Nonzero Energy Density Research Articles

Tachyon Matter

It is shown that classical decay of unstable D-branes in bosonic and superstring theories produces pressureless gas with non-zero energy density. The energy density is stored in the open string fields, even though around the minimum of the tachyon potential there are no open string degrees of freedom. We also give a description of this phenomenon in an effective field theory.

Q-ball formation in the wake of Hubble-induced radiative corrections

We discuss some interesting aspects of the $\rm Q$-ball formation during the early oscillations of the flat directions. These oscillations are triggered by the running of soft $({\rm mass})^2$ stemming from the nonzero energy density of the Universe. However, this is quite different from the standard $\rm Q$-ball formation. The running in presence of gauge and Yukawa couplings becomes strong if $m_{1/2}/m_0$ is sufficiently large. Moreover, the $\rm Q$-balls which are formed during the early oscillations constantly evolve, due to the redshift of the Hubble-induced soft mass, until the low-energy supersymmtery breaking becomes dominant. For smaller $m_{1/2}/m_0$, $\rm Q$-balls are not formed during early oscillations because of the shrinking of the instability band due to the Hubble expansion. In this case the $\rm Q$-balls are formed only at the weak scale, but typically carry smaller charges, as a result of their amplitude redshift. Therefore, the Hubble-induced corrections to the flat directions give rise to a successful $\rm Q$-ball cosmology.

Hubble-induced radiative corrections and Affleck-Dine baryogenesis

We examine the viability of the Affleck-Dine mechanism for baryogenesis under radiatively induced running of soft breaking $({\rm mass})^2$ of the flat directions stemming from non-zero energy density of the inflaton during inflation. A major difference from analogous phenomenological studies is that the horizon radius provides a natural infrared cut-off to the quantum corrections in this case. We identify different scenarios which may arise and point out that the $H_{u}L$ flat direction remains the most promising flat direction, since it is largely independent of uncertainties about high scale physics and details of the inflationary model.

Casimir effect around a screw dislocation

In this work, it is shown that a non-zero vacuum energy density (the Casimir energy) for a scalar field appears in a continuous elastic solid due to the presence of a topological defect, the screw dislocation. An exact expression is obtained for this energy density in terms of the Burgers vector describing the defect, for zero and finite temperature.

Casimir effect around a screw dislocation

In this work, it is shown that a non-zero vacuum energy density (the Casimir energy) for a scalar field appears in a continuous elastic solid owing to the presence of a topological defect, the screw dislocation. An exact expression is obtained for this energy density in terms of the Burgers vector describing the defect, for zero temperature and finite temperatures.

A dying universe: the long-term fate and evolutionof astrophysical objects

This paper outlines astrophysical issues related to the long-term fate of the universe. The authors consider the evolution of planets, stars, stellar populations, galaxies, and the universe itself over time scales that greatly exceed the current age of the universe. Their discussion starts with new stellar evolution calculations which follow the future evolution of the low-mass (M-type) stars that dominate the stellar mass function. They derive scaling relations that describe how the range of stellar masses and lifetimes depends on forthcoming increases in metallicity. They then proceed to determine the ultimate mass distribution of stellar remnants, i.e., the neutron stars, white dwarfs, and brown dwarfs remaining at the end of stellar evolution; this aggregate of remnants defines the 'final stellar mass function.' At times exceeding \ensuremath{\sim}1--10 trillion years, the supply of interstellar gas will be exhausted, yet star formation will continue at a highly attenuated level via collisions between brown dwarfs. This process tails off as the galaxy gradually depletes its stars by ejecting the majority and driving a minority toward eventual accretion onto massive black holes. As the galaxy disperses, stellar remnants provide a mechanism for converting the halo dark matter into radiative energy. Posited weakly interacting massive particles are accreted by white dwarfs, where they subsequently annihilate with each other. Thermalization of the decay products keeps the old white dwarfs much warmer than they would otherwise be. After accounting for the destruction of the galaxy, the authors consider the fate of the expelled degenerate objects (planets, white dwarfs, and neutron stars) within the explicit assumption that proton decay is a viable process. The evolution and eventual sublimation of these objects is dictated by the decay of their constituent nucleons, and this evolutionary scenario is developed in some detail. After white dwarfs and neutron stars have disappeared, galactic black holes slowly lose their mass as they emit Hawking radiation. This review finishes with an evaluation of cosmological issues that arise in connection with the long-term evolution of the universe. Special attention is devoted to the relation between future density fluctuations and the prospects for continued large-scale expansion. The authors compute the evolution of the background radiation fields of the universe. After several trillion years, the current cosmic microwave background will have redshifted into insignificance; the dominant contribution to the radiation background will arise from other sources, including stars, dark-matter annihilation, proton decay, and black holes. Finally, the authors consider the dramatic possible effects of a nonzero vacuum energy density.

