Results for "J. Burt"

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Rationality does not specialize among terminal varietiesAug 05 2015A limit of rational varieties need not be rational, even if all varieties in the family are projective and have at most terminal singularities.
The Chow ring of a classifying spaceFeb 20 1998We define the Chow ring of the classifying space of a linear algebraic group. In all the examples where we can compute it, such as the symmetric groups and the orthogonal groups, it is isomorphic to a natural quotient of the complex cobordism ring of ... More
Hilbert's fourteenth problem over finite fields, and a conjecture on the cone of curvesAug 05 2008We give examples over arbitrary fields of rings of invariants that are not finitely generated. The group involved can be as small as three copies of the additive group, as in Mukai's examples over the complex numbers. The failure of finite generation ... More
The integral Hodge conjecture for 3-folds of Kodaira dimension zeroJul 19 2019We prove the integral Hodge conjecture for all 3-folds X of Kodaira dimension zero with H^0(X, K_X) not zero. This generalizes earlier results of Voisin and Grabowski. The assumption is sharp, in view of counterexamples by Benoist and Ottem. We also prove ... More
Algebraic surfaces and hyperbolic geometryAug 23 2010This is a survey of the Kawamata-Morrison cone conjecture on the structure of Calabi-Yau varieties and more generally Calabi-Yau pairs. We discuss the proof of the cone conjecture for algebraic surfaces, with plenty of examples. We show that the automorphism ... More
Complex varieties with infinite Chow groups modulo 2Feb 06 2015We show that for a very general principally polarized complex abelian 3-fold, the Chow group of algebraic cycles is infinite modulo every prime number. In particular, this gives the first examples of complex varieties with infinite Chow groups modulo ... More
Adjoint functors on the derived category of motivesFeb 17 2015Voevodsky's derived category of motives is the main arena today for the study of algebraic cycles and motivic cohomology. In this paper we study whether the inclusions of three important subcategories of motives have a left or right adjoint. These adjoint ... More
The motive of a classifying spaceJul 05 2014Nov 28 2014We give the first examples of finite groups G such that the Chow ring of the classifying space BG depends on the base field, even for fields containing the algebraic closure of Q. As a tool, we give several characterizations of the varieties which satisfy ... More
The cone conjecture for Calabi-Yau pairs in dimension twoJan 21 2009Feb 14 2009We prove the Morrison-Kawamata cone conjecture for klt Calabi-Yau pairs in dimension 2. That is, for a large class of rational surfaces as well as K3 surfaces and abelian surfaces, the action of the automorphism group of the surface on the convex cone ... More
The curvature of a Hessian metricJan 27 2004Feb 13 2004Following P. M. H. Wilson's paper on sectional curvatures of Kahler moduli, we consider a natural Riemannian metric on a hypersurface f=1 in a real vector space, defined using the Hessian of a homogeneous polynomial f. We give examples to answer a question ... More
Crescent configurationsSep 24 2015In 1989, Erd\H{o}s conjectured that for a sufficiently large $n$ it is impossible to place $n$ points in general position in a plane such that for every $1\le i \le n-1$ there is a distance that occurs exactly $i$ times. For small $n$ this is possible ... More
Perturbative Anti-Brane Potentials in Heterotic M-theoryJan 03 2007We derive the perturbative four-dimensional effective theory describing heterotic M-theory with branes and anti-branes in the bulk space. The back-reaction of both the branes and anti-branes is explicitly included. To first order in the heterotic strong-coupling ... More
Non-vanishing Superpotentials in Heterotic String Theory and Discrete TorsionNov 07 2016We study the non-perturbative superpotential in E_8 x E_8 heterotic string theory on a non-simply connected Calabi-Yau manifold X, as well as on its simply connected covering space \tilde{X}. The superpotential is induced by the string wrapping holomorphic, ... More
