Instanton calculus in R-R background and the topological string

We study a system of fractional D3 and D(-1) branes in a Ramond-Ramond closed string background and show that it describes the gauge instantons of N=2 super Yang-Mills theory and their interactions with the graviphoton of N=2 supergravity. In particular, we analyze the instanton moduli space using string theory methods and compute the prepotential of the effective gauge theory exploiting the localization methods of the instanton calculus showing that this leads to the same information given by the topological string. We also comment on the relation between our approach and the so-called Omega-background.Comment: 38 pages, 2 figures, JHEP class (included); final version to be pubished in JHE

Non-perturbative contributions to the plane-wave string mass matrix

D-instanton contributions to the mass matrix of arbitrary excited string states of type IIB string theory in the maximally supersymmetric plane-wave background are calculated to leading order in the string coupling using a supersymmetric light-cone boundary state formalism. The explicit non-perturbative dependence of the mass matrix on the complex string coupling, the plane-wave mass parameter and the mode numbers of the excited states is determined.Comment: 25 pages, 1 figure. v3: corrected minor typos, added referenc

Dense circumnuclear molecular gas in starburst galaxies

We present results from a study of the dense circumnuclear molecular gas of starburst galaxies. The study aims to investigate the interplay between starbursts, active galactic nuclei and molecular gas.We characterize the dense gas traced by HCN, HCO and HNC and examine its kinematics in the circumnuclear regions of nine starburst galaxies observed with the Australia Telescope Compact Array. We detect HCN (1-0) and HCO (1-0) in seven of the nine galaxies and HNC (1-0) in four. Approximately 7 arcsec resolution maps of the circumnuclear molecular gas are presented. The velocity-integrated intensity ratios, HCO (1-0)/HCN (1-0) and HNC (1-0)/HCN (1-0), are calculated. Using these integrated intensity ratios and spatial intensity ratio maps, we identify photon-dominated regions (PDRs) in NGC 1097, NGC 1365 and NGC 1808. We find no galaxy which shows the PDR signature in only one part of the observed nuclear region.We also observe unusually strong HNC emission in NGC 5236, but it is not strong enough to be consistent with X-ray-dominated region chemistry. Rotation curves are derived for five of the galaxies and dynamical mass estimates of the inner regions of three of the galaxies are made. © 2016 The Authors.This project was supported by the Brother Vincent Cotter Award for Physics (UNSW). LVM has been supported by Grant AYA2011-30491-C02-01 co-financed by MICINN and FEDER funds, and the Junta de Andalucia (Spain) grants P08-FQM-4205 and TIC-114. WAB acknowledges the support as a Visiting Professor of the Chinese Academy of Sciences (KJZD-EW-T01). The research leading to these results has received funding from the European Community's Seventh Framework Programme (/FP7/2007-2013/) under grant agreement No 229517.Peer Reviewe

Mersenne Primes, Polygonal Anomalies and String Theory Classification

It is pointed out that the Mersenne primes $M_p=(2^p-1)$ and associated perfect numbers ${\cal M}_p=2^{p-1}M_p$ play a significant role in string theory; this observation may suggest a classification of consistent string theories.Comment: 10 pages LaTe

Orientifolds of Gepner Models

We systematically construct and study Type II Orientifolds based on Gepner models which have N=1 supersymmetry in 3+1 dimensions. We classify the parity symmetries and construct the crosscap states. We write down the conditions that a configuration of rational branes must satisfy for consistency (tadpole cancellation and rank constraints) and spacetime supersymmetry. For certain cases, including Type IIB orientifolds of the quintic and a two parameter model, one can find all solutions in this class. Depending on the parity, the number of vacua can be large, of the order of 10^{10}-10^{13}. For other models, it is hard to find all solutions but special solutions can be found -- some of them are chiral. We also make comparison with the large volume regime and obtain a perfect match. Through this study, we find a number of new features of Type II orientifolds, including the structure of moduli space and the change in the type of O-planes under navigation through non-geometric phases.Comment: 142 page

Regulation, sensory domains and roles of two Desulfovibrio desulfuricans ATCC27774 Crp family transcription factors, HcpR1 and HcpR2, in response to nitrosative stress

