Dynamical p-branes with a cosmological constant

We present a class of dynamical solutions in a D-dimensional gravitational theory coupled to a dilaton, a form field strength, and a cosmological constant. We find that for any D due to the presence of a cosmological constant, the metric of solutions depends on a quadratic function of the brane world volume coordinates, and the transverse space cannot be Ricci flat except for the case of 1-branes. We then discuss the dynamics of 1-branes in a D-dimensional spacetime. For a positive cosmological constant, 1-brane solutions with D>4 approach the Milne universe in the far-brane region. On the other hand, for a negative cosmological constant, each 1-brane approaches the others as the time evolves from a positive value, but no brane collision occurs for D>4, since the spacetime close to the 1-branes eventually splits into the separate domains. In contrast, the D=3 case provides an example of colliding 1-branes. Finally, we discuss the dynamics of 0-branes and show that for D>2, they behave like the Milne universe after the infinite cosmic time has passed.Comment: 21 pages, 7 figures; v2: minor correction

Towards the Classification of Non-Marginal Bound States of M-branes and Their Construction Rules

We present a systematic analysis of possible bound states of M-brane solutions (including waves and monopoles) by using the solution generating technique of reduction of M-brane to 10 dimensions, use of T-duality and then lifting back to 11 dimensions. We summarize a list of bound states for one- and two-charge cases including tilted brane solutions. Construction rules for these non-marginal solutions are also discussed.Comment: Latex, 37 page

Holography and D3-branes in Melvin Universes

Recently,in a paper hep-th/0511197, it was found that non-commutative super Yang-Mills (NCSYM) theory with space-dependent noncommutativity can be formulated as a decoupling limit of open strings ending on D3-branes wrapping a Melvin universe supported by a flux of the NSNS B-field. Under S-duality, we show that this theory turns into a noncommutative open string (NCOS) theory with space-dependent space-time noncommutativity and effective space-dependent string scale. It is an NCOS theory with both space-dependent space-space and space-time noncommutativities under more general $SL(2,\mathbb{Z})$ transformation. These space-dependent noncommutative theories (NCSYM and NCOS) have completely the same thermodynamics as that of ordinary super YM theory, NCSYM and NCOS theories with constant noncommutativity in the dual supergravity description. Starting from black D3-brane solution in the Melvin universe and making a Lorentz boost along one of spatial directions on the worldvolume of D3-branes, we show that the decoupled theory is a light-like NCSYM theory with space-dependent noncommutativity in a static frame or in an infinite-momentum frame depending on whether there is a gravitational pp-wave on the worldvolume of the D3-branes.Comment: Latex, 13 pages, v2: typos fixed, the version in PR

Probing the Coupling between Dark Components of the Universe

We place observational constraints on a coupling between dark energy and dark matter by using 71 Type Ia supernovae (SNe Ia) from the first year of the five-year Supernova Legacy Survey (SNLS), the cosmic microwave background (CMB) shift parameter from the three-year Wilkinson Microwave Anisotropy Probe (WMAP), and the baryon acoustic oscillation (BAO) peak found in the Sloan Digital Sky Survey (SDSS). The interactions we study are (i) constant coupling delta and (ii) varying coupling delta(z) that depends on a redshift z, both of which have simple parametrizations of the Hubble parameter to confront with observational data. We find that the combination of the three databases marginalized over a present dark energy density gives stringent constraints on the coupling, -0.08 < delta < 0.03 (95% CL) in the constant coupling model and -0.4 < delta_0 < 0.1 (95% CL) in the varying coupling model, where delta_0 is a present value. The uncoupled LambdaCDM model (w_X = -1 and delta = 0) still remains a good fit to the data, but the negative coupling (delta < 0) with the equation of state of dark energy w_X < -1 is slightly favoured over the LambdaCDM model.Comment: 9 pages, 7 figures, RevTeX, minor corrections, references added, accepted for publication in Phys. Rev.

