Results for "Michael M. Hull"

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Small cancellation in acylindrically hyperbolic groupsAug 20 2013May 21 2015We generalize a version of small cancellation theory to the class of acylindrically hyperbolic groups. This class contains many groups which admit some natural action on a hyperbolic space, including non-elementary hyperbolic and relatively hyperbolic ... More
Conjugacy Growth in Polycyclic GroupsJun 05 2010In this paper, we consider the conjugacy growth function of a group, which counts the number of conjugacy classes which intersect a ball of radius $n$ centered at the identity. We prove that in the case of virtually polycyclic groups, this function is ... More
How students blend conceptual and formal mathematical reasoning in solving physics problemsFeb 16 2011Dec 05 2013Current conceptions of expert problem solving depict physical/conceptual reasoning and formal mathematical reasoning as separate steps: a good problem solver first translates a physical Current conceptions of quantitative problem-solving expertise in ... More
Mathematical Sensemaking as Seeking Coherence between Calculations and Concepts: Instruction and Assessments for Introductory PhysicsMar 13 2019Mar 18 2019What kind of problem-solving instruction can help students apply what they have learned to solve the new and unfamiliar problems they will encounter in the future? We propose that mathematical sensemaking, the practice of seeking coherence between formal ... More
Mathematical Sensemaking as Seeking Coherence between Calculations and Concepts: Instruction and Assessments for Introductory PhysicsMar 13 2019What kind of problem-solving instruction can help students apply what they have learned to solve the new and unfamiliar problems they will encounter in the future? We propose that mathematical sensemaking, the practice of seeking coherence between formal ... More
D-brane Wess--Zumino actions, T-duality and the cosmological constantApr 19 1996Jun 06 1996A geometrical formulation of the T-duality rules for type II superstring Ramond--Ramond fields is presented. This is used to derive the Wess-Zumino terms in superstring D-brane actions, including terms proportional to the mass parameter of the IIA theory, ... More
Abelian splittings of Right-Angled Artin GroupsJan 31 2015We characterize when (and how) a Right-Angled Artin group splits nontrivially over an abelian subgroup.
Duality and Strings, Space and TimeNov 11 1999Duality symmetries in M--theory and string theory are reviewed, with particular emphasis on the way in which string winding modes and brane wrapping modes can lead to new spatial dimensions. Brane world-volumes wrapping around Lorentzian tori can give ... More
Massive String Theories From M-Theory and F-TheoryNov 02 1998Dec 15 1998The massive IIA string theory whose low energy limit is the massive supergravity theory constructed by Romans is obtained from M-theory compactified on a 2-torus bundle over a circle in a limit in which the volume of the bundle shrinks to zero. The massive ... More
Non-Abelian Gravity and Antisymmetric Tensor Gauge TheoryAug 08 1997Sep 19 1997A non-abelian generalisation of a theory of gravity coupled to a 2-form gauge field and a dilaton is found, in which the metric and 3-form field strength are Lie algebra-valued. In the abelian limit, the curvature with torsion is self-dual in four dimensions, ... More
The Geometric Structure of $W_N$-GravityMar 11 1993The full non-linear structure of the action and transformation rules for $\W_N$-gravity coupled to matter are obtained from a non-linear truncation of those for $w_ \infty$ gravity. The geometry of the construction is discussed, and it is shown that the ... More
Geometry and W-GravityJan 15 1993The higher-spin geometries of $W_\infty$-gravity and $W_N$-gravity are analysed and used to derive the complete non-linear structure of the coupling to matter and its symmetries. The symmetry group is a subgroup of the symplectic diffeomorphisms of the ... More
Finite Gauge Transformations and Geometry in Double Field TheoryJun 30 2014Recently proposed forms for gauge transformations with finite parameters in double field theory are discussed and problematic issues are identified. A new form for finite gauge transformations is derived that reveals the underlying gerbe structure and ... More
Domain Wall and de Sitter Solutions of Gauged SupergravityOct 04 2001Oct 23 2001BPS domain wall solutions of gauged supergravities are found, including those theories which have non-compact gauge groups. These include models that have both an unstable de Sitter solution and stable domain wall solutions.