Optimizing Pulsar Timing Arrays to Maximize Gravitational Wave Single Source Detection: a First CutMay 27 2010Jan 24 2011Pulsar Timing Arrays (PTAs) use high accuracy timing of a collection of low timing noise pulsars to search for gravitational waves in the microhertz to nanohertz frequency band. The sensitivity of such a PTA depends on (a) the direction of the gravitational ... More
The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big BangMar 29 2001Aug 15 2001We propose a cosmological scenario in which the hot big bang universe is produced by the collision of a brane in the bulk space with a bounding orbifold plane, beginning from an otherwise cold, vacuous, static universe. The model addresses the cosmological ... More
Higher-Derivative Gravity in String TheoryMay 21 1996We explicitly extract the structure of higher-derivative curvature-squared terms at genus 0 and 1 in the d=4 heterotic string effective action compactified on symmetric orbifolds by computing on-shell S-matrix superstring amplitudes. In particular, this ... More
Density Perturbations in the Ekpyrotic ScenarioSep 06 2001Mar 06 2002We study the generation of density perturbations in the ekpyrotic scenario for the early universe, including gravitational backreaction. We expose interesting subtleties that apply to both inflationary and ekpyrotic models. Our analysis includes a detailed ... More
Benford's Law and Continuous Dependent Random VariablesSep 22 2013Mar 09 2018Many mathematical, man-made and natural systems exhibit a leading-digit bias, where a first digit (base 10) of 1 occurs not 11\% of the time, as one would expect if all digits were equally likely, but rather 30\%. This phenomenon is known as Benford's ... More
A Cosmological Mechanism for Stabilizing ModuliJan 19 2000Feb 05 2000In this paper, we show how the generic coupling of moduli to the kinetic energy of ordinary matter fields results in a cosmological mechanism that influences the evolution and stability of moduli. As an example, we reconsider the problem of stabilizing ... More
A Brief Comment on "The Pyrotechnic Universe"May 22 2001We respond to the criticisms by Kallosh, Kofman and Linde concerning our proposal of the ekpyrotic universe scenario. We point out a number of errors in their considerations and argue that, at this stage, the ekpyrotic model is a possible alternative ... More
How to Fool Radiologists with Generative Adversarial Networks? A Visual Turing Test for Lung Cancer DiagnosisOct 26 2017Jan 09 2018Discriminating lung nodules as malignant or benign is still an underlying challenge. To address this challenge, radiologists need computer aided diagnosis (CAD) systems which can assist in learning discriminative imaging features corresponding to malignant ... More
Pseudo-abelian varietiesApr 05 2011Feb 27 2013Chevalley's theorem states that every smooth connected algebraic group over a perfect field is an extension of an abelian variety by a smooth connected affine group. That fails when the base field is not perfect. We define a pseudo-abelian variety over ... More
The Atiyah Class and Complex Structure Stabilization in Heterotic Calabi-Yau CompactificationsJul 25 2011Holomorphic gauge fields in N=1 supersymmetric heterotic compactifications can constrain the complex structure moduli of a Calabi-Yau manifold. In this paper, the tools necessary to use holomorphic bundles as a mechanism for moduli stabilization are systematically ... More
Moving codimension-one subvarieties over finite fieldsDec 12 2007We give the first examples of nef line bundles on smooth projective varieties over finite fields which are not semi-ample. More concretely, we find smooth curves on smooth projective surfaces over finite fields such that the normal bundle has degree zero, ... More
Jumping of the nef cone for Fano varietiesJul 21 2009Jan 08 2010We construct Q-factorial terminal Fano varieties, starting in dimension 4, whose nef cone jumps when the variety is deformed. It follows that de Fernex and Hacon's results on deformations of 3-dimensional Fanos are optimal. The examples are based on the ... More
The automorphism group of an affine quadricAug 03 2006We determine the automorphism group for a large class of affine quadric hypersurfaces over a field, viewed as affine algebraic varieties. In particular, we find that the group of real polynomial automorphisms of the n-sphere is just the orthogonal group ... More
