); Eur. Phys. J. B 11, 385 (1999)]. We find a good agreement,
albeit not with a fully consistent set of parameters for the two quantities,
without appealing to the Luttinger liquid concept.Comment: 2 pages with 2 figures for ICSM-2000 proceedings. Uses elsart.cls and
synmet.cls, which are provided. V.2: one reference update
Anomalous temperature dependence of resistivity in quasi-one-dimensional conductors in a strong magnetic field
We present a heuristic, semiphenomenological model of the anomalous
temperature (T) dependence of resistivity Rxx recently observed experimentally
in the quasi-one-dimensional (Q1D) organic conductors of the (TMTSF)2X family
in moderately strong magnetic fields. We suggest that a Q1D conductor behaves
like an insulator (dRxx/dT<0), when its effective dimensionality is one, and
like a metal (dRxx/dT>0), when its effective dimensionality is greater than
one. Applying a magnetic field reduces the effective dimensionality of the
system and switches the temperature dependence of resistivity between the
insulating and metallic laws depending on the magnitude and orientation of the
magnetic field. We critically analyze whether various microscopic models
suggested in literature can produce such a behavior and find that none of the
models is fully satisfactory. In particular, we perform detailed analytical and
numerical calculations within the scenario of magnetic-field-induced
spin-density-wave precursor effect suggested by Gor'kov and find that the
theoretical results do not agree with the experimental observations.Comment: RevTeX, 17 pages, 7 figures. v.2: minor corrections; references are
added and updated v.3: minor corrections as in the published versio
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Observable Properties Of Double-Barred Galaxies In N-Body Simulations
Although at least one quarter of early-type barred galaxies host secondary stellar bars embedded in their large-scale primary counterparts, the dynamics of such double-barred galaxies are still not well understood. Recently we reported success at simulating such systems in a repeatable way in collisionless systems. In order to further our understanding of double-barred galaxies, here we characterize the density and kinematics of the N-body simulations of these galaxies. This will facilitate comparison with observations and lead to a better understanding of the observed double-barred galaxies. We find the shape and size of our simulated secondary bars are quite reasonable compared to the observed ones. We demonstrate that an authentic decoupled secondary bar may produce only a weak twist of the kinematic minor axis in the stellar velocity field, due to the relatively large random motion of stars in the central region. We also find that the edge-on nuclear bars are probably not related to boxy peanut-shaped bulges which are most likely to be edge-on primary large-scale bars. Another kinematic feature often present in our double-barred models is a ring-like feature in the fourth-order Gauss-Hermite moment h(4) maps. Finally, we demonstrate that the non-rigid rotation of the secondary bar causes its pattern speed to not be derived with great accuracy using the Tremaine-Weinberg method. We also compare with observations of NGC 2950, a prototypical double-barred early-type galaxy, which suggest that the nuclear bar may be rotating in the opposite sense as the primary.H.J.S. fellowshipUniversity of WashingtonNSF ITR PHY-0205413McDonald Observator
The Challenge of Light-Front Quantisation: Recent Results
We explain what is the challenge of light-front quantisation, and how we can
now answer it because of recent progress in solving the problem of zero modes
in the case of non-Abelian gauge theories. We also give a description of the
light-front Hamiltonian for SU(2) finite volume gluodynamics resulting from
this recent solution to the problem of light-front zero modes.Comment: 17 pages, lecture delivered by GBP at the XXXIV PNPI Winter School,
Repino, St.Petersburg, Russia, February 14-20, 2000, version to appear in the
Proceeding
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