Duality in Gravity and Higher Spin Gauge FieldsJul 18 2001Sep 03 2001Dual field theory realisations are given for linearised gravity in terms of gauge fields in exotic representations of the Lorentz group. The field equations and dual representations are discussed for a wide class of higher spin gauge fields. For non-linear ... More
String Dynamics at Strong CouplingDec 21 1995Mar 08 1996The dynamics of superstring, supergravity and M theories and their compactifications are probed by studying the various perturbation theories that emerge in the strong and weak coupling limits for various directions in coupling constant space. The results ... More
Classical and Quantum W-GravityJan 28 1992Jan 30 1992Classical W-gravities and the corresponding quantum theories are reviewed. W-gravities are higher-spin gauge theories in two dimensions whose gauge algebras are W-algebras. The geometrical structure of classical W-gravity is investigated, leading to surprising ... More
Doubled Geometry and T-FoldsMay 15 2006Jul 02 2007The doubled formulation of string theory, which is T-duality covariant and enlarges spacetime with extra coordinates conjugate to winding number, is reformulated and its geometric and topological features examined. It is used to formulate string theory ... More
A Geometry for Non-Geometric String BackgroundsJun 11 2004Jul 14 2005A geometric string solution has background fields in overlapping coordinate patches related by diffeomorphisms and gauge transformations, while for a non-geometric background this is generalised to allow transition functions involving duality transformations. ... More
Symmetries and Compactifications of (4,0) Conformal GravityNov 23 2000The free (4,0) superconformal theory in 6 dimensions and its toroidal dimensional reductions are studied. The reduction to four dimensions on a 2-torus has an $SL(2,\Z)$ duality symmetry that acts non-trivially on the linearised gravity sector, interchanging ... More
Timelike T-Duality, de Sitter Space, Large $N$ Gauge Theories and Topological Field TheoryJun 17 1998Aug 11 1998T-Duality on a timelike circle does not interchange IIA and IIB string theories, but takes the IIA theory to a type $IIB^*$ theory and the IIB theory to a type $IIA^*$ theory. The type $II^*$ theories admit E-branes, which are the images of the type II ... More
Gauged Heterotic Sigma-ModelsOct 20 1993Oct 22 1993The gauging of isometries in general sigma-models which include fermionic terms which represent the interaction of strings with background Yang-Mills fields is considered. Gauging is possible only if certain obstructions are absent. The quantum gauge ... More
W-GravityNov 24 1992The geometric structure of theories with gauge fields of spins two and higher should involve a higher spin generalisation of Riemannian geometry. Such geometries are discussed and the case of $W_\infty$-gravity is analysed in detail. While the gauge group ... More
Generalised Geometry for M-TheoryJan 22 2007Generalised geometry studies structures on a d-dimensional manifold with a metric and 2-form gauge field on which there is a natural action of the group SO(d,d). This is generalised to d-dimensional manifolds with a metric and 3-form gauge field on which ... More
String-String Duality in Ten DimensionsJun 29 1995The heterotic string occurs as a soliton of the type I superstring in ten dimensions, supporting the conjecture that these two theories are equivalent. The conjecture that the type IIB string is self-dual, with the strong coupling dynamics described by ... More
Conjugacy growth of finitely generated groupsJul 10 2011Jan 27 2015We show that every non-decreasing function $f\colon \mathbb N\to \mathbb N$ bounded from above by $a^n$ for some $a\ge 1$ can be realized (up to a natural equivalence) as the conjugacy growth function of a finitely generated group. We also construct a ... More
Gauged D=9 Supergravities and Scherk-Schwarz ReductionMar 15 2002Aug 05 2002Generalised Scherk-Schwarz reductions in which compactification on a circle is accompanied by a twist with an element of a global symmetry G typically lead to gauged supergravities and are classified by the monodromy matrices, up to conjugation by the ... More
Conformal Non-Geometric Gravity in Six Dimensions and M-Theory above the Planck EnergyNov 19 2000Nov 23 2000The proposal that a strong coupling limit of the five-dimensional type II string theory (M-theory compactified on a 6-torus) in which the Planck length becomes infinite could give a six-dimensional superconformal phase of M-theory is reviewed. This limit ... More
Duality and the Signature of Space-TimeJul 17 1998Nov 19 1998Versions of M-theory are found in spacetime signatures (9,2) and (6,5), in addition to the usual M-theory in 10+1 dimensions, and these give rise to type IIA string theories in 10-dimensional spacetime signatures (10,0),(9,1),(8,2),(6,4) and (5,5), and ... More