Systematic Study of Au-Au Collisions with AGS Experiment E917Mar 30 2001The systematics of baryon stopping and strange particle production have been studied in Au+Au collisions at 6, 8, and 10.8 GeV per nucleon with AGS experiment E917. In particular, the systematic behavior of the proton yields, phi meson production, and ... More
Perturbative Reheating in Sneutrino-Higgs CosmologyApr 20 2018Sep 26 2018The theory of perturbative reheating in the Sneutrino-Higgs cosmology of the $B-L$ MSSM is presented. It is shown that following an epoch of inflation consistent with all Planck2015 data, the inflaton begins to oscillate around its minimum at zero and ... More
Curvature, diameter, and quotient manifoldsSep 13 2002Gromov showed that there is an upper bound on the Betti numbers of all closed Riemannian n-manifolds of nonnegative sectional curvature. Grove asked whether such manifolds (if simply connected) fall into only finitely many rational homotopy types. We ... More
Hodge theory of classifying stacksMar 10 2017Apr 15 2017We compute the Hodge and de Rham cohomology of the classifying space BG (defined as etale cohomology on the algebraic stack BG) for reductive groups G over many fields, including fields of small characteristic. These calculations have a direct relation ... More
Hodge structures of type (n,0,...,0,n)Feb 15 2014This paper determines all the possible endomorphism algebras for polarizable Q-Hodge structures of type (n,0,...,0,n). This generalizes the classification of the possible endomorphism algebras of abelian varieties by Albert and Shimura. As with abelian ... More
The failure of Kodaira vanishing for Fano varieties, and terminal singularities that are not Cohen-MacaulayOct 12 2017We show that the Kodaira vanishing theorem can fail on smooth Fano varieties of any characteristic p > 0. Taking cones over some of these varieties, we give the first examples of terminal singularities which are not Cohen-Macaulay. By a different method, ... More
Bott vanishing for algebraic surfacesDec 26 2018Bott proved a strong vanishing theorem for sheaf cohomology on projective space. It holds for toric varieties, but not for most other varieties. We prove Bott vanishing for the quintic del Pezzo surface, also known as the moduli space M_{0,5}^bar of 5-pointed ... More
Birational geometry of quadrics in characteristic 2Aug 03 2006A conic bundle or quadric bundle in characteristic 2 can have generic fiber which is nowhere smooth over the function field of the base variety. In that case, the generic fiber is called a quasilinear quadric. We solve some of the main problems of birational ... More
Line bundles with partially vanishing cohomologyJul 22 2010Define a line bundle L on a projective variety to be q-ample, for a natural number q, if tensoring with high powers of L kills coherent sheaf cohomology above dimension q. Thus 0-ampleness is the usual notion of ampleness. Intuitively, a line bundle is ... More
Yukawa Couplings in Heterotic Standard ModelsJan 27 2006In this paper, we present a formalism for computing the Yukawa couplings in heterotic standard models. This is accomplished by calculating the relevant triple products of cohomology groups, leading to terms proportional to Q*H*u, Q*Hbar*d, L*H*nu and ... More
Moduli Dependent Spectra of Heterotic CompactificationsMar 31 2004Apr 18 2004Explicit methods are presented for computing the cohomology of stable, holomorphic vector bundles on elliptically fibered Calabi-Yau threefolds. The complete particle spectrum of the low-energy, four-dimensional theory is specified by the dimensions of ... More
Bott vanishing for algebraic surfacesDec 26 2018Jun 07 2019Bott proved a strong vanishing theorem for sheaf cohomology on projective space. It holds for toric varieties, but not for most other varieties. We prove Bott vanishing for the quintic del Pezzo surface, also known as the moduli space M_{0,5}^bar of 5-pointed ... More
Essential dimension of the spin groups in characteristic 2Jan 21 2017Jan 28 2017We determine the essential dimension of the spin group Spin(n) as an algebraic group over a field of characteristic 2, for n at least 15. In this range, the essential dimension is the same as in characteristic not 2. In particular, it is exponential in ... More
The resolution property for schemes and stacksJul 23 2002We prove the equivalence of two fundamental properties of algebraic stacks: being a quotient stack in a strong sense, and the resolution property, which says that every coherent sheaf is a quotient of some vector bundle. Moreover, we prove these properties ... More
