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The growth and entrainment of cold gas in a hot windJun 07 2018Jul 24 2018Both absorption and emission line studies show that cold gas around galaxies is commonly outflowing at speeds of several hundred km$\,\textrm{s}^{-1}$. This observational fact poses a severe challenge to our theoretical models of galaxy evolution since ... More

Modeling $237$ Lyman-$α$ spectra of the MUSE-Wide surveySep 20 2017We compare $237$ Lyman-$\alpha$ (Ly$\alpha$) spectra of the "MUSE-Wide survey" (Herenz et al. 2017) to a suite of radiative transfer simulations consisting of a central luminous source within a concentric, moving shell of neutral gas, and dust. This six ... More

Directional Lya equivalent boosting I. Spherically symmetric distributions of clumpsJun 25 2014Aug 29 2014We quantify the directional dependence of the escape fraction of Lyman-$\alpha$ (Ly$\alpha$) and non-ionising UV-continuum photons from a multiphase medium, and investigate whether there exist directional enhancements in the Ly$\alpha$ equivalent width ... More

Giant Lyman-Alpha Nebulae in the Illustris SimulationMay 11 2016Dec 19 2016Several `giant' Lyman-$\alpha$ (Ly$\alpha$) nebulae with extent $\gtrsim 300\,$kpc and observed Ly$\alpha$ luminosity of $\gtrsim 10^{44}\,{\rm erg}\,{\rm s}^{-1}\,{\rm cm}^{-2}\,{\rm arcsec}^{-2}$ have recently been detected, and it has been speculated ... More

Giant Lyman-Alpha Nebulae in the Illustris SimulationMay 11 2016Several `giant' Lyman-$\alpha$ (Ly$\alpha$) nebulae with extent $\gtrsim 300\,$kpc and observed Ly$\alpha$ luminosity of $\gtrsim 10^{44}\,{\rm erg}\,{\rm s}^{-1}\,{\rm cm}^{-2}\,{\rm arcsec}^{-2}$ have recently been detected, and it has been speculated ... More

Ly$α$ Spectra from Multiphase Outflows, and their Connection to Shell ModelsApr 22 2016We perform Lyman-$\alpha$ (Ly$\alpha$) Monte-Carlo radiative transfer calculations on a suite of $2500$ models of multiphase, outflowing media, which are characterized by $14$ parameters. We focus on the Ly$\alpha$ spectra emerging from these media, and ... More

Lyman Radiation Hydrodynamics of Turbulent H II Regions in Molecular Clouds: A Physical Origin of LyC Leakage and the Associated Ly$α$ SpectraMay 07 2019We examine Lyman continuum (LyC) leakage through H II regions regulated by turbulence and radiative feedback in a giant molecular cloud in the context of fully-coupled radiation hydrodynamics (RHD). The physical relations of the LyC escape with H I covering ... More

How cold gas continuously entrains mass and momentum from a hot windJul 10 2019The existence of fast moving, cold gas ubiquitously observed in galactic winds is theoretically puzzling, since the destruction time of cold gas is much smaller than its acceleration time. In Gronke & Oh (2018), we showed that cold gas can accelerate ... More

The LyA-LyC Connection: Evidence for an Enhanced Contribution of UV-faint Galaxies to Cosmic ReionizationApr 27 2016Jul 15 2016The escape of ionizing Lyman Continuum (LyC) photons requires the existence of low-N_HI sightlines, which also promote escape of Lyman-Alpha (Lya). We use a suite of 2500 Lya Monte-Carlo radiative transfer simulations through models of dusty, clumpy interstellar ... More

Lyman Alpha Signatures from Direct Collapse Black HolesFeb 24 2016`Direct collapse black holes' (DCBHs) provide possible seeds for supermassive black holes that exist at redshifts as high as z~7. We study Lyman Alpha (Lya) radiative transfer through simplified representations of the DCBH-scenario. We find that gravitational ... More

A systematic study of Lyman-Alpha transfer through outflowing shells: Model parameter estimationJun 11 2015Oct 15 2015Outflows promote the escape of Lyman-$\alpha$ (Ly$\alpha$) photons from dusty interstellar media. The process of radiative transfer through interstellar outflows is often modelled by a spherically symmetric, geometrically thin shell of gas that scatters ... More