U-Duality and BPS Spectrum of Super Yang-Mills Theory and M-TheoryDec 07 1997It is shown that the BPS spectrum of Super-Yang-Mills theory on $T^d\times \R$, which fits into representations of the U-duality group for M-theory compactified on $T^{d}$, in accordance with the matrix-theory conjecture, in fact fits into representations ... More
Actions For (2,1) Sigma-Models and StringsFeb 07 1997Effective actions are derived for (2,0) and (2,1) superstrings by studying the corresponding sigma-models. The geometry is a generalisation of Kahler geometry involving torsion and the field equations imply that the curvature with torsion is self-dual ... More
De Sitter Space in Supergravity and M TheorySep 27 2001Oct 23 2001Two ways in which de Sitter space can arise in supergravity theories are discussed. In the first, it arises as a solution of a conventional supergravity, in which case it necessarily has no Killing spinors. For example, de Sitter space can arise as a ... More
Gravitational Duality, Branes and ChargesMay 21 1997Jun 23 1997It is argued that D=10 type II strings and M-theory in D=11 have D-5 branes and 9-branes that are not standard p-branes coupled to anti-symmetric tensors. The global charges in a D-dimensional theory of gravity consist of a momentum $P_M$ and a dual D-5 ... More
Transitivity degrees of countable groups and acylindrical hyperbolicityJan 17 2015We prove that every countable acylindrically hyperbolic group admits a highly transitive action with finite kernel. This theorem uniformly generalizes many previously known results and allows us to answer a question of Garion and Glassner on the existence ... More
Induced quasi-cocycles on groups with hyperbolically embedded subgroupsMar 24 2012Mar 05 2013Let G be a group, H a hyperbolically embedded subgroup of G, V a normed G-module, U an H-invariant submodule of V. We propose a general construction which allows to extend 1-quasi-cocycles on H with values in U to 1-quasi-cocycles on G with values in ... More
Conjugacy growth of finitely generated groupsJul 10 2011Jan 30 2017We show that every non-decreasing function $f\colon \mathbb N\to \mathbb N$ bounded from above by $a^n$ for some $a\ge 1$ can be realized (up to a natural equivalence) as the conjugacy growth function of a finitely generated group. We also construct a ... More
D-branes and the Noncommutative TorusNov 21 1997Nov 28 1997We show that in certain superstring compactifications, gauge theories on noncommutative tori will naturally appear as D-brane world-volume theories. This gives strong evidence that they are well-defined quantum theories. It also gives a physical derivation ... More
Global Aspects of T-Duality, Gauged Sigma Models and T-FoldsApr 25 2006Sep 28 2007The gauged sigma-model argument that string backgrounds related by T-dual give equivalent quantum theories is revisited, taking careful account of global considerations. The topological obstructions to gauging sigma-models give rise to obstructions to ... More
BPS Supermultiplets in Five DimensionsApr 11 2000Jul 05 2000BPS representations of 5-dimensional supersymmetry algebras are classified. For BPS states preserving 1/2 the supersymmetry, there are two distinct classes of multiplets for N=4 supersymmetry and three classes for N=8 supersymmetry. For N=4 matter theories, ... More
Strongly Coupled Gravity and DualityApr 27 2000Jun 29 2000A strong coupling limit of theories whose low-energy effective field theory is 5-dimensional N=8 supergravity is proposed in which the gravitational coupling becomes large. It is argued that, if this limit exists, it should be a 6-dimensional theory with ... More
The Non-Perturbative SO(32) Heterotic StringDec 22 1998The SO(32) heterotic string can be obtained from the type IIB string by gauging a discrete symmetry that acts as $(-1)^{F_L}$ on the perturbative string states and reverses the parity of the D-string. Consistency requires the presence of 32 NS 9-branes ... More
Decoupling Limits in M-TheoryMar 15 1998Apr 22 1998Limits of a system of N Dn-branes in which the bulk and string degrees of freedom decouple to leave a `matter' theory are investigated and, for n>4, either give a free theory or require taking $N \to \infty$. The decoupled matter theory is described at ... More
The Geometry of Supersymmetric Quantum MechanicsOct 04 1999One-dimensional sigma-models with N supersymmetries are considered. For conventional supersymmetries there must be N-1 complex structures satisfying a Clifford algebra and the constraints on the target space geometry can be formulated in terms of these. ... More
Matrix Theory, U-Duality and Toroidal Compactifications of M-TheoryNov 24 1997Oct 07 1998Using U-duality, the properties of the matrix theories corresponding to the compactification of M-theory on $T^d$ are investigated. The couplings of the $d+1$ dimensional effective Super-Yang-Mills theory to all the M-theory moduli is deduced and the ... More
