557 research outputs found
Construction of an all-sky camera
The "All-Sky" camera herein described is an outgrowth of
camera* operated in Alaska by the staff of the Geophysical Institute.
The principle has been of use in cloud studies and was
first used by C. W. Gar tie in for auroral photography. In its p resent
form the camera is capable of recording stable or slowly
moving auroral forms and is useful for synoptic "mapping of auroras
and detail studies. By proper scaling methods the camera
gives fa irly well defined mapping of aurora occurring within a
circle of 500 km radius and along the lengths of arcs, i.e . geomagnetic
East and West, to distances of about 1200 km. These
radii are based on an estimated lower border height of 100 km with
curved earth consideration.
Since the main use of the camera will be in high latitudes where
severe weather conditions occur, special effort has been made to
design a rugged instrument capable of withstanding high winds and
low temperatures. Ease of operation under adverse weather conditions
has also been a consideration. Whenever possible, use
has been made of commercially available parts to reduce construction
costs. An attempt has been made to simplify the construction
of those parts not commercially available. The camera
is designed to be built in a shop having a d rill press, lathe, milling
machine, welding equipment, and carpentry tools.
The recording element is a 16 mm movie camera with a 50 mm
f/l. 5 lens and equipped for lapse-time photography. The camera
views the entire sky in a convex mirror. A number of cameras
have been considered, two of which, the Bolex H-16 Leader and
the Kodak K-100, appear best suited with respect to cost and adaptability.
The Bolex H-16 is equipped for lapse-time photography
and requires no modification. The Bolex has the disadvantage of
only sixteen feet of film run per spring winding, hence, requires
attention each ten hours if one picture per minute is to be taken.
The Kodak K-100 must be modified for lapse photography but has
forty feet of useful film run and will operate without attention for
twenty-four hours at one frame per minute. Both these cameras
may be solenoid driven which allows variation of exposure times
with minimum effort.
An overall view of the camera is shown in Fig. 1. Fig. 2 shows t
the optical arrangement. Calculations made on the basis of Fig. 2
and the graph of height, angle, and distance, Fig. 3, allows the
location with respect to the earth's surface of any point on the
photographic image.Ye
Quantum tunneling of superconducting string currents
We investigate the decay of current on a superconducting cosmic string
through quantum tunneling. We construct the instanton describing tunneling in a
simple bosonic string model, and estimate the decay rate. The tunneling rate
vanishes in the limit of a chiral current. This conclusion, which is supported
by a symmetry argument, is expected to apply in general. It has important
implications for the stability of chiral vortons.Comment: 16 pages, 2 figure
Drum vortons in high density QCD
Recently it was shown that high density QCD supports of number of topological
defects. In particular, there are U(1)_Y strings that arise due to K^0
condensation that occurs when the strange quark mass is relatively large. The
unique feature of these strings is that they possess a nonzero K^+ condensate
that is trapped on the core. In the following we will show that these strings
(with nontrivial core structure) can form closed loops with conserved charge
and currents trapped on the string worldsheet. The presence of conserved
charges allows these topological defects, called vortons, to carry angular
momentum, which makes them classically stable objects. We also give arguments
demonstrating that vortons carry angular momentum very efficiently (in terms of
energy per unit angular momentum) such that they might be the important degrees
of freedom in the cores of neutron stars.Comment: 11 pages, accepted for publication in Physical Review
Fermionic massive modes along cosmic strings
The influence on cosmic string dynamics of fermionic massive bound states
propagating in the vortex, and getting their mass only from coupling to the
string forming Higgs field, is studied. Such massive fermionic currents are
numerically found to exist for a wide range of model parameters and seen to
modify drastically the usual string dynamics coming from the zero mode currents
alone. In particular, by means of a quantization procedure, a new equation of
state describing cosmic strings with any kind of fermionic current, massive or
massless, is derived and found to involve, at least, one state parameter per
trapped fermion species. This equation of state exhibits transitions from
subsonic to supersonic regimes while the massive modes are filled.Comment: 27 pages, 15 figures, uses ReVTeX. Shortened version, accepted for
publication in Phys. Rev.
