13,844 research outputs found
Threshold Effects And Perturbative Unification
We discuss the effect of the renormalization procedure in the computation of
the unification point for running coupling constants. We explore the effects of
threshold--crossing on the --functions. We compute the running of the
coupling constants of the Standard Model, between and , using a mass
dependent subtraction procedure, and then compare the results with ,
and with the -- function approximation. We also do this for the Minimal
Supersymmetric extension of the Standard Model. In the latter, the bounds on
susy masses that one obtains by requiring perturbative unification are
dependent, to some extent, on the procedure.Comment: 22 pages, REVTEX-2.1, 6 Post-Script figures are include
Spark Model for Pulsar Radiation Modulation Patterns
A non-stationary polar gap model first proposed by Ruderman & Sutherland
(1975) is modified and applied to spark-associated pulsar emission at radio
wave-lengths. It is argued that under physical and geometrical conditions
prevailing above pulsar polar cap, highly non-stationary spark discharges do
not occur at random positions. Instead, sparks should tend to operate in well
determined preferred regions. At any instant the polar cap is populated as
densely as possible with a number of two-dimensional sparks with a
characteristic dimension as well as a typical distance between adjacent sparks
being about the polar gap height. Our model differs, however, markedly from its
original 'hollow cone' version. The key feature is the quasi-central spark
driven by pair production process and anchored to the local pole of a
sunspot-like surface magnetic field. This fixed spark prevents the motion of
other sparks towards the pole, restricting it to slow circumferential drift
across the planes of field lines converging at the local pole. We argue that
the polar spark constitutes the core pulsar emission, and that the annular
rings of drifting sparks contribute to conal components of the pulsar beam. We
found that the number of nested cones in the beam of typical pulsar should not
excced three; a number also found by Mitra & Deshpande (1999) using a
completely different analysis.Comment: 31 pages, 8 figures, accepted by Ap
Dynamical light vector mesons in low-energy scattering of Goldstone bosons
We present a study of Goldstone boson scattering based on the flavor SU(3)
chiral Lagrangian formulated with vector mesons in the tensor field
representation. A coupled-channel channel computation is confronted with the
empirical s- and p-wave phase shifts, where good agreement with the data set is
obtained up to about 1.2 GeV. There are two relevant free parameters only, the
chiral limit value of the pion decay constant and the coupling constant
characterizing the decay of the rho meson into a pair of pions. We apply a
recently suggested approach that implements constraints from micro- causality
and coupled-channel unitarity. Generalized potentials are obtained from the
chiral Lagrangian and are expanded in terms of suitably constructed conformal
variables. The partial-wave scattering amplitudes are defined as solutions of
non-linear integral equations that are solved by means of an N/D ansatz.Comment: 15 pages, 8 figures, typos corrected, accepted for publication in
Physics Letters
The spark-associated soliton model for pulsar radio emission
We propose a new, self-consistent theory of coherent pulsar radio emission
based on the non-stationary sparking model of Ruderman & Sutherland (1975),
modified by Gil & Sendyk (2000) in the accompanying Paper I. According to these
authors, the polar cap is populated as densely as possible by a number of
sparks with a characteristic perpendicular dimension D approximately equal to
the polar gap height scale h, separated from each other also by about h. Each
spark reappears in approximately the same place on the polar cap for a time
scale much longer than its life-time and delivers to the open magnetosphere a
sequence of electron-positron clouds which flow orderly along a flux tube of
dipolar magnetic field lines. The overlapping of particles with different
momenta from consecutive clouds leads to effective two-stream instability,
which triggers electrostatic Langmuir waves at the altitudes of about 50
stellar radii. The electrostatic oscillations are modulationally unstable and
their nonlinear evolution results in formation of ``bunch-like'' charged
solitons. A characteristic soliton length along magnetic field lines is about
30 cm, so they are capable of emitting coherent curvature radiation at radio
wavelengths. The net soliton charge is about 10^21 fundamental charges,
contained within a volume of about 10^14 cm^3. For a typical pulsar, there are
about 10^5 solitons associated with each of about 25 sparks operating on the
polar cap at any instant. One soliton moving relativisticaly along dipolar
field lines with a Lorentz factor of the order of 100 generates a power of
about 10^21 erg/s by means of curvature radiation. Then the total power of a
typical radio pulsar can be estimated as being about 10^(27-28) erg/s.Comment: 27 pages, 5 figures, accepted by Ap
An Effective Field Theory Look at Deep Inelastic Scattering
This talk discusses the effective field theory view of deep inelastic
scattering. In such an approach, the standard factorization formula of a hard
coefficient multiplied by a parton distribution function arises from matching
of QCD onto an effective field theory. The DGLAP equations can then be viewed
as the standard renormalization group equations that determines the cut-off
dependence of the non-local operator whose forward matrix element is the parton
distribution function. As an example, the non-singlet quark splitting functions
is derived directly from the renormalization properties of the non-local
operator itself. This approach, although discussed in the literature, does not
appear to be well known to the larger high energy community. In this talk we
give a pedagogical introduction to this subject.Comment: 11 pages, 1 figure, To appear in Modern Physics Letters
Frequency dependence of pulsar radiation patterns
We report on new results from simultaneous, dual frequency, single pulse
observation of PSR B0329+54 using the Giant Metrewave Radio Telescope. We find
that the longitude separation of subpulses at two different frequencies (238
and 612 MHz) is less than that for the corresponding components in the average
profile. A similar behaviour has been noticed before in a number of pulsars. We
argue that subpulses are emitted within narrow flux tubes of the dipolar field
lines and that the mean pulsar beam has a conal structure. In such a model the
longitudes of profile components are determined by the intersection of the line
of sight trajectory with subpulse-associated emission beams. Thus, we show that
the difference in the frequency dependence of subpulse and profile component
longitudes is a natural property of the conal model of pulsar emission beam. We
support our conclusions by numerical modelling of pulsar emission, using the
known parameters for this pulsar, which produce results that agree very well
with our dual frequency observations.Comment: 24 pages, 8 figures. Accepted for publication in Ap
Parallel fabrication and single-electron charging of devices based on ordered, two-dimensional phases of organically functionalized metal nanocrystals
A parallel technique for fabricating single-electron, solid-state capacitance devices from ordered, two-dimensional closest-packed phases of organically functionalized metal nanocrystals is presented. The nanocrystal phases were prepared as Langmuir monolayers and subsequently transferred onto Al-electrode patterned glass substrates for device construction. Alternating current impedance measurements were carried out to probe the single-electron charging characteristics of the devices under both ambient and 77 K conditions. Evidence of a Coulomb blockade and step structure reminiscent of a Coulomb staircase is presented
- …