The integral cohomology of the Hilbert scheme of two pointsJun 02 2015The Hilbert scheme X^{[a]} of points on a complex manifold X is a compactification of the configuration space of a-element subsets of X. The integral cohomology of X^{[a]} is more subtle than the rational cohomology. In this paper, we compute the mod ... More
Cheeger manifolds and the classification of biquotientsOct 16 2002A closed manifold is called a biquotient if it is diffeomorphic to K\G/H for some compact Lie group G with closed subgroups K and H such that K acts freely on G/H. Biquotients are a major source of examples of Riemannian manifolds with nonnegative sectional ... More
A Heterotic Standard ModelJan 10 2005Apr 25 2005Within the context of the E_8 x E_8 heterotic superstring compactified on a smooth Calabi-Yau threefold with an SU(4) gauge instanton, we show the existence of simple, realistic N=1 supersymmetric vacua that are compatible with low energy particle physics. ... More
Stability of the Minimal Heterotic Standard Model BundleFeb 07 2006The observable sector of the "minimal heterotic standard model" has precisely the matter spectrum of the MSSM: three families of quarks and leptons, each with a right-handed neutrino, and one Higgs-Higgs conjugate pair. In this paper, it is explicitly ... More
Vector Bundle Extensions, Sheaf Cohomology, and the Heterotic Standard ModelMay 04 2005Jul 18 2005Stable, holomorphic vector bundles are constructed on an torus fibered, non-simply connected Calabi-Yau threefold using the method of bundle extensions. Since the manifold is multiply connected, we work with equivariant bundles on the elliptically fibered ... More
Higgs Doublets, Split Multiplets and Heterotic SU(3)_C x SU(2)_L x U(1)_Y SpectraSep 28 2004Nov 19 2004A methodology for computing the massless spectrum of heterotic vacua with Wilson lines is presented. This is applied to a specific class of vacua with holomorphic SU(5)-bundles over torus-fibered Calabi-Yau threefolds with fundamental group Z_2. These ... More
The Particle Spectrum of Heterotic CompactificationsMay 03 2004Techniques are presented for computing the cohomology of stable, holomorphic vector bundles over elliptically fibered Calabi-Yau threefolds. These cohomology groups explicitly determine the spectrum of the low energy, four-dimensional theory. Generic ... More
Torsion algebraic cycles and complex cobordismSep 23 1996Sep 24 1996We show that the cycle map on a variety X, from algebraic cycles modulo algebraic equivalence to integer cohomology, lifts canonically to a topologically defined quotient of the complex cobordism ring of X. This more refined cycle map gives a topological ... More
Bott vanishing for algebraic surfacesDec 26 2018Mar 01 2019Bott proved a strong vanishing theorem for sheaf cohomology on projective space. It holds for toric varieties, but not for most other varieties. We prove Bott vanishing for the quintic del Pezzo surface, also known as the moduli space M_{0,5}^bar of 5-pointed ... More
HBT Studies with E917 at the AGS: A Status ReportApr 30 1999Two-particle correlations between pions in Au+Au collisions have been measured at beam kinetic energies of 6, 8, and 10.8 GeV/u at the Alternating Gradient Synchrotron (AGS) over a wide range of rapidities using a magnetic spectrometer. The data have ... More
Hypersurfaces that are not stably rationalFeb 13 2015Jun 14 2015We show that a wide class of hypersurfaces in all dimensions are not stably rational. Namely, for all d at least about 2n/3, a very general complex hypersurface of degree d in P^{n+1} is not stably rational. The statement generalizes Colliot-Thelene and ... More
Variance and the Inequality of Arithmetic and Geometric MeansAug 30 2014Aug 27 2015The classical AM-GM inequality has been generalized in a number of ways. Generalizations which incorporate variance appear to be the most useful in economics and finance, as well as mathematically natural. Previous work leaves unanswered the question ... More
Topology of singular algebraic varietiesApr 21 2003I will discuss recent progress by many people in the program of extending natural topological invariants from manifolds to singular spaces. Intersection homology theory and mixed Hodge theory are model examples of such invariants. The past 20 years have ... More