Lectures on W-Gravity, W-Geometry and \W-StringsFeb 23 1993Lectures given at the Trieste Summer School, 1992. These notes are an update of my review article "Classical and Quantum W-Gravity", preprint QMW-92-1, published in in "Strings and Symmetries 1991", with some extra material on W-geometry, W-symmetry in ... More
New Gauged N=8, D=4 SupergravitiesApr 18 2002Apr 25 2002New gaugings of four dimensional N=8 supergravity are constructed, including one which has a Minkowski space vacuum that preserves N=2 supersymmetry and in which the gauge group is broken to $SU(3)xU(1)^2$. Previous gaugings used the form of the ungauged ... More
Higher Dimensional Yang-Mills Theories and Topological TermsOct 21 1997Nov 04 1997Higher dimensional generalisations of self-duality conditions and of theta angle terms are analysed in Yang-Mills theories. For the theory on a torus, the torus metric and various antisymmetric tensors are viewed as coupling constants related by U-duality, ... More
The Geometry of $N=2$ Strings with TorsionJun 28 1996Aug 28 1996$N=2$ string theories are formulated in space-times with 2 space and 2 time dimensions. If the world-sheet matter system consists of 2 chiral superfields, the space-time is Kahler and the dynamics are those of anti-self-dual gravity. If instead one chiral ... More
New Realisations of Minimal Models and the Structure of W-StringsMay 21 1993The quantization of a free boson whose momentum satisfies a cubic constraint leads to a $c=\ha$ conformal field theory with a BRST symmetry. The theory also has a $W_\infty $ symmetry in which all the generators except the stress-tensor are BRST-exact ... More
Singular Contractions of W-algebrasJun 08 1992Many $W$-algebras (e.g. the $W_N$ algebras) are consistent for all values of the central charge except for a discrete set of exceptional values. We show that such algebras can be contracted to new consistent degenerate algebras at these exceptional values ... More
Wrapped Branes and SupersymmetrySep 03 1997Nov 24 1997Configurations of two or more branes wrapping different homology cycles of space-time are considered and the amount of supersymmetry preserved is analysed, generalising the analysis of multiple branes in flat space. For K3 compactifications, these give ... More
Duality and Moduli Spaces for Time-Like ReductionsMar 28 1998We consider the dimensional reduction/compactification of supergravity, string and M-theories on tori with one time-like circle. We find the coset spaces in which the massless scalars take their values, and identify the discrete duality groups.
Finite Gauge Transformations and Geometry in Extended Field TheoryDec 11 2015The recently derived expressions for finite gauge transformations in double field theory with duality group O(d,d) are generalised to give expressions for finite gauge transformations for extended field theories with duality group SL(5,R), SO(5,5) and ... More
Rigid foldability of the augmented square twistSep 13 2018Define the augmented square twist origami crease pattern to be the classic square twist crease pattern with one crease added along a diagonal of the twisted square. In this paper we fully describe the rigid foldability of this new crease pattern. Specifically, ... More
On $W_{\infty/2}$ StringsApr 13 1994The string theory defined by gauging $\W_{\infty/2}$, the sub-algebra of $\W_{\infty}$ generated by the currents of even spin, is discussed. The critical value of the central charge is calculated using zeta-function techniques and shown to be $c=1$. A ... More
Emergent Time and the M5-BraneMar 18 2014We consider the maximal super-Yang-Mills theory in 5 Euclidean dimensions with SO(5) R-symmetry and 16 supersymmetries. We argue that the strong coupling limit of this theory (with a possible UV completion) has an emergent time dimension and gives a description ... More
Black Holes and U-DualityJun 28 1996Nov 04 1996We find the general charged rotating black hole solutions of the maximal supergravities in dimensions $4\le D\le 9$ arising from toroidally compactified Type II string or M-theories. In each dimension, these are obtained by acting on a generating solution ... More
Higher-Spin Gauge Fields and DualityJan 28 2005Feb 24 2005We review the construction of free gauge theories for gauge fields in arbitrary representations of the Lorentz group in $D$ dimensions. We describe the multi-form calculus which gives the natural geometric framework for these theories. We also discuss ... More
A Cartan-Hadamard type result for relatively hyperbolic groupsNov 04 2013In this article, we prove that if a finitely presented group has an asymptotic cone which is tree-graded with respect to a precise set of pieces then it is relatively hyperbolic. This answers a question of M. Sapir.
