From pub_off@ictp.trieste.it Wed Sep 13 21:00:48 2000 Date: Tue, 12 Sep 2000 09:47:12 +0200 From: Publications OfficeTo: preprints@ictp.trieste.it Subject: 6th List of 2000 ICTP Preprints +---------------------- "ICTP SCIENTIFIC PREPRINTS LIST" ------------------+ | Automatic e-mail delivery service of recent ICTP Preprints Titles | | SOURCES can be retrieved from URL: http://www.ictp.trieste.it/~pub_off | HARD COPIES are available by e-mail request to: pub_off@ictp.trieste.it | by quoting the ICTP preprint number and giving your full postal address +--------------------------------------------------------------------------+ 2000LIST-6 This is the sixth list of 2000 ICTP preprints which are available. +--------------------------------------------------------------+ ICTP Preprint No.IC2000062 A SELF-TUNING EXACT SOLUTION AND THE NON-EXISTENCE OF HORIZONS IN 5d GRAVITY-SCALAR SYSTEM by Chuan-Jie Zhu ABSTRACT: We present an exact thick domain wall solution with naked singularities to five dimensional gravity coupled with a scalar field with exponential potential. In our solution we found exactly the special coefficient of the exponent as coming from compactification of string theory with cosmological constant. We show that this solution is self-tuning when a 3-brane is included. In searching for a solution with horizon we found a similar exact solution with fine-tuned exponent coefficient with an integration constant. Failing to find a solution with horizon we prove the non-existence of horizons. These naked singularities actually can't be resolved by horizon. We also comment on the physical relevance of this solution. ICTP Preprint No.IC2000065 NEUTRINO MASSES AND THE GLUINO AXION MODEL by D.A. Demir, Ernest Ma and Utpal Sarkar ABSTRACT: We extend the recently proposed gluino axion model to include neutrino masses. We discuss how the canonical seesaw model and the Higgs triplet model may be realized in this framework. In the former case, the heavy singlet neutrinos are contained in superfields which do not have any vacuum expectation value, whereas the gluino axion is contained in one which does. We also construct a specific renormalizable model which realizes the mass scale relationship $M_{SUSY} \sim f_a^2/M_U$, where $f_a$ is the axion decay constant and $M_U$ is a large effective mass parameter. ICTP Preprint No.IC2000068 HARMONIC SPINORS OF DIRAC OPERATOR OF CONNECTION WITH TORSION IN DIMENSION 4 by Peter Dalakov and Stefan Ivanov ABSTRACT: It is shown that the existence of parallel (-)-spinor with respect to a metric connection with totally skew-symmetric torsion requires more local restriction than the existence of parallel (+)-spinor. It is proved that every harmonic spinor with respect to the Dirac operator of this connection on a compact four dimensional spin Riemannian manifold is parallel with respect to a naturally arising metric connection with totally skew-symmetric torsion and all these spaces are classified up to a conformal transformations. ICTP Preprint No.IC2000070 INCREASING RELIABILITY OF GAUSS-KRONROD QUADRATURE BY ERATOSTHENES' SIEVE METHOD by Gh. Adam and S. Adam ABSTRACT: The reliability of the local error estimates returned by the Gauss-Kronrod quadrature rules can be raised up to the theoretical 100\% rate of success, under error estimate sharpening, provided a number of natural validating conditions are required. The self-validating scheme of the local error estimates, which is easy to implement and adds little supplementary computing effort, strengthens considerably the correctness of the decisions within the automatic adaptive quadrature. ICTP Preprint No.IC2000071 THE SHORT DISTANCE CONTRIBUTION TO THE $B_{s}\rightarrow\gamma\gamma$ DECAY IN THE SM AND MSSM by G.G. Devidze ABSTRACT: The complete calculation of the short distance contributions to the $B_{s}\rightarrow\gamma\gamma$ decay in the SM and MSSM are presented. The branching ratio and relative part of CP-even state of final photons are calculated. The branching ratio and relative part of CP-even state of final photons in the MSSM maybe significantly larger than the standard model estimate. ICTP Preprint No.IC2000072 LOGARITHMIC CORRECTIONS FROM FERROMAGNETIC IMPURITY ENDING BONDS OF OPEN ANTIFERROMAGNETIC HOST CHAINS by Jizhong Lou, Jianhui Dai, Shaojin Qin, Zhaobin Su and Lu Yu ABSTRACT: We analyze the logarithmic corrections due to ferromagnetic