Moduli Dependent mu-Terms in a Heterotic Standard ModelOct 17 2005In this paper, we present a formalism for computing the non-vanishing Higgs mu-terms in a heterotic standard model. This is accomplished by calculating the cubic product of the cohomology groups associated with the vector bundle moduli (phi), Higgs (H) ... More
Non-circular features in Saturn's D ring: D68Jan 23 2014Feb 07 2014D68 is a narrow ringlet located only 67,627 km (1.12 planetary radii) from Saturn's spin axis. Images of this ringlet obtained by the Cassini spacecraft reveal that this ringlet exhibits persistent longitudinal brightness variations and a substantial ... More
The shape and dynamics of a heliotropic dusty ringlet in the Cassini DivisionJun 14 2010Jul 02 2010The so-called "Charming Ringlet" (R/2006 S3) is a low-optical-depth, dusty ringlet located in the Laplace gap in the Cassini Division. This ringlet is particularly interesting because its radial position varies systematically with longitude relative to ... More
Visible Branes with Negative Tension in Heterotic M-TheoryMay 21 2001It is shown that there exist large classes of BPS vacua in heterotic M-theory which have negative tension on the visible orbifold plane, positive tension on the hidden plane and positive tension, physical five-branes in the bulk space. Explicit examples ... More
Experimental studies of 7-cell dual axis asymmetric cavity for energy recovery linacDec 01 2017High average current, transportable energy recovery linacs (ERLs) can be very attractive tools for a number of applications including next generation high-luminosity, compact light sources. Conventional ERLs are based on an electron beam circulating through ... More
From Big Crunch to Big BangAug 24 2001Mar 02 2002We consider conditions under which a universe contracting towards a big crunch can make a transition to an expanding big bang universe. A promising example is 11-dimensional M-theory in which the eleventh dimension collapses, bounces, and re-expands. ... More
Irrationality measure and lower bounds for pi(x)Sep 13 2007Dec 22 2014In this note we show how the irrationality measure of $\zeta(s) = \pi^2/6$ can be used to obtain explicit lower bounds for $\pi(x)$. We analyze the key ingredients of the proof of the finiteness of the irrationality measure, and show how to obtain good ... More
Entangled and disentangled evolution for a single atom in a driven cavitySep 24 2004For an atom in an externally driven cavity, we show that special initial states lead to near-disentangled atom-field evolution, and superpositions of these can lead to near maximally-entangled states. Somewhat counterintutively, we find that (moderate) ... More
Occultations from an active accretion disk in a 72 day detached post-Algol system detected by K2Jan 18 2018Disks in binary systems can cause exotic eclipsing events. MWC 882 (BD-22 4376, EPIC 225300403) is such a disk-eclipsing system identified from observations during Campaign 11 of the K2 mission. We propose that MWC 882 is a post-Algol system with a B7 ... More
Initial study on the shape optimisation of the CLIC crab cavityOct 16 2008The compact linear collider (CLIC) requires a crab cavity to align bunches prior to collision. The bunch structure demands tight amplitude and phase tolerances of the RF fields inside the cavity, for the minimal luminosity loss. Beam loading effects require ... More
Supergravitational Conformal GalileonsMay 18 2017Jul 25 2017The worldvolume actions of 3+1 dimensional bosonic branes embedded in a five-dimensional bulk space can lead to important effective field theories, such as the DBI conformal Galileons, and may, when the Null Energy Condition is violated, play an essential ... More
Pathologies of Factorised Gaussian and MC Dropout Posteriors in Bayesian Neural NetworksSep 02 2019Neural networks provide state-of-the-art performance on a variety of tasks. However, they are often overconfident when making predictions. This inability to properly account for uncertainty limits their application to high-risk decision making, active ... More
Active asteroid (6478) Gault: a blue Q-type surface below the dust?Jul 23 2019We present near-infrared spectroscopy of the sporadically active asteroid (6478) Gault collected on the 3 m NASA/Infrared Telescope Facility observatory in late 2019 March/early April. Long-exposure imaging with the 0.5 m NEEMO T05 telescope and previously ... More