Casimir effect around disclinations

This communication concerns the structure of the electromagnetic quantum vacuum in a disclinated insulator. It is shown that a nonzero vacuum energy density appears when the rotational symmetry of a continuous insulating elastic medium is broken by a disclination. An explicit expression is given for this Casimir energy density in terms of the parameter describing the disclination.

Exact Disk Solution of the Einstein Equation

The 4-soliton solution with complex pole trajectories to the vacuum Einstein equation is studied. The solution describes a static and axisymmetric gravitational field with asymptotic flatness, which is produced by a thin disk. We obtain the energy-momentum tensor of the to reveal its properties. The soliton technique 1 ) to solve the gravitational field equation gave us a new viewpoint on the exact solutions of the vacuum Einstein equation. There is an infinite series of solutions which are characterized by the soliton number n. In the stationary case with axial symmetry the series includes the Kerr-NUT solution as a 2-soliton solution and the Tomimatsu-Sato solution as a certain limit of 4-soliton solution. In the static case 2 ),3) there is an infinite series of the Weyl solutions, which is interpreted as a nonlinear superposition of multi-Weyl solutions. Two of the present authors 3 ),4) showed that the soliton technique gives not only these series of solutions but a series of ring-type solutions by adopting complex pole trajectories in the static case. The first non-trivial example of this series is the Weyl solution expressed in the oblate spheroidal coordinates,5) which has a ring-type curvature singularity. In our classification this solution is interpreted as the 2-soliton solution with non-complex-conjugate pole trajectories. The next example is the 4-soliton solution in which there are two types. One is just a nonlinear superposition of the above 2-soliton solutions, which has two ring-type singularities with different radii. The other, which is more important, is the 4-soliton solution constructed from two pairs of complex conjugate pole trajectories. This was referred to as the two­ ring solution, because the curvature invariants have finite limits at two rings although the metric coefficients diverge there. This fact contrasts with the fact that the curvature invariants diverge at the ring in the 2-soliton case. The purpose of this paper is to study the detailed structure of the two-ring solution. It will be shown that the solution should be called a solution rather than a ring solution. The properties of the will be also clarified by calculating the energy-momentum tensor. In the next section we give the solution in an explicit form and investigate its mathematical structure. From this we find that the plane containing the rings is separated into a regular region inside the inner ring and a region with the discontinuity of curvature outside the inner ring. We shall call this outer region a disk because of its non-zero energy density as will be.discussed in § 3. The is further divided into two parts by the outer ring. In § 3 we obtain the