impurity ending bonds of open spin 1/2 antiferromagnetic chains, using the density matrix renormalization group technique. A universal finite size scaling $\sim {\frac 1 {L \log L }}$ for impurity contributions in the quasi-degenerate ground state energy is demonstrated for a zigzag spin 1/2 chain at the critical next nearest neighbor coupling and the standard Heisenberg spin 1/2 chain, in the long chain limit. Using an exact solution for the latter case it is argued that one can extract the impurity contributions to the entropy and specific heat from the scaling analysis. It is also shown that a pure spin $3/2$ open Heisenberg chain belongs to the same universality class. ICTP Preprint No.IC2000073 ON NONCOMMUTATIVE OPEN STRING THEORIES by J.G. Russo and M.M. Sheikh-Jabbari ABSTRACT: We investigate new compactifications of OM theory giving rise to a 3+1 dimensional open string theory with noncommutative $x^0$-$x^1$ and $x^2$-$x^3$ coordinates. The theory can be directly obtained by starting with a D3 brane with parallel (near critical) electric and magnetic field components, in the presence of a RR scalar field. The magnetic parameter permits to interpolate continuously between the $x^0$-$x^1$ noncommutative open string theory and the $x^2$-$x^3$ spatial noncommutative $U(N)$ super Yang-Mills theory. We discuss $SL(2,Z)$ transformations of this theory. Using the supergravity description of the large $N$ limit, we also compute corrections to the quark-antiquark Coulomb potential arising in the NCOS theory. ICTP Preprint No.IC2000074 STABLE Q-BALLS FROM EXTRA DIMENSIONS by D.A. Demir ABSTRACT: Given a bulk scalar field with sufficient self-interactions in a higher dimensional spacetime, it is shown that the continuous symmetries in four dimensions, induced by the topological structure of the compact manifold, naturally lead to formation of stable nontopological solitons of Q-ball type. The mass per unit charge inside the soliton is bounded by the size of the extra dimensions, and it is thus stable with respect to decaying into excited levels of all bulk fields, irrespective of their bulk masses. A familiar example is the Standard Model in the bulk, where the Kaluza-Klein levels of the Higgs boson form a stable Q-ball. These stable solitons are natural candidates for the dark matter in the Universe. ICTP Preprint No.IC2000075 HOLOGRAPHY IN AN EARLY UNIVERSE WITH ASYMMETRIC INFLATION by Elcio Abdalla and L. Alejandro Correa-Borbonet ABSTRACT: We discuss the validity of the holographic principle in a $(4+n)$ dimensional universe in an asymmetric inflationary phase. ICTP Preprint No.IC2000081 EFFECTS OF DIRECTIONAL SUBDIVIDING ON ADAPTIVE GRID EMBEDDING by E. Shirani and M. Ameri ABSTRACT: The effects of directionally subdivided adaptive grid-embedded on the computational time and space are considered. Euler equations are used to solve transonic and supersonic flows in a bicircular arc and supersonic flow in a converging channel. The effects of using non-directional and directional subdividing on adaptive grid embedding on the computational time and the number of grid points required for the same accuracy are considered. To avoid the problem of unstructured grid, the semi-structured grid was used. In this work, multi-grid technique is applied to increase the convergence rate. The results show that for the same accuracy, the number of grid points and the computational time are considerably decreased. When the multiple-grid is used, the computational time is reduced by up to a factor of two. This factor varies due to the flow properties and geometry. When directional subdividing is used, the number of grid points is reduced by a factor of about five, compared to fine uniform grid calculations and by factor of 1.5, compared to the non- directional subdividing case. The computational time is reduced to about one tenth of the CPU time required for non-adapted grid scheme. | +--------------------------------------------------------------------------+ | To SUBSCRIBE/UNSUBSCRIBE from this service send an e-mail | To: preprints-request@ictp.trieste.it | Subject: (LEAVE IT EMPTY) | and write in the body of the message | ^^^^^^^^^^^ | SUBSCRIBE your_email_address or | UNSUBSCRIBE your_email_address | depending on your choice (FOR EXAMPLE: subscribe john@ictp.trieste.it) +--------------------------------------------------------------------------+