Possible Molecular States of Ds∗Dˉs∗D^{*}_s\bar{D}^{*}_s System and Y(4140)

The interpretation of Y(4140) as a $D^{*}_s\bar{D}^{*}_s$ molecule is studied dynamically in the one boson exchange approach, where $\sigma$, $\eta$ and $\phi$ exchange are included. Ten allowed $D^{*}_s\bar{D}^{*}_s$ states with low spin parity are considered, we find that the $J^{PC}=0^{++}$, $1^{+-}$, $0^{-+}$, $2^{++}$ and $1^{--}$ $D^{*}_s\bar{D}^{*}_s$ configurations are most tightly bound. We suggest the most favorable quantum numbers are $J^{PC}=0^{++}$ for Y(4140) as a $D^{*}_s\bar{D}^{*}_s$ molecule, however, $J^{PC}=0^{-+}$ and $2^{++}$ can not be excluded. We propose to search for the $1^{+-}$ and $1^{--}$ partners in the $J/\psi\eta$ and $J/\psi\eta'$ final states, which is an important test of the molecular hypothesis of Y(4140) and the reasonability of our model. The $0^{++}$ $B^{*}_s\bar{B}^{*}_s$ molecule is deeply bound, experimental search in the $\Upsilon(1S)\phi$ channel at Tevatron and LHC is suggested.Comment: 13 pages,2 figure

On supergravity solutions of space-like Dp-branes

Recently the time dependent solutions of type II supergravities in $d = 10$, with the metric having the symmetry $ISO(p+1) \times SO(8-p, 1)$ have been given by two groups (Chen-Gal'tsov-Gutperle (CGG), [hep-th/0204071] and Kruczenski-Myers-Peet (KMP), [hep-th/0204144]). The supergravity solutions correspond to space-like D$p$-branes in type II string theory. While the CGG solution is a four parameter solution, the KMP solution is a three parameter solution and so in general they are different. This difference can be attributed to the fact that unlike the CGG solution, KMP uses a specific boundary condition for the metric and the dilaton field. It is shown that when we impose the boundary conditions used in the KMP solution to the CGG solution then both become three parameter solutions and they map to each other under a coordinate transformation along with a Hodge duality of the field strength. We also give the relations between the parameters characterizing the two solutions.Comment: 14 pages, LaTeX, v2: minor corrections and a reference adde

The geometry of null rotation identifications

The geometry of flat spacetime modded out by a null rotation (boost+rotation) is analysed. When embedding this quotient spacetime in String/M-theory, it still preserves one half of the original supersymmetries. Its connection with the BTZ black hole, supersymmetric dilatonic waves and one possible resolution of its singularity in terms of nullbranes are also discussed.Comment: 1+18 pages, 5 figures. v2 references adde

Properties of Interfaces in the two and three dimensional Ising Model

To investigate order-order interfaces, we perform multimagnetical Monte Carlo simulations of the $2D$ and $3D$ Ising model. Following Binder we extract the interfacial free energy from the infinite volume limit of the magnetic probability density. Stringent tests of the numerical methods are performed by reproducing with high precision exact $2D$ results. In the physically more interesting $3D$ case we estimate the amplitude $F^s_0$ of the critical interfacial tension $F^s = F^s_0 t^\mu$ to be $F^s_0 = 1.52 \pm 0.05$. This result is in good agreement with a previous MC calculation by Mon, as well as with experimental results for related amplitude ratios. In addition, we study in some details the shape of the magnetic probability density for temperatures below the Curie point.Comment: 25 pages; sorry no figures include

Null Brane Intersections

We study pairs of planar D-branes intersecting on null hypersurfaces, and other related configurations. These are supersymmetric and have finite energy density. They provide open-string analogues of the parabolic orbifold and null-fluxbrane backgrounds for closed superstrings. We derive the spectrum of open strings, showing in particular that if the D-branes are shifted in a spectator dimension so that they do not intersect, the open strings joining them have no asymptotic states. As a result, a single non-BPS excitation can in this case catalyze a condensation of massless modes, changing significantly the underlying supersymmetric vacuum state. We argue that a similar phenomenon can modify the null cosmological singularity of the time-dependent orbifolds. This is a stringy mechanism, distinct from black-hole formation and other strong gravitational instabilities, and one that should dominate at weak string coupling. A by-product of our analysis is a new understanding of the appearance of 1/4 BPS threshold bound states, at special points in the moduli space of toroidally-compactified type-II string theory.Comment: Tex file, uses harvmac, 24 pages with 5 figures. Corrected typos and added references. Final version to appear in JHE