Constraints on vacuum decay from the microwave background

view Abstract Citations (37) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Constraints on Vacuum Decay from the Microwave Background Overduin, J. M. ; Wesson, P. S. ; Bowyer, S. Abstract We consider the possible decay of a vacuum with nonzero energy density into radiation. This is one way to introduce a time-varying cosmological constant, which has been suggested as a means of resolving the cosmological constant problem. We concentrate on the model of Freese et al., in which the vacuum energy density is given as a fraction x/(1 - x) of the energy density of radiation. Using equations for the visible extragalactic background light and assuming that the vacuum decay energy is converted entirely into photons with a Planckian spectrum, we show that the decay process would be capable of contributing significantly to the intensity of the cosmic microwave background. Comparison with COBE observations leads to the constraint x is equal to or less than 0.001, which is stronger than the upper limit of 0.07 obtained previously by Freese et al. from considerations of primordial nucleosynthesis. Publication: The Astrophysical Journal Pub Date: February 1993 DOI: 10.1086/172253 Bibcode: 1993ApJ...404....1O Keywords: Cosmology; Decay; Microwaves; Relic Radiation; Vacuum; Computational Astrophysics; Cosmic Background Explorer Satellite; Dark Matter; Radiant Flux Density; Astrophysics; COSMOLOGY: DARK MATTER; COSMOLOGY: THEORY; COSMOLOGY: COSMIC MICROWAVE BACKGROUND; RADIATION MECHANISMS: MISCELLANEOUS full text sources ADS |

The cosmological constant and cold dark matter

THE cold dark matter (CDM) model1–4 for the formation and distribution of galaxies in a universe with exactly the critical density is theoretically appealing and has proved to be durable, but recent work5–8 suggests that there is more cosmological structure on very large scales (l> 10 h–1 Mpc, where h is the Hubble constant H0 in units of 100 km s–1 Mpc–1) than simple versions of the CDM theory predict. We argue here that the successes of the CDM theory can be retained and the new observations accommodated in a spatially flat cosmology in which as much as 80% of the critical density is provided by a positive cosmological constant, which is dynamically equivalent to endowing the vacuum with a non-zero energy density. In such a universe, expansion was dominated by CDM until a recent epoch, but is now governed by the cosmological constant. As well as explaining large-scale structure, a cosmological constant can account for the lack of fluctuations in the microwave background and the large number of certain kinds of object found at high redshift.

General relativistic fluid spheres with nonzero vacuum energy density

Bounds are developed for the ratios M/R and m/R for fluid spheres in asymptotically de Sitter or anti-de Sitter space-times, where M is the mass of the fluid sphere, and m is the total mass interior to R: M plus the interior vacuum energy. This represents a generalization of the work of Buchdahl to the case of a nonvanishing vacuum energy density. In the asymptotically de Sitter case, it is possible to construct models which have m/r→ 1/2 . Further, it is shown that static fluid spheres can exist in an asymptotically de Sitter space with vacuum energy density ρv only if their radius satisfies R≤(8πρv)1/2, a maximum radius smaller by a factor of 3−1/2 than the horizon size of the de Sitter space in the absence of a fluid sphere. If the vacuum energy density is negative, then the ratio m/R is shown to be bounded above by the asymptotically flat limit of (4)/(9), and the radius of a positive total mass (m) sphere is shown to be bounded above by R<(2π‖ρv‖)−1/2.

Why is the universe so large?

S. W. Hawking's proposal for the wave function of the universe, if correct, determines the conditional probabilities for all properties of the universe. In a simple minisuperspace model it predicts that at any given nonzero energy density, the universe is most probably infinitely large.

On energy flux and group velocity

Inhomogeneous plane wave solutions to the wave equations for a linear isotropic elastic solid and a linear isotropic dielectric are shown to possess energy flux velocity vectors which are non-coincident with corresponding group velocity vectors. In contrast to free surface waves, these examples imply a driving constraint and have an associated non-zero Lagrangian energy density.

Phase properties of some photon states with nonzero energy density

We describe some photon states with nonzero energy density in the whole space; these states are obtained by taking a finite number of photons within a finite box and letting the volume and the number of photons go to infinity according to usual procedure in statistical mechanics. In such a limit we describe an observable phase operator; we investigate its properties both in the case of free field and in the case of coupling with prescribed classical sources. Finally we give a quantum description of uniform static field.

Finite-dimensional Gel’fand-Yaglom equations for arbitrary integral spin

A method is given for the construction of Gel’fand-Yaglom equations for integral spin particles with nonzero mass and energy density positive definite. The equations for a particle of spin 3 is explicitly derived.