Gravitational Redshift in Einstein-Kalb-Ramond Spacetime and Randall-Sundrum Scenario

It is shown that the gravitational redshift as predicted by Einstein's theory, is modified in presence of second rank antisymmetric tensor (Kalb-Ramond) field in a string inspired background spacetime.In presence of extra dimensions, the Randall-Sundrum brane world scenario is found to play a crucial role in suppressing this additional shift. The bound on the value of the warp factor is determined from the redshift data and is found to be in good agreement with that determined from the requirements of Standard model.Comment: 4 Pages, Revtex, No figures, version thoroughly revise

Charged black holes in generalized dilaton-axion gravity

We study generic Einstein-Maxwell-Kalb-Ramond-dilaton actions, and derive conditions under which they give rise to static, spherically symmetric black hole solutions. We obtain new asymptotically flat and non-flat black hole solutions which are in general electrically and magnetically charged. They have positive definite and finite quasi-local masses. Existing non-rotating black hole solutions (including those appearing in low energy string theory) are recovered in special limits.Comment: Replaced with revised version, 33 pages, No figure

Modulus stabilization of generalized Randall Sundrum model with bulk scalar field

We study the stabilization of inter-brane spacing modulus of generalized warped brane models with a nonzero brane cosmological constant. Employing Goldberger-Wise stabilization prescription of brane world models with a bulk scalar field, we show that the stabilized value of the modulus generally depends on the value of the brane cosmological constant. Our result further reveals that the stabilized modulus value corresponding to a vanishingly small cosmological constant can only resolve the gauge hierarchy problem simultaneously. This in turn vindicates the original Randall-Sundrum model where the 3-brane cosmological constant was chosen to be zero.Comment: 12 Pages, 1 figure, Revtex, Version to appear in Euro. Phys. Let

Cosmic Dynamics in the Chameleon Cosmology

We study in this paper chameleon cosmology applied to Friedmann-Robertson-Walker space, which gives rise to the equation of state (EoS) parameter larger than -1 in the past and less than -1 today, satisfying current observations. We also study cosmological constraints on the model using the time evolution of the cosmological redshift of distant sources which directly probes the expansion history of the universe. Due to the evolution of the universe's expansion rate, the model independent Cosmological Redshift Drift (CRD)test is expected to experience a small, systematic drift as a function of time. The model is supported by the observational data obtained from the test.Comment: 16 pages, 9 figure

The proton Nuclear Magnetic Resonance spin-lattice relaxation rate of some hydrated synthetic and natural sands

The proton nuclear magnetic resonance (NMR) spin-lattice relaxation rate (R1) of hydrated sands is often used to determine porosity characteristics of near-surface aquifers using magnetic resonance sounding. Large variations in R1 have been reported in laboratory measurements on hydrated sands. To understand these variations, the R1 values of several fully hydrated sands were studied as a function of grain diameter (d) and magnetic field strength (BB0). We conclude the variations are a consequence of trace paramagnetic metals in the sand grains. R1 values from magnetic resonance sounding data should not be used to predict void size in aquifers unless the exact chemical composition of the grains is known

Electric quadrupole moment of the 5d2D3/25d^2 D_{3/2} state in 171Yb+^{171}Yb^+ : A relativistic coupled-cluster analysis

The electric quadrupole moment for the $5d^{2}D_{3/2}$ state of $\mathrm{^{171}Yb^{+}}$, has been calculated using the relativistic coupled-cluster method. Earlier a similar calculation was performed for the 4d $^2D_{5/2}$ state of $\mathrm{^{88}Sr^{+}}$ which is the most accurate determination to date {[}PRL, \textbf{96}, 193001 (2006)]. The present calculation of the electric quadrupole moment of $\mathrm{^{171}Yb^{+}}$ yielded a value $2.157 ea_{0}^{2}$ where the experimental value is $2.08(11)ea_{0}^{2}$; $a_{0}$ is the Bohr radius and $e$ the elementary charge. We discuss in this paper our results in detail for $^{171}{\rm Yb}^{+}$ and highlight the dominant correlation effects present. We have presented the effect of inner core excitations and their contribution to the electric quadrupole moment, which is a property sensitive to regions away from the nucleus.Comment: 5 pages, 1 figure. Accepted in Phys.Rev.