Breaking cosmic degeneracies: Disentangling neutrinos and modified gravity with kinematic informationFeb 05 2019Searches for modified gravity in the large-scale structure try to detect the enhanced amplitude of density fluctuations caused by the fifth force present in many of these theories. Neutrinos, on the other hand, suppress structure growth below their free-streaming ... More

From Mirrors to Windows: Lyman-Alpha Radiative Transfer in a Very Clumpy MediumNov 03 2016Lyman-Alpha (Ly$\alpha$) is the strongest emission line in the Universe and is frequently used to detect and study the most distant galaxies. Because Lya is a resonant line, photons typically scatter prior to escaping; this scattering process complicates ... More

Connecting Faint End Slopes of the Lyman-$α$ emitter and Lyman-break Galaxy Luminosity FunctionsJan 30 2015We predict Lyman-$\alpha$ (Ly$\alpha$) luminosity functions (LFs) of Ly$\alpha$-selected galaxies (Ly$\alpha$ emitters, or LAEs) at $z=3-6$ using the phenomenological model of Dijkstra & Wyithe (2012). This model combines observed UV-LFs of Lyman-break ... More

Cluster mass estimates in screened modified gravitySep 09 2016We use cosmological hydrodynamical simulations to study the effect of screened modified gravity models on the mass estimates of galaxy clusters. In particular, we focus on two novel aspects: (i) we study modified gravity models in which baryons and dark ... More

Blue Wings and Bumps via Fermi-like Acceleration of Lyman-alpha photons across ShocksSep 24 2015We explore the impact of Fermi-like acceleration of Lyman-alpha (Ly{\alpha}) photons across shock fronts on the observed Ly{\alpha} spectral line shape. We first confirm the result of Neufeld & McKee (1988) that this mechanism gives rise to extended blue ... More

Resonant line transfer in a fog: Using Lyman-alpha to probe tiny structures in atomic gasApr 20 2017Motivated by observational and theoretical work which both suggest very small scale ($\lesssim 1\,$pc) structure in the circum-galactic medium of galaxies and in other environments, we study Lyman-$\alpha$ (Ly$\alpha$) radiative transfer in an extremely ... More

The imprint of cosmic ray driven outflow on Lyman-alpha spectraMay 30 2018Jul 20 2018Recent magneto-hydrodynamic simulations of the star-forming interstellar medium (ISM) with parsec scale resolution indicate that relativistic cosmic rays support the launching of galactic outflows on scales of a few kpc. If these fundamental constituents ... More

The Lyman Alpha Reference Sample. VIII. Characterizing Lyman-Alpha Scattering in Nearby GalaxiesNov 08 2017We examine the dust geometry and Ly{\alpha} scattering in the galaxies of the Lyman Alpha Reference Sample (LARS), a set of 14 nearby (0.02 < $z$ < 0.2) Ly{\alpha} emitting and starbursting systems with Hubble Space Telescope Ly{\alpha}, H{\alpha}, and ... More

Halo velocity profiles in screened modified gravity theoriesNov 29 2014Screened modified gravity predicts potentially large signatures in the peculiar velocity field that makes it an interesting probe to test gravity on cosmological scales. We investigate the signatures induced by the Symmetron and a Chameleon $f(R)$ model ... More

Gravitational redshift profiles in the $f(R)$ and symmetron modelsJul 26 2013Dec 11 2013Aims. We investigate the gravitational redshift in clusters of galaxies in the symmetron and Hu-Sawicky $f(R)$ models. The characteristic feature of both models is the screening mechanism that hides the fifth force in dense environments recovering general ... More

Estimates of cluster masses in screened modified gravitySep 09 2016Dec 20 2016We use cosmological hydrodynamical simulations to study the effect of screened modified gravity models on the mass estimates of galaxy clusters. In particular, we focus on two novel aspects: (i) we study modified gravity models in which baryons and dark ... More

Universal predictions of screened modified gravity on cluster scalesMay 26 2015Oct 12 2015Modified gravity models require a screening mechanism to be able to evade the stringent constraints from local gravity experiments and, at the same time, give rise to observable astrophysical and cosmological signatures. Such screened modified gravity ... More