The Lick-Carnegie Exoplanet Survey: Gliese 687b: A Neptune-Mass Planet Orbiting a Nearby Red DwarfMay 12 2014Precision radial velocities from the Automated Planet Finder and Keck/HIRES reveal an M*sin(i) =18 +/- 2 Earth mass planet orbiting the nearby M3V star GJ 687. This planet has an orbital period, P = 38.14 days, and a low orbital eccentricity. Our Stromgren ... More
Symmetric Vacua in Heterotic M-TheoryAug 14 1999Symmetric vacua of heterotic M-theory, characterized by vanishing cohomology classes of individual sources in the three-form Bianchi identity, are analyzed on smooth Calabi-Yau three-folds. We show that such vacua do not exist for elliptically fibered ... More
U-Duality Symmetries from the Membrane WorldvolumeApr 24 1997We study U-duality symmetries of toroidally compactified M theory from the membrane worldvolume point of view. This is done taking the most general set of bosonic background fields into account. Upon restriction to pure moduli backgrounds, we are able ... More
Stabilizing Moduli with a Positive Cosmological Constant in Heterotic M-TheoryMar 10 2006It is shown that strongly coupled heterotic M-theory with anti-five-branes in the S^1/Z_2 bulk space can have meta-stable vacua which break N=1 supersymmetry and have a small, positive cosmological constant. This is demonstrated for the "minimal" heterotic ... More
U-duality Covariant M-theory CosmologySep 03 1997A manifestly U-duality covariant approach to M-theory cosmology is developed and applied to cosmologies in dimensions D=4,5. Cosmological properties such as expansion powers and Hubble parameters turn out to be U-duality invariant in certain asymptotic ... More
Heterotic Kink Solitons and their Worldvolume ActionMay 18 2012We present a formalism for computing the higher-order corrections to the worldvolume action of a co-dimension one kink soliton embedded in five-dimensional heterotic M-theory. The geometry of heterotic M-theory, as well as the effective theory which describes ... More
X-band crab cavities for the CLIC beam delivery systemMar 12 2009The CLIC machine incorporates a 20 mrad crossing angle at the IP to aid the extraction of spent beams. In order to recover the luminosity lost through the crossing angle a crab cavity is proposed to rotate the bunches prior to collision. The crab cavity ... More
Membranes and Three-form SupergravityApr 07 1997We discuss membranes in four-dimensional N=1 superspace. The kappa-invariance of the Green-Schwarz action implies that there is a dual version of N=1 supergravity with a three-form potential. We formulate this new supergravity in terms of a three-form ... More
A candidate super-Earth planet orbiting near the snow line of Barnard's starNov 14 2018Nov 23 2018At a distance of 1.8 parsecs, Barnard's star (Gl 699) is a red dwarf with the largest apparent motion of any known stellar object. It is the closest single star to the Sun, second only to the alpha Centauri triple stellar system. Barnard's star is also ... More
Global Fluctuation Spectra in Big Crunch/Big Bang String VacuaAug 07 2003Sep 01 2003We study Big Crunch/Big Bang cosmologies that correspond to exact world-sheet superconformal field theories of type II strings. The string theory spacetime contains a Big Crunch and a Big Bang cosmology, as well as additional ``whisker'' asymptotic and ... More
Wakefield damping for the CLIC crab cavityJun 19 2009A crab cavity is required in the CLIC to allow effective head-on collision of bunches at the IP. A high operating frequency is preferred as the deflection voltage required for a given rotation angle and the RF phase tolerance for a crab cavity are inversely ... More
A 4-Planet System Orbiting the K0V Star HD 141399Apr 29 2014We present precision radial velocity (RV) data sets from Keck-HIRES and from Lick Observatory's new Automated Planet Finder Telescope and Levy Spectrometer on Mt. Hamilton that reveal a multiple-planet system orbiting the nearby, slightly evolved, K-type ... More
The LCES HIRES/Keck Precision Radial Velocity Exoplanet SurveyFeb 12 2017We describe a 20-year survey carried out by the Lick-Carnegie Exoplanet Survey Team (LCES), using precision radial velocities from HIRES on the Keck-I telescope to find and characterize extrasolar planetary systems orbiting nearby F, G, K, and M dwarf ... More
