Dilaton Cosmology, Noncommutativity and Generalized Uncertainty Principle

The effects of noncommutativity and of the existence of a minimal length on the phase space of a dilatonic cosmological model are investigated. The existence of a minimum length, results in the Generalized Uncertainty Principle (GUP), which is a deformed Heisenberg algebra between the minisuperspace variables and their momenta operators. We extend these deformed commutating relations to the corresponding deformed Poisson algebra. For an exponential dilaton potential, the exact classical and quantum solutions in the commutative and noncommutative cases, and some approximate analytical solutions in the case of GUP, are presented and compared.Comment: 16 pages, 3 figures, typos correcte

New Schwarzschild-like solutions in f(T) gravity through Noether symmetries

Spherically symmetric solutions for f(T) gravity models are derived by the so called Noether Symmetry Approach. First, we present a full set of Noether symmetries for some minisuperspace models. Then, we compute analytical solutions and find that spherically symmetric solutions in f(T) gravity can be recast in terms of Schwarzschild-like solutions modified by a distortion function depending on a characteristic radius. The obtained solutions are more general than those obtained by the usual solution methods.Comment: 10 pages, to appear in Phys. Rev.

Casimir effect in a two dimensional signature changing spacetime

We study the Casimir effect for free massless scalar fields propagating on a two-dimensional cylinder with a metric that admits a change of signature from Lorentzian to Euclidean. We obtain a nonzero pressure, on the hypersurfaces of signature change, which destabilizes the signature changing region and so alters the energy spectrum of scalar fields. The modified region and spectrum, themselves, back react on the pressure. Moreover, the central term of diffeomorphism algebra of corresponding infinite conserved charges changes correspondingly.Comment: 14 pages, abstract and text extended, references added, to appear in JM

A New interpretation of MOND based on Mach principle and an Unruh like effect

A new interpretation is introduced for MOND based on the Sciama's interpretation of Mach principle and an Unruh like effect, in the context of a generalized equivalence principle. It is argued that in a locally accelerated frame with acceleration $a$ the appearance of a Rindler horizon may give rise to a constant acceleration $a_0$ as the local properties of cosmological horizon or Hubble length. The total gravitational acceleration inside this frame becomes the combination of $a$ with $a_0$. For $a\gg a_0$, the conventional gravitational mass $m_g$ interacts with the dominant acceleration as $m_g a$ and application of Sciama's interpretation leads to the standard Newtonian dynamics. For $a\ll a_0$, however, a reduced gravitational mass $\bar{m}_g$ interacts with the dominant acceleration as $\bar{m}_g a_0$ and the application of Sciama's interpretation on this reduced gravitational mass leads to MOND. This introduces a third proposal for MOND: {\it The modification of gravitational mass}.Comment: 11 pages, throughout revisio

Correspondence between Jordan-Einstein frames and Palatini-metric formalisms

We discuss the conformal symmetry between Jordan and Einstein frames considering their relations with the metric and Palatini formalisms for modified gravity. Appropriate conformal transformations are taken into account leading to the evident connection between the gravitational actions in the two mentioned frames and the Hilbert-Einstein action with a cosmological constant. We show that the apparent differences between Palatini and metric formalisms strictly depend on the representation while the number of degrees of freedom is preserved. This means that the dynamical content of both formalism is identical.Comment: 6 pages, to appear in Mod. Phys. Lett.

On Signature Transition and Compactification in Kaluza-Klein Cosmology

We consider an empty (4+1) dimensional Kaluza-Klein universe with a negative cosmological constant and a Robertson-Walker type metric. It is shown that the solutions to Einstein field equations have degenerate metric and exhibit transitioins from a Euclidean to a Lorentzian domain. We then suggest a mechanism, based on signature transition which leads to compactification of the internal space in the Lorentzian region as $a \sim |\Lambda|^{1/2}$. With the assumption of a very small value for the cosmological constant we find that the size of the universe $R$ and the internal scale factor $a$ would be related according to $Ra\sim 1$ in the Lorentzian region. The corresponding Wheeler-DeWitt equation has exact solution in the mini-superspace giving rise to a quantum state which peaks in the vicinity of the classical solutions undergoing signature transition.Comment: 13 pages, 3 figure

Motivation-based Market Segmentation in Rural Tourism: the Case of Sámán, Iran

Market segmentation is a pivotal and under-investigated issue when evaluating decision-making processes and motivational factors shaping rural tourism. The present study has examined market segmentsof rural tourists in Iran based on their sociodemographic attributes, travel characteristics and preferred leisure activities, profiling rural tourists on the base of their motivational background. The survey results indicated that rural tourism in the study area is a heterogeneous market, whose development depends on general trends in Middle East tourism market. A comprehensive knowledge of rural tourism actors may help formulating appropriate marketing strategies for internal areas destined to tourism growth

Investigation on two polymorphisms effective on HDL-C concentration in patients with coronary artery disease using restriction fragment length polymorphism

Background and aim: High density lipoprotein cholesterol (HDL-C) is a known inverse predictor of coronary heart disease (CHD). Cholesteryl ester transfer protein (CETP) and hepatic lipase (HL) are key proteins in HDL-C metabolism so that decreased CETP or HL activity is associated with high HDL-C. -629C/A polymorphism in promoter of CETP gene and-514C/T in promoter of HL gene were previously reported to reduce related protein level in plasma. In this study association of these polymorphisms with CHD related to HDL-C level were investigated. Methods: In this analytical-descriptive study 321 subjects underwent coronary angiography and divided in two groups base on angiogram (non CAD = 135 and CAD = 186). Serum lipids profile was measured by standard procedure and genotype was detected using PCR-RFLP method. Results: Overall the CETP genotype frequencies were in CAD patients: 58.8% (n=110), 28.9% (n=54) and 12.3% (n=23) and in non CAD patients: 45.2% (n=61), 41.5% (n=56) and 13.3% (n=18) for AA, CA and CC respectively. HL genotype frequencies were in CAD patients: 61.6% (n=114), 33.5% (n=62) and 4.9% (n=9) and in non CAD patients: 65.9% (n=89), 27.4% (n=37) and 6.7% (n=9) for CC, CT and TT respectively. In control group HDL-C concentration was higher for AA than CC genotype in -629C/A, and also for TT than CC genotype in -514C/T. Allele A in all subjects and T allele in woman were higher in CAD than non CAD group. A high increase in HDL-C level (10. mg/dl) was observed in individuals with CETP-AA/LIPC-TT and CETP-CA/LIPC-TT relative to CETP-CC/LIPC-CC across all subjects (P< 0.001) but there was no difference in CAD prevalence. Conclusion: Allele A from -629C/A, and T from -514C/T even with the increasing of HDL-C concentration had higher frequency in CAD than non CAD group. Therefore, it seems that HDL-C didn’t protect coronary artery when CETP or HL activity was reduced by these polymorphisms

Noncommutativity, generalized uncertainty principle and FRW cosmology

We consider the effects of noncommutativity and the generalized uncertainty principle on the FRW cosmology with a scalar field. We show that, the cosmological constant problem and removability of initial curvature singularity find natural solutions in this scenarios.Comment: 8 pages, to appear in IJT