Probing modified gravity in cosmic filamentsJul 19 2018Sep 14 2018Multiple modifications of general relativity (GR) have been proposed in the literature in order to understand the nature of the accelerated expansion of the Universe. However, thus far all the predictions of GR have been confirmed with constantly increasing ... More

Unlocking the Full Potential of Extragalactic Ly$α$ through Its Polarization PropertiesFeb 12 2018Mar 28 2018Lyman-$\alpha$ (Ly$\alpha$) is a powerful astrophysical probe. Not only is it ubiquitous at high redshifts, it is also a resonant line, making Ly$\alpha$ photons scatter. This scattering process depends on the physical conditions of the gas through which ... More

Modelling the gas kinematics of an atypical Lyman-alpha emitting compact dwarf galaxyOct 16 2017Star-forming Compact Dwarf Galaxies (CDGs) resemble the expected pristine conditions of the first galaxies in the Universe and are the best systems to test models on primordial galaxy formation and evolution. Here we report on one of such CDGs, Tololo ... More

Confirmation of double peaked Lyman-alpha emission at z=6.593: Witnessing a galaxy directly contributing to the reionisation of the UniverseMay 29 2018Sep 02 2018Distant luminous Lyman-alpha emitters (LAEs) are excellent targets for spectroscopic observations of galaxies in the epoch of reionisation (EoR). We present deep high-resolution (R=5000) VLT/X-SHOOTER observations, along with an extensive collection of ... More

Green Pea Galaxies Reveal Secrets of Ly$α$ EscapeJun 09 2015Feb 29 2016We analyze archival Ly$\alpha$ spectra of 12 "Green Pea" galaxies observed with the Hubble Space Telescope, model their Ly$\alpha$ profiles with radiative transfer models, and explore the dependence of Ly$\alpha$ escape fraction on various properties. ... More

The Sunburst Arc: Direct Lyman α escape observed in the brightest known lensed galaxyOct 25 2017Nov 19 2017We present rest-frame ultraviolet and optical spectroscopy of the brightest lensed galaxy yet discovered, at redshift z = 2.4. This source reveals a characteristic, triple-peaked Lyman {\alpha} profile which has been predicted by various theoretical works ... More

Search-based Methods to Bound Diagnostic Probabilities in Very Large Belief NetsMar 20 2013Since exact probabilistic inference is intractable in general for large multiply connected belief nets, approximate methods are required. A promising approach is to use heuristic search among hypotheses (instantiations of the network) to find the most ... More

Element Abundances through the Cosmic AgesMar 12 2003The horizon for studies of element abundances has expanded dramatically in the last ten years. Once the domain of astronomers concerned chiefly with stars and nearby galaxies, this field has now become a key component of observational cosmology, as technological ... More

Friendly Artificial Intelligence: the Physics ChallengeSep 02 2014Sep 03 2014Relentless progress in artificial intelligence (AI) is increasingly raising concerns that machines will replace humans on the job market, and perhaps altogether. Eliezer Yudkowski and others have explored the possibility that a promising future for humankind ... More

Cosmological neutrino bounds for non-cosmologistsMar 24 2005I briefly review cosmological bounds on neutrino masses and the underlying gravitational physics at a level appropriate for readers outside the field of cosmology. For the case of three massive neutrinos with standard model freezeout, the current 95% ... More

The importance of quantum decoherence in brain processesJul 05 1999Nov 10 1999Based on a calculation of neural decoherence rates, we argue that that the degrees of freedom of the human brain that relate to cognitive processes should be thought of as a classical rather than quantum system, i.e., that there is nothing fundamentally ... More

The Interpretation of Quantum Mechanics: Many Worlds or Many Words?Sep 15 1997As cutting-edge experiments display ever more extreme forms of non-classical behavior, the prevailing view on the interpretation of quantum mechanics appears to be gradually changing. A (highly unscientific) poll taken at the 1997 UMBC quantum mechanics ... More

On the dimensionality of spacetimeFeb 25 1997Apr 05 1997Some superstring theories have more than one effective low-energy limit, corresponding to classical spacetimes with different dimensionalities. We argue that all but the 3+1-dimensional one might correspond to ``dead worlds'', devoid of observers, in ... More

How to make maps from CMB data without losing informationNov 18 1996Mar 17 1997The next generation of CMB experiments can measure cosmological parameters with unprecedented accuracy - in principle. To achieve this in practice when faced with such gigantic data sets, elaborate data analysis methods are needed to make it computationally ... More