Olivine-dominated A-type asteroids in the Main Belt: Distribution, Abundance and Relation to FamiliesJan 09 2019Differentiated asteroids are rare in the main asteroid belt despite evidence for ~100 distinct differentiated bodies in the meteorite record. We have sought to understand why so few main-belt asteroids differentiated and where those differentiated bodies ... More
The compositional diversity of non-Vesta basaltic asteroidsMay 17 2017We present near-infrared (0.78-2.45 {\mu}m) reflectance spectra for nine middle and outer main belt (a > 2.5 AU) basaltic asteroids. Three of these objects are spectrally distinct from all classifications in the Bus-DeMeo system and could represent spectral ... More
Two-Dimensional Higher-Derivative Supergravity and a New Mechanism for Supersymmetry BreakingSep 30 1995Dec 29 1996We discuss the general form of quadratic (1,1) supergravity in two dimensions, and show that this theory is equivalent to two scalar supermultiplets coupled to non-trivial supergravity. It is demonstrated that the theory possesses stable vacua with vanishing ... More
Higher-Derivative Gravitation in Bosonic and Superstring TheoriesJun 27 1995Sep 26 1995A discussion of the number of degrees of freedom, and their dynamical properties, in higher-derivative gravitational theories is presented. The complete non-linear sigma model for these degrees of freedom is exhibited using the method of auxiliary fields. ... More
Knots, Braids and BPS States in M-TheoryOct 03 2001In previous work we considered M-theory five branes wrapped on elliptic Calabi-Yau threefold near the smooth part of the discriminant curve. In this paper, we extend that work to compute the light states on the worldvolume of five-branes wrapped on fibers ... More
Five-Brane BPS States in Heterotic M-TheoryMay 12 2000Sep 07 2000We present explicit methods for computing the discriminant curves and the associated Kodaira type fiber degeneracies of elliptically fibered Calabi-Yau threefolds. These methods are applied to a specific three-family, SU(5) grand unified theory of particle ... More
Local Anomaly Cancellation, M-Theory Orbifolds and Phase-TransitionsMay 26 2000Jun 16 2000In this paper we consider orbifold compactifications of M-theory on $S^1/{\bf Z}_2\times T^4/{\bf Z}_2$. We discuss solutions of the local anomaly matching conditions by twisted vector, tensor and hypermultiplets confined on the local orbifold six-planes. ... More
Non-Singular Bouncing Cosmology: Consistency of the Effective DescriptionDec 11 2015We explicitly confirm that spatially flat non-singular bouncing cosmologies make sense as effective theories. The presence of a non-singular bounce in a spatially flat universe implies a temporary violation of the null energy condition, which can be achieved ... More
Non-standard embedding and five-branes in heterotic M-TheoryAug 17 1998Feb 03 1999We construct vacua of M-theory on S^1/Z_2 associated with Calabi-Yau three-folds. These vacua are appropriate for compactification to N=1 supersymmetry theories in both four and five dimensions. We allow for general E_8 x E_8 gauge bundles and for the ... More
The Cosmology of M-Theory and Type II SuperstringsFeb 06 1998We review cosmological solutions of type II superstrings and M-theory, emphasizing the role of non-vanishing Ramond form backgrounds. Compactifications on flat and, more generally, maximally symmetric spatial subspaces are presented. We give a physical ... More
Covariant Harmonic Supergraphity for N = 2 Super Yang--Mills TheoriesOct 06 1998We review the background field method for general N = 2 super Yang-Mills theories formulated in the N = 2 harmonic superspace. The covariant harmonic supergraph technique is then applied to rigorously prove the N=2 non-renormalization theorem as well ... More
Supersymmetric P(X,phi) and the Ghost CondensateDec 16 2010Jun 01 2011We show how to construct supersymmetric actions for higher-derivative scalar field theories of the form P(X,phi), within the context of d=4, N=1 supersymmetry. This construction is of general use, and is applied to write supersymmetric versions of the ... More
Heterotic M-Theory Vacua with Five-BranesMar 16 1999We construct vacua of heterotic M-theory with general gauge bundles and five-branes. Some aspects of the resulting low-energy effective theories are discussed.