Intrinsic Geometry of D-BranesApr 02 1997May 20 1997We obtain forms of Born-Infeld and D-brane actions that are quadratic in derivatives of $X$ and linear in $F_{\mu \nu}$ by introducing an auxiliary `metric' which has both symmetric and anti-symmetric parts, generalising the simplification of the Nambu-Goto ... More
A Chiral Perturbation Expansion for GravityNov 18 2005Dec 12 2005A formulation of Einstein gravity, analogous to that for gauge theory arising from the Chalmers-Siegel action, leads to a perturbation theory about an asymmetric weak coupling limit that treats positive and negative helicities differently. We find power ... More
Geometric Actions for D-Branes and M-BranesFeb 25 1998Apr 06 1998New forms of Born-Infeld, D-brane and M theory five-brane actions are found which are quadratic in the abelian field strength. The gauge fields couple both to a background or induced metric and a new auxiliary metric, whose elimination reproduces the ... More
pp-waves in 11-dimensions with extra supersymmetryMar 27 2002Apr 10 2002The Killing spinor equations for pp-wave solutions of eleven dimensional supergravity are analysed and it is shown that there are solutions that preserve 18,20,22 and 24 supersymmetries, in addition to the generic solution preserving 16 supersymmetries ... More
De Sitter Space from Warped Supergravity SolutionsNov 08 2001The solutions of 10 and 11 dimensional supergravity that are warped products of de Sitter space with a non-compact `internal' space are investigated. A convenient form of the metric is found and it is shown that in each case the internal space is asymptotic ... More
BPS States with Extra SupersymmetrySep 14 1999Nov 23 1999A state saturating a BPS bound derived from a supersymmetry algebra preserves some fraction of the supersymmetry. This fraction of supersymmetry depends on the charges carried by the system, and we show that in general there are configurations of charges ... More
Branes, Times and DualitiesAug 12 1998Dualities link M-theory, the 10+1 dimensional strong coupling limit of the IIA string, to other 11-dimensional theories in signatures 9+2 and 6+5, and to type II string theories in all 10-dimensional signatures. We study the Freund-Rubin-type compactifications ... More
Duality in the Type--II Superstring Effective ActionApr 16 1995Apr 18 1996We derive the T-duality transformations that transform a general d=10 solution of the type-IIA string with one isometry to a solution of the type-IIB string with one isometry and vice versa. In contrast to other superstring theories, the T-duality transformations ... More
Pseudo-DualityMar 03 1995Proper symmetries act on fields while pseudo-symmetries act on both fields and coupling constants. We identify the pseudo-duality groups that act as symmetries of the equations of motion of general systems of scalar and vector fields and apply our results ... More
Flux Compactifications of String Theory on Twisted ToriMar 14 2005Global aspects of Scherk-Schwarz dimensional reduction are discussed and it is shown that it can usually be viewed as arising from a compactification on the compact space obtained by identifying a (possibly non-compact) group manifold G under a discrete ... More
Conformal Points and Duality of Non-Abelian Thirring Models and Interacting WZNW ModelsMar 03 1995Nov 09 1995We show that the strong coupling phase of the non-Abelian Thirring model is dual to the weak-coupling phase of a system of two WZNW models coupled to each other through a current-current interaction. This latter system is integrable and is related to ... More
The Gauged (2,1) Heterotic Sigma-ModelAug 08 1997Dec 22 1997The geometry of (2,1) supersymmetric sigma-models with isometry symmetries is discussed. The gauging of such symmetries in superspace is then studied. We find that the coupling to the (2,1) Yang-Mills supermultiplet can be achieved provided certain geometric ... More
Conformal Invariance and Duality in Self-Dual Gravity and (2,1) Heterotic String TheoryOct 10 1997Dec 22 1997A system of gravity coupled to a 2-form gauge field, a dilaton and Yang-Mills fields in $2n$ dimensions arises from the (2,1) sigma model or string. The field equations imply that the curvature with torsion and Yang-Mills field strength are self-dual ... More
Geometry, Isometries and Gauging of (2,1) Heterotic Sigma-ModelsDec 19 1996Mar 12 1997The geometry of (2,1) supersymmetric sigma-models is reviewed and the conditions under which they have isometry symmetries are analysed. Certain potentials are constructed that play an important role in the gauging of such symmetries. The gauged action ... More
