19,113 research outputs found
Regularization of the Light-Cone Gauge Gluon Propagator Singularities Using Sub-Gauge Conditions
Perturbative QCD calculations in the light-cone gauge have long suffered from
the ambiguity associated with the regularization of the poles in the gluon
propagator. In this work we study sub-gauge conditions within the light-cone
gauge corresponding to several known ways of regulating the gluon propagator.
Using the functional integral calculation of the gluon propagator, we rederive
the known sub-gauge conditions for the theta-function gauges and identify the
sub-gauge condition for the principal value (PV) regularization of the gluon
propagator's light-cone poles. The obtained sub-gauge condition for the PV case
is further verified by a sample calculation of the classical Yang-Mills field
of two collinear ultrarelativistic point color charges. Our method does not
allow one to construct a sub-gauge condition corresponding to the well-known
Mandelstam-Leibbrandt prescription for regulating the gluon propagator poles.Comment: 19 pages, 2 figure
Classical Gluon Production Amplitude for Nucleus-Nucleus Collisions: First Saturation Correction in the Projectile
We calculate the classical single-gluon production amplitude in
nucleus-nucleus collisions including the first saturation correction in one of
the nuclei (the projectile) while keeping multiple-rescattering (saturation)
corrections to all orders in the other nucleus (the target). In our
approximation only two nucleons interact in the projectile nucleus: the
single-gluon production amplitude we calculate is order-g^3 and is
leading-order in the atomic number of the projectile, while resumming all
order-one saturation corrections in the target nucleus. Our result is the first
step towards obtaining an analytic expression for the first projectile
saturation correction to the gluon production cross section in nucleus-nucleus
collisions.Comment: 37 pages, 24 figure
Photovoltaic Current Response of Mesoscopic Conductors to Quantized Cavity Modes
We extend the analysis of the effects of electromagnetic (EM) fields on
mesoscopic conductors to include the effects of field quantization, motivated
by recent experiments on circuit QED. We show that in general there is a
photovoltaic (PV) current induced by quantized cavity modes at zero bias across
the conductor. This current depends on the average photon occupation number and
vanishes identically when it is equal to the average number of thermal
electron-hole pairs. We analyze in detail the case of a chaotic quantum dot at
temperature T_e in contact with a thermal EM field at temperature T_f,
calculating the RMS size of the PV current as a function of the temperature
difference, finding an effect ~pA.Comment: 4 pages, 2 figure
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The View of Russian Students on Whether Psychology is a Science
The Psychology as Science Scale (Friedrich, 1996) was administered to 525 psychology students from nine Russian universities to assess their beliefs about the nature of the discipline. About half of students (49.6%) generally agreed that psychology may be called a scientific discipline. Specifically, 71. 5% of the students agreed that psychology is a natural science, similar to biology, chemistry, and physics, 39. 9% of students agreed that psychological research is important and training in psychological methodology is necessary, and 43.1% of students agreed that human behavior is highly predictable. Students who took three methodology courses shared significantly stronger beliefs in the need for psychological research and the importance of training in methodology compared to students who did not take any methodology courses. Furthermore, students with a specialist degree had significantly stronger beliefs that psychology is a science compared to students who have just finished school. In terms of the effect of students’ career aspirations, students who wanted to be academic psychologists and clinicians had significantly stronger beliefs that psychology is a science compared to students who did not have clarity about their future careers. Regardless of the study limitations, these findings have potential implications for Russian psychology instructors
A fast genetically encoded fluorescent sensor for faithful in vivo acetylcholine detection in mice, fish, worms and flies
Here we design and optimize a genetically encoded fluorescent indicator, iAChSnFR, for the ubiquitous neurotransmitter acetylcholine, based on a bacterial periplasmic binding protein. iAChSnFR shows large fluorescence changes, rapid rise and decay kinetics, and insensitivity to most cholinergic drugs. iAChSnFR revealed large transients in a variety of slice and in vivo preparations in mouse, fish, fly and worm. iAChSnFR will be useful for the study of acetylcholine in all organisms
Driver Accelerator Design for the 10 kW Upgrade of the Jefferson Lab IR FEL
An upgrade of the Jefferson Lab IR FEL is now under construction. It will
provide 10 kW output light power in a wavelength range of 2-10 microns. The FEL
will be driven by a modest-sized 80-210 MeV, 10 mA energy-recovering
superconducting RF (SRF) linac. Stringent phase space requirements at the
wiggler, low beam energy, and high beam current subject the design to numerous
constraints. These are imposed by the need for both transverse and longitudinal
phase space management, the potential impact of collective phenomena (space
charge, wakefields, beam break-up (BBU), and coherent synchrotron radiation
(CSR)), and interactions between the FEL and the accelerator RF system. This
report addresses these issues and presents an accelerator design solution
meeting the requirements imposed by physical phenomena and operational
necessities.Comment: submission THC03 for LINAC200
Relativistic field theories in a magnetic background as noncommutative field theories
We study the connection of the dynamics in relativistic field theories in a
strong magnetic field with the dynamics of noncommutative field theories
(NCFT). As an example, the Nambu-Jona-Lasinio models in spatial dimensions are considered. We show that this connection is rather sophisticated.
In fact, the corresponding NCFT are different from the conventional ones
considered in the literature. In particular, the UV/IR mixing is absent in
these theories. The reason of that is an inner structure (i.e., dynamical
form-factors) of neutral composites which plays an important role in providing
consistency of the NCFT. An especially interesting case is that for a magnetic
field configuration with the maximal number of independent nonzero tensor
components. In that case, we show that the NCFT are finite for even and
their dynamics is quasi-(1+1)-dimensional for odd . For even , the NCFT
describe a confinement dynamics of charged particles. The difference between
the dynamics in strong magnetic backgrounds in field theories and that in
string theories is briefly discussed.Comment: 19 pages, REVTeX4, clarifications added, references added, to appear
in Phys. Rev.
Gauge invariance of dimension two condensate in Yang-Mills theory
Gauge independence of dimension two condensate in Yang-Mills theory is
demonstrated by using a noncommutative theory technique.Comment: 7 page
Quantum Geometry and its Implications for Black Holes
General relativity successfully describes space-times at scales that we can
observe and probe today, but it cannot be complete as a consequence of
singularity theorems. For a long time there have been indications that quantum
gravity will provide a more complete, non-singular extension which, however,
was difficult to verify in the absence of a quantum theory of gravity. By now
there are several candidates which show essential hints as to what a quantum
theory of gravity may look like. In particular, loop quantum gravity is a
non-perturbative formulation which is background independent, two properties
which are essential close to a classical singularity with strong fields and a
degenerate metric. In cosmological and black hole settings one can indeed see
explicitly how classical singularities are removed by quantum geometry: there
is a well-defined evolution all the way down to, and across, the smallest
scales. As for black holes, their horizon dynamics can be studied showing
characteristic modifications to the classical behavior. Conceptual and physical
issues can also be addressed in this context, providing lessons for quantum
gravity in general. Here, we conclude with some comments on the uniqueness
issue often linked to quantum gravity in some form or another.Comment: 16 pages, Plenary talk at ``Einstein's Legacy in the New Millenium,''
Puri, India, December 200
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