Cosmology and Heterotic M-Theory in Five-DimensionsDec 08 1998Dec 11 1998In these lectures, we present cosmological vacuum solutions of Horava-Witten theory and discuss their physical properties. We begin by deriving the five-dimensional effective action of strongly coupled heterotic string theory by performing a reduction, ... More
The Ten-dimensional Effective Action of Strongly Coupled Heterotic String TheoryJan 14 1998Jan 20 1998We derive the ten-dimensional effective action of the strongly coupled heterotic string as the low energy limit of M-theory on S^1/Z_2. In contrast to a conventional dimensional reduction, it is necessary to integrate out nontrivial heavy modes which ... More
Invariant Homology on Standard Model ManifoldsMar 04 2003Torus-fibered Calabi-Yau threefolds Z, with base dP_9 and fundamental group pi_1(Z)=Z_2 X Z_2, are reviewed. It is shown that Z=X/(Z_2 X Z_2), where X=B X_{P_1} B' are elliptically fibered Calabi-Yau threefolds that admit a freely acting Z_2 X Z_2 automorphism ... More
Supersymmetric Sneutrino-Higgs InflationJun 01 2016It is shown that in the phenomenologically realistic supersymmetric $B-L$ MSSM theory, a linear combination of the neutral, up Higgs field with the third family left-and right-handed sneutrinos can play the role of the cosmological inflaton. Assuming ... More
The $R$-parity Violating Decays of Charginos and Neutralinos in the B-L MSSMOct 25 2018Mar 20 2019The $B-L$ MSSM is the MSSM with three right-handed neutrino chiral multiplets and gauged $B-L$ symmetry. The $B-L$ symmetry is broken by the third family right-handed sneutrino acquiring a VEV, thus spontaneously breaking $R$-parity. Within a natural ... More
The $R$-parity Violating Decays of Charginos and Neutralinos in the B-L MSSMOct 25 2018The $B-L$ MSSM is the MSSM with three right-handed neutrino chiral multiplets and gauged $B-L$ symmetry. The $B-L$ symmetry is broken by the third family right-handed sneutrino acquiring a VEV, thus spontaneously breaking $R$-parity. Within a natural ... More
Moduli Spaces of Fivebranes on Elliptic Calabi-Yau ThreefoldsApr 07 1999Apr 08 1999We present a general method for calculating the moduli spaces of fivebranes wrapped on holomorphic curves in elliptically fibered Calabi-Yau threefolds, in particular, in the context of heterotic M theory. The cases of fivebranes wrapped purely on a fiber ... More
The Worldvolume Action of Kink Solitons in AdS SpacetimeMar 20 2012May 18 2012A formalism is presented for computing the higher-order corrections to the worldvolume action of co-dimension one solitons. By modifying its potential, an explicit "kink" solution of a real scalar field in AdS spacetime is found. The formalism is then ... More