Particles, Superparticles and Super Yang--MillsAug 05 1992This paper is concerned with theories describing spinning particles that are formulated in terms of actions possessing either local world-line supersymmetry or local fermionic {\it kappa} invariance. These classical actions are obtained by adding a finite ... More
Non-geometric backgrounds, doubled geometry and generalised T-dualityFeb 23 2009String backgrounds with a local torus fibration such as T-folds are naturally formulated in a doubled formalism in which the torus fibres are doubled to include dual coordinates conjugate to winding number. Here we formulate and explore a generalisation ... More
Gauge Symmetry, T-Duality and Doubled GeometryNov 29 2007String compactifications with T-duality twists are revisited and the gauge algebra of the dimensionally reduced theories calculated. These reductions can be viewed as string theory on T-fold backgrounds, and can be formulated in a `doubled space' in which ... More
Breaking the Radio - Gamma-Ray Connection in Arp 220Jan 14 2019Recent analyses of the gamma-ray spectrum from the ultra-luminous infrared galaxy Arp 220 have revealed a discrepancy in the cosmic ray energy injection rates derived from the gamma-rays versus the radio emission. While the observed radio emission is ... More
Enhanced Gauge Symmetries in Superstring TheoriesMay 12 1995Mar 08 1996Certain four-dimensional $N=4$ supersymmetric theories have special vacua in which massive charged vector supermultiplets become massless, resulting in an enhanced non-abelian gauge symmetry. We show here that any two $N=4$ theories having the same Bogomolnyi ... More
Unity of Superstring DualitiesOct 21 1994Jan 13 1995The effective action for type II string theory compactified on a six torus is $N=8$ supergravity, which is known to have an $E_{7}$ duality symmetry. We show that this is broken by quantum effects to a discrete subgroup, $E_7(\Z)$, which contains both ... More
The Geometry of Sigma-Models with Twisted SupersymmetryJul 07 1999We investigate the relation between supersymmetry and geometry for two dimensional sigma models with target spaces of arbitrary signature, and Lorentzian or Euclidean world-sheets. In particular, we consider twisted forms of the two-dimensional $(p,q)$ ... More
Flux Compactifications of M-Theory on Twisted ToriMar 12 2006We find the bosonic sector of the gauged supergravities that are obtained from 11-dimensional supergravity by Scherk-Schwarz dimensional reduction with flux to any dimension D. We show that, if certain obstructions are absent, the Scherk-Schwarz ansatz ... More
Worldvolume Theories, Holography, Duality and TimeNov 11 1999Duality transformations involving compactifications on timelike as well as spacelike circles link M-theory, the 10+1-dimensional strong coupling limit of IIA string theory, to other 11-dimensional theories in signatures 9+2 and 6+5 and to type II string ... More
An extremely high velocity molecular jet surrounded by an ionized cavity in the protostellar source Serpens SMM1Apr 12 2016May 22 2016We report ALMA observations of a one-sided, high-velocity ($\sim$80 km s$^{-1}$) CO($J = 2 \rightarrow 1$) jet powered by the intermediate-mass protostellar source Serpens SMM1-a. The highly collimated molecular jet is flanked at the base by a wide-angle ... More
T-Duality in $(2,1)$ SuperspaceJan 03 2019Jan 18 2019We find the T-duality transformation rules for 2-dimensional (2,1) supersymmetric sigma-models in (2,1) superspace. Our results clarify certain aspects of the (2,1) sigma model geometry relevant to the discussion of T-duality. The complexified duality ... More
T-duality, Gerbes and Loop SpacesOct 26 2007We revisit sigma models on target spaces given by a principal torus fibration $X\to M$, and show how treating the 2-form B as a gerbe connection captures the gauging obstructions and the global constraints on the T-duality. We show that a gerbe connection ... More
Einstein Supergravity and New Twistor String TheoriesJun 29 2006Oct 24 2007A family of new twistor string theories is constructed and shown to be free from world-sheet anomalies. The spectra in space-time are calculated and shown to give Einstein supergravities with second order field equations instead of the higher derivative ... More
Protostellar Disk Formation Enabled by Weak, Misaligned Magnetic FieldsJan 23 2013The gas from which stars form is magnetized, and strong magnetic fields can efficiently transport angular momentum. Most theoretical models of this phenomenon find that it should prevent formation of large (>100 AU), rotationally-supported disks around ... More
