1,720,981 research outputs found
Minimal coupling of the Kalb-Ramond field to a scalar field
No full textWe study the direct interaction of an antisymmetric Kalb-Ramond field with a scalar particle derived from a gauge principle. The method outlined in this paper to define a covariant derivative is applied to a simple model leading to a linear coupling between the fields. Although no conserved Noether charge exists, a conserved topological current comes out from the antisymmetry properties of the Kalb-Ramond field. Some interesting features of this current are pointed out. Possible applications of our results to cosmology and to the theory of three-dimensional Josephson junction arrays are envisaged
One-loop analysis with nonlocal boundary conditions
No full textIn the 1980s, Schröder studied a quantum mechanical model where the stationary states of Schrödinger’s
equation obey nonlocal boundary conditions on a circle in the plane. For such a problem, we perform a
detailed one-loop calculation for three choices of the kernel characterizing the nonlocal boundary
conditions. In such cases, the ζ(0) value is found to coincide with the one resulting from Robin boundary
conditions. The detailed technique here developed may be useful for studying one-loop properties of
quantum field theory and quantum gravity if nonlocal boundary conditions are imposed
Fermi, Majorana and the statistical model of atoms
No full textWe give an account of the appearance and first developments of the statistical model of atoms proposed by Thomas and Fermi, focusing on the main results achieved by Fermi and his group in Rome. Particular attention is addressed to the unknown contribution to this subject by Majorana, anticipating some important results reached later by leading physicists
Majorana and the quasi-stationary states in nuclear physics
No full textA complete theoretical model describing artificial disintegration of nuclei by bombardment with alpha-particles, developed by Majorana as early as 1930, is discussed in detail jointly with the basic experimental evidences that motivated it. By following the quantum dynamics of a state resulting from the superposition of a discrete state with a continuum one, whose interaction is described by a given potential term, Majorana obtained (among the other predictions) the explicit expression for the integrated cross section of the nuclear process, which is the directly measurable quantity of interest in the experiments. Although this is the first application of the concept of quasi-stationary states to a Nuclear Physics problem, it seems also that the unpublished Majorana work anticipates by several years the related seminal paper by Fano on Atomic Physics
Second discontinuity in the specific heat of two-phase superconductors
No full textThe recently proposed theoretical model of superconductors endowed with two distinct superconducting phases and critical temperatures is further analyzed by introducing two distinct order parameters, described by two scalar fields which condensate at different temperatures. We find some deviations in basic thermodynamical quantities with respect to the Ginzburg-Landau one-phase superconductors. In particular, in contrast to the usual case where only one jump in specific heat takes place at the normal-superconductor transition temperature, we actually predict an additional discontinuity for C-V when passing from a superconducting phase to the other one. (c) 2007 Elsevier B.V. All rights reserved
Magnetic properties of two-phase superconductors
No full textWe have recently proposed a theoretical model for superconductors endowed with two distinct superconducting phases, described by two scalar order parameters which condensate at different critical temperatures. On analyzing the magnetic behavior of such systems, we have found some observable differences with respect to the case of ordinary Ginzburg-Landau superconductors. In particular, at low temperature the London penetration length is strongly reduced and the Ginzburg-Landau parameter K becomes a function of temperature. By contrast, in the temperature region between the two-phase transitions K is constant and the system is a type-I or a type-II superconductor depending on the ratio between the critical temperatures. (c) 2008 Elsevier B.V. All rights reserved
A generalization of the Ginzburg-Landau theory to p-wave superconductors
No full textWe succeed in building up a straightforward theoretical model for spin-triplet p-wave superconductors, by introducing a second-order parameter and a nonlinear interaction between the two mean fields in the Ginzburg Landau theory. Such interaction breaks the isotropy of the original medium and allows pairs of electrons to arrange into S = 1 Cooper pairs. The present model predicts a thermodynamical and magnetic behavior analogous to that observed in conventional s-wave superconductors
Non-commutative Einstein equations and Seiberg-Witten map
No full textThe Seiberg–Witten map is a powerful tool in non-commutative field theory, and it
has been recently obtained in the literature for gravity itself, to first order in noncommutativity.
This paper, relying upon the pure-gravity form of the action functional
considered in Ref. 2, studies the expansion to first order of the non-commutative Einstein
equations, and whether the Seiberg–Witten map can lead to a solution of such
equations when the underlying classical geometry is Schwarzschild. We find that, if one
first obtains the non-commutative field equations by varying the action of Ref. 2 with
respect to all non-commutative fields, and then tries to solve these equations by expressing
the non-commutative fields in terms of the commutative ones via Seiberg–Witten
map, no solution of these equations can be obtained when the commutative background
is Schwarzschild
Quantum phase excitations in Ginzburg-Landau superconductors
No full textWe give a straightforward generalization of the Ginzburg-Landau theory for superconductors where the scalar phase field is replaced by an antisymmetric Kalb-Ramond field. We predict that at very low temperatures, where quantum phase effects are expected to play a significant role, the presence of vortices destroys superconductivity. A physical scenario behind the model proposed, which can be directly tested by experiments, is envisaged
SPACE-TIME SYMMETRY RESTORATION IN COSMOLOGICAL MODELS WITH KALB-RAMOND AND SCALAR FIELDS
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