Narrow Results

In this paper, we analyze the vacuum bosonic current associated with a massive charged scalar field propagating in a $(D+1)$-dimensional anti-de Sitter (AdS) bulk in the presence of an idealized carrying-magnetic-flux cosmic string and also a brane. We assume that the string is perpendicular to the brane, which is parallel to the AdS boundary. The brane divides the space in two regions with different properties of vacuum states. We investigate the only nonvanishing azimuthal components of the induced currents in both regions. To develop this analysis, we calculate first, for both regions, the positive frequency Wightman functions. These present contributions associated with the presence of a cosmic string only plus the other induced by the brane. In this paper, we consider only the contributions induced by the brane.

We present a whole frame for the cosmic strings, inflation and dark energy with the complex scalar field which can be regarded as the order parameter of our universe. One can find that the comic strings emerge in the zeros of the complex scalar field in the early universe. And with the evolution of complex scalar field, inflation and dark energy can be understood in this frame.

In a previous paper, we addressed the method of Abelian decomposition to the case of SU(N) Yang–Mills theory. Here, we extend the decomposition method further to the general case. With the Cartan–Weyl basis we decompose semisimple group connection and discuss the SO(3,1) group in particular. In terms of the vierbein projection, we propose two two-forms as the U(1) gauge fields in the SO(3,1) gauge theory and show that these two-forms are just the different cosmic string tensors. Meanwhile, these two-forms indicate that the cosmic strings appear naturally in the Lorentz spacetime, i.e. the torsion in the Riemann–Cartan spacetime is not necessary for the cosmic strings.

The equation of circular loops of cosmic string with time-dependent tension is studied in the Minkowski spacetime and Robertson–Walker universe. We found that, in the case where the tension depends on some power of the cosmic time, cosmic string loops with time-varying tension should not collapse to form a black hole if the power is lower than a critical value.

Inspired by condensed matter physics we propose a new, asymmetric, family of cosmic strings. These strings present a conical curvature singularity plus a surrounding region of alternating positive and negative curvature as the azimuthal angle is changed. Their sources include both positive and negative mass density regions.

We evaluate quasinormal mode frequencies for RN black hole spacetimes with cosmic string perturbed by a massless Dirac field, using Pöschl–Teller potential method. We find that only in the case of RN black hole having small charge, the effect due to cosmic string will dominate when perturbed by a negatively charged Dirac field, but if we are perturbing with positively charged Dirac field decay will be less in the case of black hole having cosmic string compared to the RN black hole without string.

The effect of cosmic string on the quasinormal modes (QNMs) of massless Dirac field perturbations were studied in different black hole spacetimes. Quasi-normal mode frequencies of massless Dirac field in Schwarzschild, RN extremal, SdS and near extremal SdS black hole spacetimes with cosmic string are obtained using WKB approximation. Our study shows a clear deviation in QNMs due to presence of cosmic string from those in the absence of string. The influence of cosmic string coded in the form of an increase in the oscillation frequency and damping time of QNMs.

Previously we investigated the Nambu–Goto string and the wiggly cosmic string in (3+1)-dimensional Schwarzschild black hole. As an extension the solutions in (3+1)-dimensional spherically symmetric charged black holes are investigated. The solution for the wiggly string exhibits open strings lying along the circular orbit in the equatorial plane outside horizon, while the Nambu–Goto string has only a point-like solution.

We consider the quantum scattering problem of a relativistic particle in (2 + 1)-dimensional cosmic string spacetime under the influence of a nontrivial boundary condition imposed on the solution of the Klein–Gordon equation. The solution is then shifted as consequence of the nontrivial boundary condition and the role of the phase shift is to produce an Aharonov–Bohm-like effect. We examine the connection between this phase shift and the electromagnetic and gravitational analogous of the Aharonov–Bohm effect and compare the present results with previous ones obtained in the literature, also considering non-relativistic cases.

In this paper, we investigate the trembling motion effect in the cosmic spacetime. The cosmic string was considered to be charged and carrying a magnetic flow. Zitterbewegung (ZB) is calculated based on the Dirac equation in the curved spacetime. An analytic expression for the electric current is obtained and analyzed.

We discuss the mechanism of energy mining from black holes by cosmic strings and its efficiency.

We calculate the energy radiated by a uniformly moving charged scalar particle in the spacetime of a point-like global monopole, for small solid angle deficit. We show that this energy is proportional to the cube of the velocity of the particle and to the cube of the Lorenz factor, in the non-relativistic and ultra-relativistic cases, respectively. We also determine the energy shifts of a hydrogen atom placed in the background spacetime of a cosmic string and we discuss the possibility that these shifts could provide a means of probing for the presence of this topological defect in the Universe.

