Galactic longitude dependent Galactic model parameters

We present the Galactic model parameters for thin disc estimated by Sloan Digital Sky Survey (SDSS) data of 14 940 stars with apparent magnitudes $16<g_{o}\leq21$ in six intermediate latitude fields in the first Galactic quadrant. Star/galaxy separation was performed by using the $SDSS$ photometric pipeline and the isodensity contours in the $(g-r)_{0}-(r-i)_{0}$ two colour diagram. The separation of thin disc stars is carried out by the bimodal distribution of stars in the $(g-r)_{o}$ histogram, and the absolute magnitudes were evaluated by a procedure presented in the literature Bilir et al. (2005). Exponential density law fits better to the derived density functions for the absolute magnitude intervals $8<M(g)\leq9$ and $11<M(g)\leq12$, whereas sech/sech$^{2}$ laws are more appropriate for absolute magnitude intervals $9<M(g)\leq10$ and $10<M(g)\leq11$. We showed that the scaleheight and scalelength are Galactic longitude dependent. The average values and ranges of the scaleheight and the scalelength are $=220$ pc ($196\leq H \leq 234$ pc) and $=1900$ pc ($1561\leq h \leq 2280$ pc) respectively. This result would be useful to explain different numerical values claimed for those parameters obtained by different authors for the fields in different directions of the Galaxy.Comment: 28 pages, including 12 figures and 7 tables, accepted for publication in New Astronom

Statefinder parameters for quintom dark energy model

We perform in this paper a statefinder diagnostic to a dark energy model with two scalar fields, called "quintom", where one of the scalar fields has a canonical kinetic energy term and the other has a negative one. Several kinds of potentials are discussed. Our results show that the statefinder diagnostic can differentiate quintom model with other dark energy models.Comment: 11 pages, including 8 figures, added reference

Trying to understand the Standard Model parameters

We stress the importance of the circa 20 parameters in the Standard Model, which are not fixed by the model but only determined experimentally, as a window to the physics beyond the Standard Model. However, it is a tiny window in as far as these numbers contain only the information corresponding to about one line of text. Looking for a method to study these coupling and mass parameters, we put forward the idea of the Multiple Point Principle as a first step. This principle states that Nature adjusts the coupling and mass parameters so as to make many different vacuum states exist and have approximately the same energy densities (cosmological constants). As an illustrative application, we put up the proposal that a small increase (maybe only an infinitesimal one) in the value of the top quark coupling constant could lead to a new vacuum phase; in this new phase the binding of a bound state of 6 top quarks and 6 anti-top quarks becomes so strong as to become a tachyon and condense in the vacuum. Assuming the existence of a third degenerate vacuum at the fundamental energy scale, we present a solution to the hierarchy problem of why the ratio of the fundamental scale to the electroweak scale is so large. We also present a 5 parameter fit to the orders of magnitude of the quark-lepton masses and mixing angles in the Family Replicated Gauge Group Model. In this model, the Standard Model gauge group and a gauged B-L (baryon number minus lepton number) is extended to one set of gauge fields for each family of fermions.Comment: Institute address corrected and one reference adde

Statefinder Parameters for Tachyon Dark Energy Model

In this paper we study the statefinder parameters for the tachyon dark energy model. There are two kinds of stable attractor solutions in this model. The statefinder diagrams characterize the properties of the tachyon dark energy model. Our results show that the evolving trajectories of the attractor solutions lie in the total region and pass through the LCDM fixed point, which is different from other dark energy model.Comment: 5 pages, 5 figures, accepted by MPL