177 research outputs found
The partition function versus boundary conditions and confinement in the Yang-Mills theory
We analyse dependence of the partition function on the boundary condition for
the longitudinal component of the electric field strength in gauge field
theories. In a physical gauge the Gauss law constraint may be resolved
explicitly expressing this component via an integral of the physical
transversal variables. In particular, we study quantum electrodynamics with an
external charge and SU(2) gluodynamics. We find that only a charge distribution
slowly decreasing at spatial infinity can produce a nontrivial dependence in
the Abelian theory. However, in gluodynamics for temperatures below some
critical value the partition function acquires a delta-function like dependence
on the boundary condition, which leads to colour confinement.Comment: 14 pages, RevTeX, submitted to Phys. Rev.
Investigation of the Chaotic Dynamics of an Electron Beam with a Virtual Cathode in an External Magnetic Field
The effect of the strength of the focusing magnetic field on chaotic dynamic
processes occurring inan electron beam with a virtual cathode, as well as on
the processes whereby the structures form in the beamand interact with each
other, is studied by means of two-dimensional numerical simulations based on
solving a self-consistent set of Vlasov-Maxwell equations. It is shown that, as
the focusing magnetic field is decreased,the dynamics of an electron beam with
a virtual cathode becomes more complicated due to the formation andinteraction
of spatio-temporal longitudinal and transverse structures in the interaction
region of a vircator. The optimum efficiency of the interaction of an electron
beam with the electromagnetic field of the vircator isachieved at a
comparatively weak external magnetic field and is determined by the
fundamentally two-dimensional nature of the motion of the beam electrons near
the virtual cathode.Comment: 12 pages, 8 figure
Dijet Event Shapes as Diagnostic Tools
Event shapes have long been used to extract information about hadronic final
states and the properties of QCD, such as particle spin and the running
coupling. Recently, a family of event shapes, the angularities, has been
introduced that depends on a continuous parameter. This additional
parameter-dependence further extends the versatility of event shapes. It
provides a handle on nonperturbative power corrections, on non-global
logarithms, and on the flow of color in the final state.Comment: 18 pages, 3 figure
AdS_7/CFT_6, Gauss-Bonnet Gravity, and Viscosity Bound
We study the relation between the causality and the positivity of energy
bounds in Gauss-Bonnet gravity in AdS_7 background and find a precise
agreement. Requiring the group velocity of metastable states to be bounded by
the speed of light places a bound on the value of Gauss-Bonnet coupling. To
find the positivity of energy constraints we compute the parameters which
determine the angular distribution of the energy flux in terms of three
independent coefficients specifying the three-point function of the
stress-energy tensor. We then relate the latter to the Weyl anomaly of the
six-dimensional CFT and compute the anomaly holographically. The resulting
upper bound on the Gauss-Bonnet coupling coincides with that from causality and
results in a new bound on viscosity/entropy ratio.Comment: 21 page, harvmac; v2: reference adde
Stellar jitter from variable gravitational redshift: implications for RV confirmation of habitable exoplanets
A variation of gravitational redshift, arising from stellar radius
fluctuations, will introduce astrophysical noise into radial velocity
measurements by shifting the centroid of the observed spectral lines. Shifting
the centroid does not necessarily introduce line asymmetries. This is
fundamentally different from other types of stellar jitter so far identified,
which do result from line asymmetries. Furthermore, only a very small change in
stellar radius, ~0.01%, is necessary to generate a gravitational redshift
variation large enough to mask or mimic an Earth-twin. We explore possible
mechanisms for stellar radius fluctuations in low-mass stars. Convective
inhibition due to varying magnetic field strengths and the Wilson depression of
starspots are both found to induce substantial gravitational redshift
variations. Finally, we investigate a possible method for monitoring/correcting
this newly identified potential source of jitter and comment on its impact for
future exoplanet searches.Comment: 6 pages, 1 figure, 1 tabl
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