Equation of state of cosmic strings with fermionic current-carriers
The relevant characteristic features, including energy per unit length and
tension, of a cosmic string carrying massless fermionic currents in the
framework of the Witten model in the neutral limit are derived through
quantization of the spinor fields along the string. The construction of a Fock
space is performed by means of a separation between longitudinal modes and the
so-called transverse zero energy solutions of the Dirac equation in the vortex.
As a result, quantization leads to a set of naturally defined state parameters
which are the number densities of particles and anti-particles trapped in the
cosmic string. It is seen that the usual one-parameter formalism for describing
the macroscopic dynamics of current-carrying vortices is not sufficient in the
case of fermionic carriers.Comment: 30 pages, 15 figures, uses ReVTeX, equation of state corrected,
comments and references added. Accepted for publication in Phys. Rev.
Neutral top-pion and lepton flavor violating processes
In the context of topcolor-assisted techicolor(TC2) models, we study the
contributions of the neutral top-pion to the lepton flavor
violating(LFV) processes and .
We find that the present experimental bound on gives severe
constraints on the free parameters of models. Taking into account these
constraints, we consider the processes generated by
top-pion exchange at the tree-level and the one loop level, and obtain
, , in most of
the parameter space.Comment: latex files,16 pages, 6 figures. Submitted to Phys. Rev.
Vortex Rings in two Component Bose-Einstein Condensates
We study the structure of the vortex core in two-component Bose-Einstein
condensates. We demonstrate that the order parameter may not vanish and the
symmetry may not be restored in the core of the vortex. In this case such
vortices can form vortex rings known as vortons in particle physics literature.
In contrast with well-studied superfluid , where similar vortex rings can
be stable due to Magnus force only if they move, the vortex rings in
two-component BECs can be stable even if they are at rest. This beautiful
effect was first discussed by Witten in the cosmic string context, where it was
shown that the stabilization occurs due to condensation of the second component
of the field in the vortex core. This second condensate trapped in the core may
carry a current along the vortex ring counteracting the effect of string
tension that causes the loop to shrink. We speculate that such vortons may have
been already observed in the laboratory. We also speculate that the
experimental study of topological structures in BECs can provide a unique
opportunity to study cosmology and astrophysics by doing laboratory
experiments.Comment: 21 pages, 2 figure
Topological Defects and CMB anisotropies : Are the predictions reliable ?
We consider a network of topological defects which can partly decay into
neutrinos, photons, baryons, or Cold Dark Matter. We find that the degree-scale
amplitude of the cosmic microwave background (CMB) anisotropies as well as the
shape of the matter power spectrum can be considerably modified when such a
decay is taken into account. We conclude that present predictions concerning
structure formation by defects might be unreliable.Comment: 14 pages, accepted for publication in PR
Axion Radiation from Strings
This paper revisits the problem of the string decay contribution to the axion
cosmological energy density. We show that this contribution is proportional to
the average relative increase when axion strings decay of a certain quantity
which we define. We carry out numerical simulations of the
evolution and decay of circular and non-circular string loops, of bent strings
with ends held fixed, and of vortex-antivortex pairs in two dimensions. In the
case of string loops and of vortex-antivortex pairs, decreases by
approximately 20%. In the case of bent strings, remains constant
or increases slightly. Our results imply that the string decay contribution to
the axion energy density is of the same order of magnitude as the
well-understood contribution from vacuum realignment.Comment: 29 pages, 10 figure
Constraints on diffuse neutrino background from primordial black holes
We calculated the energy spectra and the fluxes of electron neutrino emitted
in the process of evaporation of primordial black holes (PBHs) in the early
universe. It was assumed that PBHs are formed by a blue power-law spectrum of
primordial density fluctuations. We obtained the bounds on the spectral index
of density fluctuations assuming validity of the standard picture of
gravitational collapse and using the available data of several experiments with
atmospheric and solar neutrinos. The comparison of our results with the
previous constraints (which had been obtained using diffuse photon background
data) shows that such bounds are quite sensitive to an assumed form of the
initial PBH mass function.Comment: 18 pages,(with 7 figures
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