In silico analyses identified a Crp/Fnr family transcription factor (HcpR) in sulfate-reducing bacteria that controls expression of the hcp gene, which encodes the hybrid cluster protein and contributes to nitrosative stress responses. There is only one hcpR gene in the model sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough, but two copies in D. desulfuricans 27774, which can use nitrate as an alternative electron acceptor to sulfate. Structures of the D. desulfuricans hcpR1, hcpR2 and hcp operons are reported. We present evidence that hcp expression is regulated by HcpR2, not by HcpR1, and that these two regulators differ in both their DNA-binding site specificity and their sensory domains. HcpR1 is predicted to be a b-type cytochrome. HcpR1 binds upstream of the hcpR1 operon and its synthesis is regulated coordinately with hcp in response to NO. In contrast, hcpR2 expression was not induced by nitrate, nitrite or NO. HcpR2 is an iron-sulfur protein that reacts with NO and O2 . We propose that HcpR1 and HcpR2 use different sensory mechanisms to regulate subsets of genes required for defense against NO-induced nitrosative stress, and that diversification of signal perception and DNA recognition by these two proteins is a product of D. desulfuricans adaptation to its particular environmental niche. This article is protected by copyright. All rights reserved

The Stochastic Dynamics of an Array of Atomic Force Microscopes in a Viscous Fluid

We consider the stochastic dynamics of an array of two closely spaced atomic force microscope cantilevers in a viscous fluid for use as a possible biomolecule sensor. The cantilevers are not driven externally, as is common in applications of atomic force microscopy, and we explore the stochastic cantilever dynamics due to the constant buffeting of fluid particles by Brownian motion. The stochastic dynamics of two adjacent cantilevers are correlated due to long range effects of the viscous fluid. Using a recently proposed thermodynamic approach the hydrodynamic correlations are quantified for precise experimental conditions through deterministic numerical simulations. Results are presented for an array of two readily available atomic force microscope cantilevers. It is shown that the force on a cantilever due to the fluid correlations with an adjacent cantilever is more than 3 times smaller than the Brownian force on an individual cantilever. Our results indicate that measurements of the correlations in the displacement of an array of atomic force microscopes can detect piconewton forces with microsecond time resolution.Comment: 7 page article with 11 images submitted to the International Journal of Nonlinear Mechanic

Expanded Strings in the Background of NS5-branes via a M2-brane, a D2-brane and D0-branes

Classical configurations of a M2-brane, a D2-brane and D0-branes are investigated in the background of an infinite array of M5-branes or NS5-branes. On the M2-brane, we discuss three kinds of configurations, such as a sphere, a cylinder and a torus-like one. These are stabilized by virtue of the background fluxes of M5-branes. The torus-like M2-brane configuration has winding and momentum numbers of 11th direction, and in terms of the type IIA superstring theory, this corresponds to a torus-like D2-brane with electric and magnetic fluxes on it. We also reproduce the same configuration from a non-abelian Born-Infeld action for D0-branes. It will be a construction of closed strings from D0-branes. An electric flux quantization condition on the D2-brane is also discussed in terms of D0-branes.Comment: 33 pages, 6 figures, references and footnote added, confusing expressions and introduction are improved, version to appear in JHE

Pure type I supergravity and DE(10)

We establish a dynamical equivalence between the bosonic part of pure type I supergravity in D=10 and a D=1 non-linear sigma-model on the Kac-Moody coset space DE(10)/K(DE(10)) if both theories are suitably truncated. To this end we make use of a decomposition of DE(10) under its regular SO(9,9) subgroup. Our analysis also deals partly with the fermionic fields of the supergravity theory and we define corresponding representations of the generalized spatial Lorentz group K(DE(10)).Comment: 28 page

Supermembranes and Super Matrix Models

We review recent developments in the theory of supermembranes and their relation to matrix models.Comment: Invited lecture presented at the Corfu Workshop, September 20 - 26, 1998, of the TMR Project "Quantum Aspects of Gauge Theories, Supersymmetry and Unification" (ERBFMRXCT96-0045), to appear in the proceedings. Latex 41 p