Single scale factor for the universe from the creation of radiation and matter till the present

A scheme for incorporating the creation of radiation and matter into the cosmological evolution is introduced so that it becomes possible to merge the times before and after the creation of radiation and matter in a single scale factor in Robertson-Walker metric. This scheme is illustrated through a toy model that has the prospect of constituting a basis for a realistic model.Comment: Minor typos are corrected, an acknowledgment is added, to be published in The European Physical Journal

A symmetry for vanishing cosmological constant in an extra dimensional toy model

We introduce a symmetry principle that forbids a bulk cosmological constant in six and ten dimensions. Then the symmetry is extended so that it insures absence of 4-dimensional cosmological constant induced by the six dimensional curvature scalar, at least, for a class of metrics. A small cosmological constant may be induced by breaking of the symmetry by a small amount.Comment: Typos are corrected. Two paragraphs and two references are added. To appear in PL

Is it possible to obtain cosmic accelerated expansion through energy transfer between different energy densities?

The equation of state of an energy density may be significantly modified by coupling it to another energy density. In the light of this observation we check the possibility of producing cosmic accelerated expansion in this way. In particular we consider the case where matter is converted to radiation (or vice versa by particle physics processes). We find that cosmic accelerated expansion can be obtained in this way only if an intermediate state with negative equation of state forms during the conversion.Comment: To be published in Physics of the Dark Univers

Fermion families, and chirality through extra dimensions

We give a simple model to explain the origin of fermion families, and chirality through the use of a domain wall placed in a five dimensional space-time.Comment: 12 page

Finite number of Kaluza-Klein modes, all with zero masses

Kaluza-Klein modes of fermions in a 5-dimensional toy model are considered. The number of Kaluza-Klein modes that survive after integration over extra dimensions is finite in this space. Moreover the extra dimensional piece of the kinetic term induces no mass for the higher Kaluza-Klein modes on contrary to the standard lore.Comment: Presentation is improved and typos are corrected, two appendices and some references are added. No change in the essential content of the paper. 11 page

Reconsidering extra time-like dimensions

In this study we reconsider the phenomenological problems related to tachyonic modes in the context of extra time-like dimensions. First we reconsider a lower bound on the size of extra time-like dimensions. Next we discuss the issues of spontaneous decay of stable fermions through tachyonic decays and disappearance of fermions due to tachyonic contributions to their self-energies. We find that the tachyonic modes due to extra time-like dimensions are less problematic than the tachyonic modes in the usual 4-dimensional setting because the most troublesome Feynman diagrams are forbidden once the conservation of momentum in the extra time-like dimensions is imposed.Comment: The version to appear in EPJ

Higgs field as the gauge field corresponding to parity in the usual space-time

We find that the local character of field theory requires the parity degree of freedom of the fields to be considered as an additional dicrete fifth dimension which is an artifact emerging due to the local description of space-time. Higgs field arises as the gauge field corresponding to this discrete dimension. Hence the noncommutative geometric derivation of the standard model follows as a manifestation of the local description of the usual space-time.Comment: 14 pages, latex, no figure

Extra dimensional metric reversal symmetry and its prospect for cosmological constant and zero-point energy problems, automatic pauli-villars-like regularization, and an interesting kaluza-klein spectrum

The metric reversal symmetry was introduced in the context of cosmological constant problem. Besides proposing a solution to the cosmological constant problem the metric reversal symmetry has also provided a framework for solution of the zero-point energy problem, an automatic Pauli-Villars-like regularization, and an interesting Kaluza- Klein spectrum with interesting phenomenological implications. In this talk I give a brief overall summary and discussion of these topics with their potential implications