93 research outputs found
High- superconductivity by phase cloning
We consider a BCS-type model in the spin formalism and argue that the
structure of the interaction provides a mechanism for control over directions
of the spin \vect S other than , which is being controlled via the
conventional chemical potential. We also find the conditions for the appearance
of a high- superconducting phase.Comment: 11 pages, 5 figures v3: section 2 edite
Second-quantization picture of the edge currents in the fractional quantum Hall effect
We study the quantum theory of two-dimensional electrons in a magnetic field
and an electric field generated by a homogeneous background. The dynamics
separates into a microscopic and macroscopic mode. The latter is a circular
Hall current which is described by a chiral quantum field theory. It is shown
how in this second quantized picture a Laughlin-type wave function emerges.Comment: 12 pages, 1 figure, LaTeX; comments on the particle density and the
charge added, the figure improve
Time-ordering Dependence of Measurements in Teleportation
We trace back the phenomenon of "delayed-choice entanglement swapping" as it
was realized in a recent experiment to the commutativity of the projection
operators that are involved in the corresponding measurement process. We also
propose an experimental set-up which depends on the order of successive
measurements corresponding to noncommutative projection operators. In this case
entanglement swapping is used to teleport a quantum state from Alice to Bob,
where Bob has now the possibility to examine the noncommutativity within the
quantum history.Comment: 20 pages, 7 figures; v2; formalism of isometries elaborately
discussed, some changes in formulas, figure and reference added; typos
correcte
Emergence of order in selection-mutation dynamics
We characterize the time evolution of a d-dimensional probability
distribution by the value of its final entropy. If it is near the
maximally-possible value we call the evolution mixing, if it is near zero we
say it is purifying. The evolution is determined by the simplest non-linear
equation and contains a d times d matrix as input. Since we are not interested
in a particular evolution but in the general features of evolutions of this
type, we take the matrix elements as uniformly-distributed random numbers
between zero and some specified upper bound. Computer simulations show how the
final entropies are distributed over this field of random numbers. The result
is that the distribution crowds at the maximum entropy, if the upper bound is
unity. If we restrict the dynamical matrices to certain regions in matrix
space, for instance to diagonal or triangular matrices, then the entropy
distribution is maximal near zero, and the dynamics typically becomes
purifying.Comment: 8 pages, 8 figure
Asymptotic Neutrality of Large-Z Ions
Let N(Z) denote the number of electrons that a nucleus of charge Z binds in nonrelativistic quantum theory. It is proved that (N(Z))/Z → 1 as Z → ∞. The Pauli principle plays a critical role
Asymptotic Neutrality of Large-Z Ions
Let N(Z) denote the number of electrons that a nucleus of charge Z binds in nonrelativistic quantum theory. It is proved that (N(Z))/Z → 1 as Z → ∞. The Pauli principle plays a critical role
Electrostatic boundary value problems in the Schwarzschild background
The electrostatic potential of any test charge distribution in Schwarzschild
space with boundary values is derived. We calculate the Green's function,
generalize the second Green's identity for p-forms and find the general
solution. Boundary value problems are solved. With a multipole expansion the
asymptotic property for the field of any charge distribution is derived. It is
shown that one produces a Reissner--Nordstrom black hole if one lowers a test
charge distribution slowly toward the horizon. The symmetry of the distribution
is not important. All the multipole moments fade away except the monopole. A
calculation of the gravitationally induced electrostatic self-force on a
pointlike test charge distribution held stationary outside the black hole is
presented.Comment: 18 pages, no figures, uses iopart.st
Approach to equilibrium for a class of random quantum models of infinite range
We consider random generalizations of a quantum model of infinite range
introduced by Emch and Radin. The generalization allows a neat extension from
the class of absolutely summable lattice potentials to the optimal class
of square summable potentials first considered by Khanin and Sinai and
generalised by van Enter and van Hemmen. The approach to equilibrium in the
case of a Gaussian distribution is proved to be faster than for a Bernoulli
distribution for both short-range and long-range lattice potentials. While
exponential decay to equilibrium is excluded in the nonrandom case, it is
proved to occur for both short and long range potentials for Gaussian
distributions, and for potentials of class in the Bernoulli case. Open
problems are discussed.Comment: 10 pages, no figures. This last version, to appear in J. Stat. Phys.,
corrects some minor errors and includes additional references and comments on
the relation to experiment
Growth of perturbations in an expanding universe with Bose-Einstein condensate dark matter
We study the growth of perturbations in an expanding Newtonian universe with
Bose-Einstein condensate dark matter. We first ignore special relativistic
effects and derive a differential equation governing the evolution of the
density contrast in the linear regime taking into account quantum pressure and
self-interaction. This equation can be solved analytically in several cases. We
argue that an attractive self-interaction can enhance the Jeans instability and
fasten the formation of structures. Then, we take into account pressure effects
(coming from special relativity) in the evolution of the cosmic fluid and add
the contribution of radiation, baryons and dark energy (cosmological constant).
For a BEC dark matter with repulsive self-interaction (positive pressure) the
scale factor increases more rapidly than in the standard \Lambda CDM model
where dark matter is pressureless while for a BEC dark matter with attractive
self-interaction (negative pressure) it increases less rapidly. We study the
linear development of the perturbations in these two cases and show that the
perturbations grow faster in a BEC dark matter than in a pressureless dark
matter. This confirms a recent result of Harko (2011). Finally, we consider a
"dark fluid" with a generalized equation of state p=(\alpha \rho + k \rho
^2)c^2 having a component p=k \rho ^2 c^2 similar to a BEC dark matter and a
component p=\alpha \rho c^2 mimicking the effect of the cosmological constant
(dark energy). We find optimal parameters that give a good agreement with the
standard \Lambda CDM model assuming a finite cosmological constant
The LQG -- String: Loop Quantum Gravity Quantization of String Theory I. Flat Target Space
We combine I. background independent Loop Quantum Gravity (LQG) quantization
techniques, II. the mathematically rigorous framework of Algebraic Quantum
Field Theory (AQFT) and III. the theory of integrable systems resulting in the
invariant Pohlmeyer Charges in order to set up the general representation
theory (superselection theory) for the closed bosonic quantum string on flat
target space. While we do not solve the, expectedly, rich representation theory
completely, we present a, to the best of our knowledge new, non -- trivial
solution to the representation problem. This solution exists 1. for any target
space dimension, 2. for Minkowski signature of the target space, 3. without
tachyons, 4. manifestly ghost -- free (no negative norm states), 5. without
fixing a worldsheet or target space gauge, 6. without (Virasoro) anomalies
(zero central charge), 7. while preserving manifest target space Poincar\'e
invariance and 8. without picking up UV divergences. The existence of this
stable solution is exciting because it raises the hope that among all the
solutions to the representation problem (including fermionic degrees of
freedom) we find stable, phenomenologically acceptable ones in lower
dimensional target spaces, possibly without supersymmetry, that are much
simpler than the solutions that arise via compactification of the standard Fock
representation of the string. Moreover, these new representations could solve
some of the major puzzles of string theory such as the cosmological constant
problem. The solution presented in this paper exploits the flatness of the
target space in several important ways. In a companion paper we treat the more
complicated case of curved target spaces.Comment: 46 p., LaTex2e, no figure
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