Removing Singularities

Big bang/crunch curvature singularities in exact CFT string backgrounds can be removed by turning on gauge fields. This is described within a family of {SL(2)xSU(2)xU(1)_x}/{U(1)xU(1)} quotient CFTs. Uncharged incoming wavefunctions from the ``whiskers'' of the extended universe can be fully reflected if and only if a big bang/crunch curvature singularity, from which they are scattered, exists. Extended BTZ-like singularities remain as long as U(1)_x is compact.Comment: 21 pages, harvma

X(3872) and Other Possible Heavy Molecular States

We perform a systematic study of the possible molecular states composed of a pair of heavy mesons such as $D\bar D$, $D^\ast\bar D$, $D^\ast \bar D^\ast$ in the framework of the meson exchange model. The exchanged mesons include the pseudoscalar, scalar and vector mesons. Through our investigation, we find that (1) the structure X(3764) is not a molecular state; (2) There exists strong attraction in the range $r < 1$ fm for the $D^*\bar D^*$ system with $J=0, 1$. If future experiments confirm $Z^+(4051)$ as a loosely bound molecular state, its quantum number is probably $J^{P}=0^+$. Its partner state $\Phi^{**0}$ may be searched for in the $\pi^0\chi_{c1}$ channel; (3) The vector meson exchange provides strong attraction in the $D^\ast \bar D$ channel together with the pion exchange. A bound state solution exists with a reasonable cutoff parameter $\Lambda\sim 1.4$ GeV. X(3872) may be accommodated as a molecular state dynamically although drawing a very definite conclusion needs further investigation; (4) The $B^\ast \bar B$ molecular state exists.Comment: 21 pages, 17 tables, 11 figures. Typos correcte

Non-Commutative Instantons and the Seiberg-Witten Map

We present several results concerning non-commutative instantons and the Seiberg-Witten map. Using a simple ansatz we find a large new class of instanton solutions in arbitrary even dimensional non-commutative Yang-Mills theory. These include the two dimensional ``shift operator'' solutions and the four dimensional Nekrasov-Schwarz instantons as special cases. We also study how the Seiberg-Witten map acts on these instanton solutions. The infinitesimal Seiberg-Witten map is shown to take a very simple form in operator language, and this result is used to give a commutative description of non-commutative instantons. The instanton is found to be singular in commutative variables.Comment: 26 pages, AMS-LaTeX. v2: the formula for the commutative description of the Nekrasov-Schwarz instanton corrected (sec. 4). v3: minor correction

The molecular systems composed of the charmed mesons in the HSˉ+h.c.H\bar{S}+h.c. doublet

We study the possible heavy molecular states composed of a pair of charm mesons in the H and S doublets. Since the P-wave charm-strange mesons $D_{s0}(2317)$ and $D_{s1}(2460)$ are extremely narrow, the future experimental observation of the possible heavy molecular states composed of $D_s/D_s^\ast$ and $D_{s0}(2317)/D_{s1}(2460)$ may be feasible if they really exist. Especially the possible $J^{PC}=1^{--}$ states may be searched for via the initial state radiation technique.Comment: 42 pages, 4 tables, 31 figures. Improved numerical results and Corrected typos

On the instability of 3d null singularities

String propagation on a three-dimensional Lorentzian string orbifold with a null singularity has been studied by Horowitz and Steif, and more recently by Liu, Moore and Seiberg. We analyze the target space as a classical gravitational background. The singularity becomes spacelike when an arbitrarily small amount of matter is thrown at the singularity. This can be seen directly by studying the null singularity as a limit of the M=0, J=0 BTZ black hole metric.Comment: 9 pages, uses harvmac.tex. v2: minor wording changes in introduction, fixed reference typo, new reference