Axion dynamics in wormhole background

Classical and Quantum Gravity, 2008

The present paper reports interesting new features that wormhole solutions in the scalar field gravity theory have. To demonstrate these, we obtain, by using a slightly modified form of the Matos-Núñez algorithm, an extended class of asymptotically flat wormhole solutions belonging to Einstein minimally coupled scalar field theory. Generally, solutions in these theories do not represent traversable wormholes due to the occurrence of curvature singularities. However, the Ellis I solution of the Einstein minimally coupled theory, when Wick rotated, yields Ellis class III solution, the latter representing a singularity-free traversable wormhole. We see that Ellis I and III are not essentially independent solutions. The Wick rotated seed solutions, extended by the algorithm, contain two new parameters a and δ. The effect of the parameter a on the geodesic motion of test particles reveals some remarkable features. By arguing for Sagnac effect in the extended Wick rotated solution, we find that the parameter a can indeed be interpreted as a rotation parameter of the wormhole. The analyses reported here have wider applicability in that they can very well be adopted in other theories, including in the string theory.

Physical Review D, 1994

Mariano Cadoni (a),(c) and Marco Cavaglià (b),(d)

Physics & Astronomy International Journal, 2018

Noether symmetry has been invoked to explore the forms of a couple of coupling parameters and the potential appearing in a general scalar-tensor theory of gravity in the background of Robertson-Walker spacetime. Exact solutions of Einstein's field equations in the familiar Brans-Dicke, Induced gravity and a General non-minimally coupled scalar-tensor theories of gravity have been found using the conserved current and the energy equation, after being expressed in a set of new variables. Noticeably, the form of the scale factors remains unaltered in all the three cases and represents cosmological Lorentzian wormholes, analogous to the Euclidean ones. While classical Euclidean wormholes requires an imaginary scalar field, the Lorentzian wormhole do not, and the solutions satisfy the weak energy condition.

Physical Review D, 1989

We adapt the rules, used by Coleman in the context of Euclidean gravity to show that the cosmological constant vanishes, to the simpler case of a scalar field theory. We compute oneand twopoint functions in a variety of examples and in various approximations. We discover cases where wormholes make first-order phase transitions disappear, but permit second-order transitions. We find a peculiar propagator for a scalar field coupled quadratically to wormholes in the Hartree-Fock approximation.

2013

Wormhole physics as embodied by a modified Wheeler De Witt equation as given by Crowell inter connects with how to write a quintessence version of the 'cosmological constant'. The resulting value for the 'cosmological constant' is for wormholes for reasons stated in this document, using a modified form of the Weiner-Nordstrom metric, with no charge Q.

The European Physical Journal C

The present study analyses the wormhole solution both in the dRGT-f(R, T) massive gravity and Einstein massive gravity. In both the models, the anisotropic pressure solution in ultrastatic wormhole geometry gives rise to the shape function that involves massive gravity parameters $$ \gamma $$ γ and $$ \Lambda $$ Λ . However, the terms consisting of $$ \gamma $$ γ and $$ \Lambda $$ Λ acts in such a way that the spacetime loses asymptotic flatness. Similar to the black hole solution in massive gravity, this inconsistency arises due to the repulsive effect of gravity which can be represented by the photon deflection angle that goes negative after a certain radial distance. It is investigated that the repulsive effect induced in the massive gravitons push the spacetime geometry so strongly that the asymptotic flatness is effected. On the other hand, in this model, one can have a wormhole with ordinary matter at the throat that satisfies all the energy conditions while the negative energ...

The European Physical Journal C

We present a flat emergent universe (EU) in Einstein gravity with non-linear equation of state (nEoS) in the usual four and in higher dimensions. The EU is assumed to evolve from an initial Einstein’s static universe (ESU) in the infinite past. For a homogeneous Ricci scalar we determine the shape function and obtain a new class of dynamical wormholes that permits EU. The nEoS $$p= A\rho -B \sqrt{\rho _o \rho }$$ p = A ρ - B ρ o ρ is equivalent to three different cosmic fluids which is identified with barotropic fluid for a given A. We obtain EU models in flat, closed and open universes and tested the null energy condition (NEC). At the throat of the wormhole which is recognized as the seed of ESU, we tested the NEC for a given size of the neck. As the EU evolves from an asymptotic past and approaches $$t=0$$ t = 0 , it is found that NEC does not respect. This triggers the onset of interactions at $$t=t_i$$ t = t i , and a realistic flat EU scenario can be obtained in four and in hi...

Physical Review D, 2016

Motivated by recent proposals of possible wormhole existence in galactic halos, we analyse the cosmological evolution of wormhole solutions in modified f (R) gravity. We construct a dynamical wormhole that asymptotically approaches FLRW universe, with supporting material going to the perfect isotropic fluid described by the equation of state for radiation and matter dominated universe respectively. Our analysis is based on an approximation of a small wormhole-a wormhole that can be treated as matched with the FLRW metric at some radial coordinate much smaller than the Hubble radius, so that cosmological boundary conditions are satisfied. With a special interest in viable wormhole solutions, we refer to the results of reconstruction procedure and use f (R) functions which lead to the experimentally confirmed ΛCDM expansion history of the universe. Solutions we find imply no need for exotic matter near the throat of considered wormholes, while in the limit of f (R) = R this need is always present during radiation and matter dominated epoch.

Nuclear Physics B, 1990

Recently, Hosoya and Ogura found a wormhole instanton solution with a nontrivial SU(2) magnetic field. In this paper, we identify their solution with the gravitating meron configuration of the SU(2) gauge theory . In addition, we also find a generalized Yang-Mills wormhole solution with nontrivial electric and magnetic fields . These correspond to the "nested" meron wormholes. Fermion dynamics on these wormhole backgrounds and implications for low-energy physics are also discussed. * Alternatively, one may derive eq. (6) directly from taking the covariant derivative of eq . (5) . These two alternatives give the same consistent equation of motion.

Arxiv preprint arXiv:1004.2863, 2010

We find the full symmetries of the Wheeler-DeWitt equation for the Hawking and Page wormhole model and an axion-dilaton string cosmology. We show that the Wheeler-DeWitt Hamiltonian admits an U (1, 1) hidden symmetry for the Hawking and Page model and U (2, 1) for the axiondilaton string cosmology. If we consider the existence of matter-energy renormalization, for each of these models we find that the Wheeler-DeWitt Hamiltonian accept an additional SL(2, R) dynamical symmetry. In this case, we show that the SL(2, R) dynamical symmetry generators transform the states from one energy Hilbert eigensubspace to another.