725 research outputs found
Cosmological constant and Euclidean space from nonperturbative quantum torsion
Heisenberg's nonperturbative quantization technique is applied to the
nonpertrubative quantization of gravity. An infinite set of equations for all
Green's functions is obtained. An approximation is considered where: (a) the
metric remains as a classical field; (b) the affine connection can be
decomposed into classical and quantum parts; (c) the classical part of the
affine connection are the Christoffel symbols; (d) the quantum part is the
torsion. Using a scalar and vector fields approximation it is shown that
nonperturbative quantum effects gives rise to a cosmological constant and an
Euclidean solution.Comment: title is changed. arXiv admin note: text overlap with arXiv:1201.106
Bulk viscosity of strange quark matter: Urca versus non-leptonic processes
A general formalism for calculating the bulk viscosity of strange quark
matter is developed. Contrary to the common belief that the non-leptonic
processes alone give the dominant contribution to the bulk viscosity, the
inclusion of the Urca processes is shown to play an important role at
intermediate densities when the characteristic r-mode oscillation frequencies
are not too high. The interplay of non-leptonic and Urca processes is analyzed
in detailComment: 9 pages, 4 figures, v2: revised figures, no change in result
The Kerr theorem and multiparticle Kerr-Schild solutions
We discuss and prove an extended version of the Kerr theorem which allows one
to construct exact solutions of the Einstein-Maxwell field equations from a
holomorphic generating function of twistor variables. The exact
multiparticle Kerr-Schild solutions are obtained from generating function of
the form where are partial generating functions for
the spinning particles . Solutions have an unusual multi-sheeted
structure. Twistorial structures of the i-th and j-th particles do not feel
each other, forming a type of its internal space. Gravitational and
electromagnetic interaction of the particles occurs via the light-like singular
twistor lines. As a result, each particle turns out to be `dressed' by singular
pp-strings connecting it to other particles. We argue that this solution may
have a relation to quantum theory and to quantum gravity.Comment: 13 pages, 4 figures, revtex. Expressions for electromagnetic field
are correcte
Pseudoscalar Goldstone bosons in the color-flavor locked phase at moderate densities
The properties of the pseudoscalar Goldstone bosons in the color-flavor
locked phase at moderate densities are studied within a model of the
Nambu--Jona-Lasinio type. The Goldstone bosons are constructed explicitly by
solving the Bethe-Salpeter equation for quark-quark scattering in random phase
approximation. Main focus of our investigations are (i) the weak decay constant
in the chiral limit, (ii) the masses of the flavored (pseudo-) Goldstone bosons
for non-zero but equal quark masses, (iii) their masses and effective chemical
potentials for non-equal quark masses, and (iv) the onset of kaon condensation.
We compare our results with the predictions of the low-energy effective field
theory. The deviations from results obtained in the weak-coupling limit are
discussed in detail.Comment: 18 pages, 12 figure
Color-flavor locked superconductor in a magnetic field
We study the effects of moderately strong magnetic fields on the properties
of color-flavor locked color superconducting quark matter in the framework of
the Nambu-Jona-Lasinio model. We find that the energy gaps, which describe the
color superconducting pairing as well as the magnetization, are oscillating
functions of the magnetic field. Also, we observe that the oscillations of the
magnetization can be so strong that homogeneous quark matter becomes metastable
for a range of parameters. We suggest that this points to the possibility of
magnetic domains or other types of magnetic inhomogeneities in the quark cores
of magnetars.Comment: 12 pages, 3 figures. Version accepted for publication in Phys. Rev.
Absence of the London limit for the first-order phase transition to a color superconductor
We study the effects of gauge-field fluctuations on the free energy of a
homogeneous color superconductor in the color-flavor-locked (CFL) phase.
Gluonic fluctuations induce a strong first-order phase transition, in contrast
to electronic superconductors where this transition is weakly first order. The
critical temperature for this transition is larger than the one corresponding
to the diquark pairing instability. The physical reason is that the gluonic
Meissner masses suppress long-wavelength fluctuations as compared to the normal
conducting phase where gluons are massless, which stabilizes the
superconducting phase. In weak coupling, we analytically compute the
temperatures associated with the limits of metastability of the normal and
superconducting phases, as well as the latent heat associated with the
first-order phase transition. We then extrapolate our results to intermediate
densities and numerically evaluate the temperature of the fluctuation-induced
first-order phase transition, as well as the discontinuity of the diquark
condensate at the critical point. We find that the London limit of magnetic
interactions is absent in color superconductivity.Comment: 14 pages, 5 figure
Nonlinear Realization of the Local Conform-Affine Symmetry Group for Gravity in the Composite Fiber Bundle Formalism
A gauge theory of gravity based on a nonlinear realization (NLR) of the local
Conform-Affine (CA) group of symmetry transformations is presented. The coframe
fields and gauge connections of the theory are obtained. The tetrads and
Lorentz group metric are used to induce a spacetime metric. The inhomogenously
transforming (under the Lorentz group) connection coefficients serve as
gravitational gauge potentials used to define covariant derivatives
accommodating minimal coupling of matter and gauge fields. On the other hand,
the tensor valued connection forms serve as auxillary dynamical fields
associated with the dilation, special conformal and deformational (shear)
degrees of freedom inherent in the bundle manifold. The bundle curvature of the
theory is determined. Boundary topological invariants are constructed. They
serve as a prototype (source free) gravitational Lagrangian. The Bianchi
identities, covariant field equations and gauge currents are obtained.Comment: 24 pages. to appear in IJGMM
Bulk viscosity of spin-one color superconductors with two quark falvors
We consider the contribution of the Urca-type processes to the bulk viscosity
of several spin-one color-superconducting phases of dense two-flavor quark
matter. In the so-called transverse phases which are suggested to be
energetically favorable at asymptotic densities, the presence of ungapped
quasiparticle modes prevents that spin-one color superconductivity has a large
effect on the bulk viscosity. When all modes are gapped, as for one particular
color-spin-locked phase, the effect on the viscosity can be quite large, which
may have important phenomenological implications.Comment: 10 pages, 6 figures, Discussion is extended and several references
added. Version accepted for publication in Phys. Rev.
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