Potentials for (p,0) and (1,1) supersymmetric sigma models with torsionJul 02 1993Using (1,0) superfield methods, we determine the general scalar potential consistent with off-shell (p,0) supersymmetry and (1,1) supersymmetry in two-dimensional non-linear sigma models with torsion. We also present an extended superfield formulation ... More
880 $μ$m SMA polarization observations of the quasar 3C 286Aug 22 2016Sep 30 2016For decades, the bright radio quasar 3C 286 has been widely recognized as one of the most reliable polarization calibrators at centimeter wavelengths because of its unchanging polarization position angle and high polarization percentage. However, it has ... More
Holonomy and Symmetry in M-theoryMay 05 2003May 07 2003Supersymmetric solutions of 11-dimensional supergravity can be classified according to the holonomy of the supercovariant derivative arising in the Killing spinor condition. It is shown that the holonomy must be contained in $\SL(32,\R)$. The holonomies ... More
ALMA observations of dust polarization and molecular line emission from the Class 0 protostellar source Serpens SMM1Jul 12 2017We present high angular resolution dust polarization and molecular line observations carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the Class 0 protostar Serpens SMM1. By complementing these observations with new polarization ... More
Performance of a simple proxy for U.S. cloud-to-ground lightningOct 01 2018The product of convective available potential energy (CAPE) and precipitation rate has previously been used as a proxy for cloud-to-ground (CG) lightning flash counts in climate change applications. Here the ability of this proxy, denoted CP, to represent ... More
Generalized Kahler geometry and gerbesNov 21 2008We introduce and study the notion of a biholomorphic gerbe with connection. The biholomorphic gerbe provides a natural geometrical framework for generalized Kahler geometry in a manner analogous to the way a holomorphic line bundle is related to Kahler ... More
Euclidean Supersymmetry, Twisting and Topological Sigma ModelsMay 21 2008We discuss two dimensional N-extended supersymmetry in Euclidean signature and its R-symmetry. For N=2, the R-symmetry is SO(2)\times SO(1,1), so that only an A-twist is possible. To formulate a B-twist, or to construct Euclidean N=2 models with H-flux ... More
All supersymmetric solutions of minimal supergravity in five dimensionsSep 13 2002Sep 02 2003All purely bosonic supersymmetric solutions of minimal supergravity in five dimensions are classified. The solutions preserve either one half or all of the supersymmetry. Explicit examples of new solutions are given, including a large family of plane-fronted ... More
Equipartition and Cosmic Ray Energy Densities in Central Molecular Zones of StarburstsDec 02 2015The energy densities in magnetic fields and cosmic rays (CRs) in galaxies are often assumed to be in equipartition, allowing for an indirect estimate of the magnetic field strength from the observed radio synchrotron spectrum. However, both primary and ... More
Lessons from Comparisons between the Nuclear Region of the Milky Way & Those in Nearby SpiralsDec 16 2013The Milky Way appears is a typical barred spiral, and comparisons can be made between its nuclear region and those of structurally similar nearby spirals. Maffei 2, M83, IC 342 and NGC 253 are nearby systems whose nuclear region properties contrast with ... More
Generalized Calabi-Yau metric and Generalized Monge-Ampere equationMay 31 2010In the neighborhood of a regular point, generalized Kahler geometry admits a description in terms of a single real function, the generalized Kahler potential. We study the local conditions for a generalized Kahler manifold to be a generalized Calabi-Yau ... More
BPS states of D=4 N=1 supersymmetryJan 06 2000Mar 03 2000We find the combinations of momentum and domain-wall charges corresponding to BPS states preserving 1/4, 1/2 or 3/4 of D=4 N=1 supersymmetry, and we show how the supersymmetry algebra implies their stability. These states form the boundary of the convex ... More
Cosmic Rays, Gamma-Rays, and Neutrinos in the Starburst Nuclei of Arp 220Jun 16 2015Jul 27 2015The cores of Arp 220, the closest ultra-luminous infrared starburst galaxy, provide an opportunity to study interactions of cosmic rays under extreme conditions. In this paper, we model the populations of cosmic rays produced by supernovae in the central ... More