In this paper we consider a charged massless scalar quantum field operator in the spacetime of an idealized cosmic string which presents a magnetic field confined in a cylindrical tube of finite radius. Three distinct situations are taken into account in this analysis. In three cases the axis of the infinitely long tube of radius R coincides with the cosmic string. Because we study the combined gravitational and electromagnetic Aharanov-Bohm effect, we calculate the vacuum polarization effects outside the tube.

We consider the presence of cosmic string induced density fluctuations in the universe at temperatures below the electroweak phase transition temperature. Resulting temperature fluctuations can restore the electroweak symmetry locally, depending on the amplitude of fluctuations and the background temperature. The symmetry will be spontaneously broken again in a given fluctuation region as the temperature drops there (for fluctuations with length scales smaller than the horizon), resulting in the production of baryon asymmetry. The time scale of the transition will be governed by the wavelength of fluctuation and, hence, can be much smaller than the Hubble time. This leads to strong enhancement in the production of baryon asymmetry for a second order electroweak phase transition as compared to the case when transition happens due to the cooling of the universe via expansion. For a two-Higgs extension of the Standard Model (with appropriate CP violation), we show that one can get the required baryon to entropy ratio if fluctuations propagate without getting significantly damped. If fluctuations are damped rapidly, then a volume factor suppresses the baryon production. Still, the short scale of the fluctuation leads to enhancement of the baryon to entropy ratio by at least 3–4 orders of magnitude compared to the conventional case of second order transition where the cooling happens due to expansion of the universe.

We calculated some Wilson loop functionals in a static sphere-symmetrical diagonal metric field, the Robertson–Walker (RW) metric field and a gravitational metric field established by cosmic string, respectively, and calculated the leading term W₍₂₎ and the term W₍₄₎ of a Wilson loop in Kerr metric field. Using the direction change of vector when it is parallel transported in the metric field of cosmic string, the cone symmetry of the metric field is demonstrated.

In this work, we give a general class of solutions of the spinning cosmic string in Einstein's theory of gravity. After treating same problem in Einstein–Cartan (EC) theory of gravity, the exact solution satisfying both exterior and interior space–times representing a spin fluid moving along the symmetry axis is presented in the EC theory. The existence of closed timelike curves in this space–time are also examined.

The standard electroweak model is extended by means of a second Brout–Englert–Higgs–doublet. The symmetry breaking potential is chosen in such a way that (i) the Lagrangian possesses a custodial symmetry, (ii) a stationary, axially symmetric ansatz of the bosonic fields consistently reduces the Euler–Lagrange equations to a set of differential equations. The potential involves, in particular, a direct interaction between the two doublets. Magnetic, stationary, axially-symmetric solutions of the classical equations are constructed. Some of them can be assimilated to embedded Nielsen–Olesen strings. From these solutions there are bifurcations and new solutions appear which exhibit the characteristics of the recently constructed twisted semilocal strings. A special emphasis is set on "doubly-twisted" solutions for which the two doublets present different time-dependent phase factors. They are regular and have a finite energy which can be lower than the energy of the embedded twisted solution. Electric-type solutions, such that the fields oscillate asymptotically far from the symmetry-axis, are also reported.

We have studied the quasinormal modes and the late-time tail behaviors of scalar, electromagnetic and gravitational perturbations in the Schwarzschild black hole pierced by a cosmic string. Although the metric is locally identical to that of the Schwarzschild black hole so that the presence of the string will not imprint in the motion of test particles, we found that quasinormal modes and the late-time tails can reflect physical signatures of the cosmic string. Compared with the scalar and electromagnetic fields, the gravitational perturbation decays slower, which would be more interesting to disclose the string effect in this background.

In this paper we investigate vacuum polarization effects associated with charged massive quantum fermionic fields in a six-dimensional cosmic string space-times considering the presence of a magnetic flux running along its core. We have shown that for specific values of the parameters which codify the presence of the cosmic string, and the fractional part of the ratio of the magnetic flux by the quantum one, a closed expression for the respective Green function is obtained. Adopting this result, we explicitly calculate the renormalized vacuum expectation value of the energy-momentum tensor, , and analyse this result in some limiting cases.

It has been known that in a wide class of direct gauge mediation models, the gaugino masses vanish at leading order in SUSY breaking. Recently, this phenomenon is understood in connection with the global structure of vacua in O'Raifeartaigh-type models. We review recent developments on this topic.