arXiv subjects

Je-An Gu

Publications and source records attributed to Je-An Gu.

27 records · Page 2Linked to original sources

arXiv2005

Casimir Effect in a Supersymmetry-Breaking Brane-World as Dark Energy

A new model for the origin of dark energy is proposed based on the Casimir effect in a supersymmetry-breaking brane-world. Supersymmetry is assumed to be preserved in the bulk while broken on a 3-brane. Due to the boundary conditions imposed on the compactified extra dimensions, there is an effective Casimir energy induced on the brane. The net Casimir energy contributed from the graviton and the gravitino modes as a result of supersymmetry-breaking on the brane is identified as the observed dark energy, which in our construction is a cosmological constant. We show that the smallness of the cosmological constant, which results from the huge contrast in the extra-dimensional volumes between that associated with the 3-brane and that of the bulk, is attainable under very relaxed conditions.

astro-ph↗

arXiv2004

The Interplay of Ultrahigh-Energy Cosmic Rays and Extra Dimensions

Regarding ultrahigh-energy cosmic rays (UHECRs) as a probe and extra dimensions as a possible ingredient of the fantastic ultrahigh-energy world, we discuss possible interplay between them. On the one hand small extra dimensions and Kaluza-Klein bursts present a feasible way to the origin of UHECRs. On the other hand large extra dimensions may change various interactions between particles at ultrahigh energies and therefore impact on air showers created by UHECRs. Conversely, UHECR data may tell us secrets veiled in extra dimensions.

hep-ph↗

arXiv2004

Evolution of the Universe with Flat Extra Dimensions

Evolution of a universe with homogeneous extra dimensions is studied with the benefit of a well-chosen parameter space that provides a systematic, useful, and convenient way for analysis. In this model we find a natural evolution pattern that entails not only stable extra dimensions in the radiation-dominated era, thereby preserving essential predictions in the standard cosmology, but also the present accelerating expansion while satisfying the limit on the variation of Newtonian gravitational constant. In this natural evolution pattern the extra dimensions tend to be stabilized automatically without resorting to artificial mechanisms in both the radiation-dominated and the matter-dominated era, as a wonderful feature for building models with extra dimensions. In addition, the naturalness of this evolution pattern that guarantees the late-time accelerating expansion of a matter-dominated universe presents a solution to the coincidence problem: why the accelerating phase starts at the present epoch. The feasibility of this evolution pattern for describing our universe is discussed.

astro-ph↗

arXiv2002

Can the quintessence be a complex scalar field?

In light of the recent observations of type Ia supernovae suggesting an accelerating expansion of the Universe, we wish in this paper to point out the possibility of using a complex scalar field as the quintessence to account for the acceleration. In particular, we extend the idea of Huterer and Turner in deriving the reconstruction equations for the complex quintessence, showing the feasibility of making use of a complex scalar field (instead of a real scalar field) while maintaining the uniqueness feature of the reconstruction for two possible situations, respectively. We discuss very briefly how future observations may help to distinguish the different quintessence scenarios, including the scenario with a positive cosmological constant.

astro-ph↗

arXiv2002

Accelerating Universe from the Evolution of Extra Dimensions

In this paper we propose that the accelerating expansion of the present matter-dominated universe, as suggested by the recent distance measurements of type Ia supernovae, is generated along with the evolution of space in extra dimensions. The Einstein equations are first analyzed qualitatively and then solved numerically, so as to exhibit explicitly these patterns of the accelerating expansion in this scenario. A fine-tuning problem associated with such a scenario is also described and discussed.

astro-ph↗

arXiv2002

A Way to the Dark Side of the Universe through Extra Dimensions

As indicated by Einstein's general relativity, matter and geometry are two faces of a single nature. In our point of view, extra dimensions, as a member of the {\em geometry face}, will be treated as a part of the {\em matter face} when they are beyond our poor vision, thereby providing dark energy sources effectively. The geometrical structure and the evolution pattern of extra dimensions therefore may play an important role in cosmology. Various possible impacts of extra dimensions on cosmology are investigated. In one way, the evolution of homogeneous extra dimensions may contribute to dark energy, driving the accelerating expansion of the universe. In the other way, both the energy perturbations in the ordinary three-space, combined with homogeneous extra dimensions, and the inhomogeneities in the extra space may contribute to dark matter. In this paper we wish to sketch the basic idea and show how extra dimensions may lead to the dark side of our universe.

astro-ph↗

arXiv2001

Spontaneous Symmetry Breaking, Non-minimal Coupling, and Cosmological Constant Problem

Treating the gravitational field as a dynamical field, we study the spontaneous symmetry breaking induced by a scalar field under its self-interaction and non-minimal interaction with gravity in four dimensional space-time. In particular, we explore the feasibility of inducing spontaneous symmetry breaking after introducing the non-minimal coupling, and discuss briefly the cosmological constant problem corresponding to the phase transition associated with the spontaneous symmetry breaking.

hep-th↗

arXiv2001

Spontaneous Symmetry Breaking in the Space-time of an Arbitrary Dimension

We propose a new scenario to implement spontaneous symmetry breaking in the space-time of an arbitrary dimension (D>2) by introducing the non-minimal coupling between the scalar field and the gravity. In this scenario, the usage of the familiar lambda Phi ^4 term, which is non-renormalizable for D >= 5, can be avoided altogether.

hep-th↗

arXiv2001

Stringy Spacetime Uncertainty as an Alternative to Inflation

In this paper we point out that the spacetime uncertainty relation proposed for string theory has strong cosmological implications that can solve the flatness problem and the horizon problem without the need of inflation. We make minimal assumptions about the very early universe.

hep-th↗