5671648
Time-dependent solution for a star immersed in a background radiation
We study a time-dependent and spherically symmetric solution with a starlike source. We show that this solution can be interpreted as an exterior solution of a contracting star which has a decreasing temperature and is immersed in a homogenous and isotropic background radiation. Distribution of the temperature in the fields and close-to-Schwarzschild approximation of the solution are studied. By identifying the radiation with the cosmic background one, we find that the close-to-Schwarzschild approximate solution is valid in a wide range in our solar system. Possible experimental tests of the solution are discussed briefly.
118482632
The Numerical Solution of Scalar Field for Nariai Case in 5D Ricci-flat SdS Black String Space with Polynomial Approximation
As one exact candidate of the higher dimensional black hole, the 5D Ricci-flat Schwarzschild-de Sitter black string space presents something interesting. In this paper, we give a numerical solution to the real scalar field around the Nariai black hole by the polynomial approximation. Unlike the previous tangent approximation, this fitting function makes a perfect match in the leading intermediate region and gives a good description near both the event and the cosmological horizons. We can read from our results that the wave is close to a harmonic one with the tortoise coordinate. Furthermore, with the actual radial coordinate the waves pile up almost equally near the both horizons.
14287684
Correspondence Between DGP Brane Cosmology and $5D$ Ricci-flat Cosmology
We discuss the correspondence between the DGP brane cosmology and 5D Ricci-flat cosmology by letting their metrics equal each other. By this correspondence, a specific geometrical property of the arbitrary integral constant I in DGP metric is given and it is related to the curvature of 5D bulk. At the same time, the relation of arbitrary functions μ and ν in a class of Ricci-flat solutions is obtained from DGP brane metric.
53459258
Reconstruction of Five-Dimensional Bounce Cosmological Models from Deceleration Factor
In this paper, we consider a class of five-dimensional Ricci-flat vacuum solutions, which contain two arbitrary functions μ(t) and ν(t). It is shown that μ(t) can be rewritten as a new arbitrary function f(z) in terms of redshift z and the f(z) can be determined by choosing particular deceleration parameters q(z) which gives early deceleration and late time acceleration. In this way, the 5D cosmological model can be reconstructed and the evolution of the universe can be determined.
123723006
PARTICLE MASSES IN KALUZA–KLEIN–GORDON THEORY AND THE REALITY OF EXTRA DIMENSIONS
To see how the effective 4-D mass of a particle is affected by the geometry of an ND space, we take the Klein–Gordon equation in 5-D and evaluate it in 4-D using two exact solutions of 5-D Kaluza–Klein theory. The mass (squared) turns out to be complex if the theory is independent of the extra coordinate, but can be made real if the wave function depends on an extra dimension which is physical. These results have significant implications for 10-D superstring theory.
49526339
Brane Formation and Cosmological Constraint on the Number of Extra Dimensions
Special relativity is generalized to extra dimensions and quantized energy levels of particles are obtained. By calculating the probability of particles' motion in extra dimensions at high temperature of the early universe, it is proposed that the branes may have not existed since the very beginning of the universe, but formed later. Meanwhile, before the formation, particles of the universe may have filled in the whole bulk, not just on the branes. This scenario differs from that in the standard big bang cosmology in which all particles are assumed to be in the 4D spacetime. So, in brane models, whether our universe began from a 4D big bang singularity is questionable. A cosmological constraint on the number of extra dimensions is also given which favors N ≥ 7.
119264434
f (R) Theories of supergravities and pseudo-supergravities
A bstractWe present f (R) theories of ten-dimensional supergravities, up to and including the quadratic order in fermion fields in action. They are obtained by performing the conformal scaling on the usual supergravities to the f (R) frame in which the dilaton becomes an auxiliary field and can be integrated out. The f (R) frame coincides with that of M-theory, D2-branes or NS-NS 5-branes. We study various BPS p-brane solutions and their near-horizon AdS × sphere geometries in the context of the f (R) theories. We find that new solutions emerge with global structures that do not exist in the corresponding solutions of the original supergravity description. In lower dimensions, We construct the f (R) theory of $\mathcal{N} = 2$, D = 5 gauged supergravity with a vector multiplet, and that for the four-dimensional U(1)4 gauged theory with three vector fields set equal. We find that some previously-known BPS singular “superstars” become wormholes in the f (R) theories. We also construct a large class of f (R) (gauged) pseudo-supergravities. In addition we show that the breathing mode in the Kaluza-Klein reduction of Gauss-Bonnet gravity on S1 is an auxiliary field and can be integrated out.
14851960
UV finite brane decay
The decay of an unstable D-brane via closed string emission and open string pair production is considered in subcritical string theory with a spacelike linear dilaton. The decay rate is given by the imaginary part of the annulus, which has ambiguities corresponding to the choices of incoming closed and open string vacua. An exact expression for the full annulus diagram is computed with a natural choice of incoming vacua. It is found that the ultraviolet divergences present in critical string theory in both of these processes are absent for any nonzero spacelike dilaton. Implications for the vexing issue of the tachyon dust are discussed.
664798
Stretched strings in noncommutative field theory
Motivated by recent discussions of IR-UV mixing in noncommutative field theories, we perform a detailed analysis of the nonplanar amplitudes of the bosonic open string in the presence of an external B field at the one-loop level. We carefully isolate, at the string theory level, the contribution which is responsible for the IR-UV behavior in the field theory limit. We show that it is a pure open string effect by deriving it from the factorization of the one-loop amplitude into the disk amplitudes of intermediate open string insertions. We suggest that it is natural to understand IR-UV mixing as the creation of intermediate ''stretched strings.'' (c) 2000 The American Physical Society.
118442403
Supersymmetric solutions in four-dimensional off-shell curvature-squared supergravity
Off-shell formulations of supergravities allow one to add closed-form higher-derivative super-invariants that are separately supersymmetric to the usual lower-derivative actions. In this paper we study four-dimensional off-shell N=1 supergravity where additional super-invariants associated with the square of the Weyl tensor and the square of the Ricci scalar are included. We obtain a variety of solutions where the metric describes domain walls, Lifshitz geometries, and also solutions of a kind known as gyratons. We find that in some cases the solutions can be supersymmetric for appropriate choices of the parameters. In some solutions the auxiliary fields may be imaginary. One may reinterpret these as real solutions in an analytically-continued theory. Since the supersymmetry transformation rules now require the gravitino to be complex, the analytically-continued theory has a "fake supersymmetry" rather than a genuine supersymmetry. Nevertheless, the concept of pseudo-supersymmetric solutions is a useful one, since the Killing spinor equations provide first-order equations for the bosonic fields.
118710617
Evidence of s-channel Single Top Quark Production in Events with one Charged Lepton and Bottom Quark Jets at CDF
We report an evidence of \textit{s}-channel single top quark production in $p\bar{p}$ collision at $\sqrt{s}= 1.96 \mathrm{TeV}$ using data with integrated luminosity of $9.4 \mathrm{fb}^{-1}$ collected by the Collider Detector at Fermilab (CDF). We select events with one charged lepton, large missing transverse energy and two bottom quark jets. The observed significance of the result is 3.8 standard deviation from background only prediction. We measure the inclusive cross section to be $1.41^{+0.44}_{-0.42}\mathrm{(stat+syst)} \mathrm{pb}$ assuming $m_t = 172.5 \mathrm{GeV}/c^2$.