Supersymmetric Rotating Black Hole in a Compactified Spacetime

We construct a supersymmetric rotating black hole with asymptotically flat four-dimensional spacetime times a circle, by superposing an infinite number of BMPV black hole solutions at the same distance in one direction. The near horizon structure is the same as that of the five-dimensional BMPV black hole. The rotation of this black hole can exceed the Kerr bound in general relativity ($q\equiv a/G_4 M=1$), if the size is small.Comment: 7 pages, 3 figures; v2: comparison with black ring removed, detailed discussion of rotation added, refs. added, v3: minor corrections, version to appear in PR

Cluster Mass Estimate and a Cusp of the Mass Density Distribution in Clusters of Galaxies

We study density cusps in the center of clusters of galaxies to reconcile X-ray mass estimates with gravitational lensing masses. For various mass density models with cusps we compute X-ray surface brightness distribution, and fit them to observations to measure the range of parameters in the density models. The Einstein radii estimated from these density models are compared with Einstein radii derived from the observed arcs for Abell 2163, Abell 2218, and RX J1347.5-1145. The X-ray masses and lensing masses corresponding to these Einstein radii are also compared. While steeper cusps give smaller ratios of lensing mass to X-ray mass, the X-ray surface brightnesses estimated from flatter cusps are better fits to the observations. For Abell 2163 and Abell 2218, although the isothermal sphere with a finite core cannot produce giant arc images, a density model with a central cusp can produce a finite Einstein radius, which is smaller than the observed radii. We find that a total mass density profile which declines as $\sim r^{-1.4}$ produces the largest radius in models which are consistent with the X-ray surface brightness profile. As the result, the extremely large ratio of the lensing mass to the X-ray mass is improved from 2.2 to 1.4 for Abell 2163, and from 3 to 2.4 for Abell 2218. For RX J1347.5-1145, which is a cooling flow cluster, we cannot reduce the mass discrepancy.Comment: 23 pages, 10 figures, Latex, uses aasms4.sty, accepted for publication in ApJ, Part

Parent Actions, Dualities and New Weyl-invariant Actions of Bosonic p-branes

By using the systematic approach of parent action method, we derive one Weyl-noninvariant and two Weyl-invariant actions of bosonic $p$-branes ($p\geq 2$) starting from the Nambu-Goto action, and establish the duality symmetries in this set of four actions. Moreover, we discover a new bosonic $p$-brane action (including the string theory) and deduce two corresponding Weyl-invariant formulations by proposing a new special parent action. We find that the same duality symmetries as those mentioned above exist in this new set of actions. The new $p$-brane actions are also briefly analyzed.Comment: 19 pages, 14 figures. The first section is modified slightly, and references are adde

The Effect of Fe-Al Substitution on the Crystal Structure of MgSiO3 Bridgmanite

The crystal chemistry of ten well-characterized bridgmanite single-crystals with Fe and Al contents ranging from 0 to 0.40 atoms per two-cation formula units were investigated by single-crystal X-ray diffraction. Structural refinements indicate that Fe3+ and Al mainly occupy the Mg and Si sites, respectively, when present in similar proportions. Molar volumes of bridgmanite endmember components were refined using data from this and previous studies and found to decrease in the order Fe3+Fe3+O3 > MgFe3+O2.5 > Fe3+AlO3 > MgAlO2.5 > AlAlO3 > Fe2+SiO3 > MgSiO3. Fe3+AlO3 charge-coupled substitution leads to an anisotropic increase of B-O bond distances, resulting in more distorted octahedral B sites and in a more significant increase of the c-axis with respect to the a- and b-axes. Valence bond calculations indicate that the A site is more compressible than the B site for all bridgmanite samples studied, implying that octahedral tilting and distortion will dominate the bridgmanite compression mechanism. Guided by these crystal chemical observations, bulk moduli of bridgmanite endmember components were estimated using results of previous studies. The volume changes of equilibria controlling the speciation of bridgmanite components were then calculated at conditions relevant to the top of Earth's lower mantle. The proportion of oxygen vacancy components is predicted to decrease with pressure. While the stability of the bridgmanite Fe3+AlO3 component will drive charge disproportionation to produce iron metal at the top of the lower mantle, this appears to be much less favorable by 50 GPa. An increase in the proportion of the Fe3+Fe3+O3 bridgmanite component, however, may favor the formation of iron metal at higher pressures

The BRST Operator for the Large N=4N=4 Superconformal Algebra

We review the detailed structure of the large $N=4$ superconformal algebra, and construct its BRST operator which constitutes the main object for analyzing $N=4$ strings. We then derive the general condition for the nilpotency of the BRST operator and show that there exists a line of critical $N=4$ string theories.Comment: Latex file, 16 pages, NBI-HE-94-1