Crossing the phantom divide with k-essence in brane-worlds

We study a flat 3-brane in presence of a linear $k$ field with nonzero cosmological constant $\Lambda_{4}$. In this model the crossing of the phantom divide (PD) occurs when the $k$-essence energy density becomes negative. We show that in the high energy regime the effective equation of state has a resemblance of a modified Chaplygin gas while in the low energy regime it becomes linear. We find a scale factor that begins from a singularity and evolves to a de Sitter stable stage while other solutions have a super-accelerated regime and end with a big rip. We use the energy conditions to show when the effective equation of state of the brane-universe crosses the PD.Comment: 8 pages, 5 figures. The article was fully rewritten. References added. Accepted for publication in MPLA (2010

Impurity spin relaxation in S=1/2 XX chains

Dynamic autocorrelations $$ (\alpha=x,z) of an isolated impurity spin in a S=1/2 XX chain are calculated. The impurity spin, defined by a local change in the nearest-neighbor coupling, is either in the bulk or at the boundary of the open-ended chain. The exact numerical calculation of the correlations employs the Jordan-Wigner mapping from spin operators to Fermi operators; effects of finite system size can be eliminated. Two distinct temperature regimes are observed in the long-time asymptotic behavior. At T=0 only power laws are present. At high T the x correlation decays exponentially (except at short times) while the z correlation still shows an asymptotic power law (different from the one at T=0) after an intermediate exponential phase. The boundary impurity correlations follow power laws at all T. The power laws for the z correlation and the boundary correlations can be deduced from the impurity-induced changes in the properties of the Jordan-Wigner fermion states.Comment: Final version to be published in Phys. Rev. B. Three references added, extended discussion of relation to previous wor

Disrupted in schizophrenia 1 (DISC1) L100P mutants have impaired activity-dependent plasticity in vivo and in vitro

Major neuropsychiatric disorders are genetically complex but share overlapping etiology. Mice mutant for rare, highly penetrant risk variants can be useful in dissecting the molecular mechanisms involved. The gene disrupted in schizophrenia 1 (DISC1) has been associated with increased risk for neuropsychiatric conditions. Mice mutant for Disc1 display morphological, functional and behavioral deficits that are consistent with impairments observed across these disorders. Here we report that Disc1 L100P mutants are less able to reorganize cortical circuitry in response to stimulation in vivo. Molecular analysis reveals that the mutants have a reduced expression of PSD95 and pCREB in visual cortex and fail to adjust expression of such markers in response to altered stimulation. In vitro analysis shows that mutants have impaired functional reorganization of cortical neurons in response to selected forms of neuronal stimulation, but there is no altered basal expression of synaptic markers. These findings suggest that DISC1 has a critical role in the reorganization of cortical plasticity and that this phenotype becomes evident only under challenge, even at early postnatal stages. This result may represent an important etiological mechanism in the emergence of neuropsychiatric disorders

Growth rate of small-scale dynamo at low magnetic Prandtl numbers

In this study we discuss two key issues related to a small-scale dynamo instability at low magnetic Prandtl numbers and large magnetic Reynolds numbers, namely: (i) the scaling for the growth rate of small-scale dynamo instability in the vicinity of the dynamo threshold; (ii) the existence of the Golitsyn spectrum of magnetic fluctuations in small-scale dynamos. There are two different asymptotics for the small-scale dynamo growth rate: in the vicinity of the threshold of the excitation of the small-scale dynamo instability, $\lambda \propto \ln({\rm Rm}/ {\rm Rm}^{\rm cr})$, and when the magnetic Reynolds number is much larger than the threshold of the excitation of the small-scale dynamo instability, $\lambda \propto {\rm Rm}^{1/2}$, where ${\rm Rm}^{\rm cr}$ is the small-scale dynamo instability threshold in the magnetic Reynolds number ${\rm Rm}$. We demonstrated that the existence of the Golitsyn spectrum of magnetic fluctuations requires a finite correlation time of the random velocity field. On the other hand, the influence of the Golitsyn spectrum on the small-scale dynamo instability is minor. This is the reason why it is so difficult to observe this spectrum in direct numerical simulations for the small-scale dynamo with low magnetic Prandtl numbers.Comment: 14 pages, 1 figure, revised versio