An icosahedron-based method for pixelizing the celestial sphereOct 14 1996For power spectrum estimation it's important that the pixelization of a CMB sky map be smooth and regular to high degree. With this criterion in mind the ``COBE sky cube" was defined. This paper has as central theme to further improve on this elegant ... More

How did it all begin?Aug 20 2005How did it all begin? Although this question has undoubtedly lingered for as long as humans have walked the Earth, the answer still eludes us. Yet since my grandparents were born, scientists have been able to refine this question to a degree I find truly ... More

Dark matter and dark energy from pockets of gravity created by quantum tunneling of the inflaton potentialSep 17 2013Dec 13 2013It is usually assumed that during the reheating period of inflation the inflaton field behaves coherently and follows a classical path. It is pointed out that a background inflaton field \phi_0 falling down a potential density V(\phi) can and frequently ... More

Quantization and SemiclassicsSep 01 2010This course is aimed at graduate students in physics in mathematics and designed to give a comprehensive introduction to Weyl quantization and semiclassics via Egorov's theorem. Chapter 2 gives a quick overview of classical and quantum mechanics on R^d. ... More

Configuration Space Methods and Time Ordering for Scalar Propagators in (Anti and) de Sitter SpacetimesJun 13 2007Aug 29 2007In this master thesis a configuration space method presented by C. Dullemond and E. van Beveren for computing all propagators of a scalar field (Wightman, Hadamard and Schwinger functions,retarded, advanced and Feynman propagator) is reviewed for four-dimensional ... More

Multiple Space Debris Collecting Mission -- Optimal Mission PlanningApr 05 2014This paper addresses the problem of planning successive Space Debris Collecting missions so that they can be achieved at minimal cost by a generic vehicle. The problem mixes combinatorial optimization to select and order the debris among a list of candidates, ... More

Low-Thrust Transfer Between Circular Orbits Using Natural PrecessionMar 02 2015The minimum-fuel low-thrust transfer between circular orbits is formulated using the Edelbaum's averaged dynamics with the addition of the nodal precession due to the first zonal term. The extremal analysis shows that an optimal transfer is composed of ... More

Modified logarithmic Sobolev inequalities for canonical ensemblesJun 06 2013Jun 19 2014In this paper, we prove modified logarithmic Sobolev inequalities for canonical ensembles with superquadratic single-site potential. These inequalities were introduced by Bobkov and Ledoux, and are closely related to concentration of measure and transport-entropy ... More

Twisted K-theory, old and newJan 27 2007Aug 23 2007Twisted K-theory has its origins in the author's PhD thesis [27] : http://www.numdam.org/item?id=ASENS_1968_4_1_2_161_0 and in the paper with P. Donovan http://www.numdam.org/item?id=PMIHES_1970__38__5_0 The objective of this paper is to revisit the subject ... More

Simulating Linear Logic in 1-Only Linear LogicSep 09 2017Linear Logic was introduced by Girard as a resource-sensitive refinement of classical logic. It turned out that full propositional Linear Logic is undecidable (Lincoln, Mitchell, Scedrov, and Shankar) and, hence, it is more expressive than (modalized) ... More

Flat Space Limit of (Higher-Spin) Cardy FormulaAug 29 2014Apr 18 2015In this note I derive the flat space limit of the modified Cardy formula associated with inner horizons and show that it reproduces the correct Galilean conformal field theory counting of flat space cosmology microstates. l also determine the entropy ... More

A Free Boundary Problem for the Parabolic Poisson KernelOct 19 2015We study parabolic chord arc domains, introduced by Hofmann, Lewis and Nystr\"om, and prove a free boundary regularity result below the continuous threshold. More precisely, we show that a Reifenberg flat, parabolic chord arc domain whose Poisson kernel ... More

Genealogical distance under selectionApr 21 2018We study the genealogical distance of two randomly chosen individuals in a population that evolves according to a two type Moran model with mutation and selection. We prove that this distance is stochastically smaller than the corresponding distance in ... More

Two-parameter Asymptotics in Magnetic Weyl CalculusSep 18 2008May 28 2010This paper is concerned with small parameter asymptotics of magnetic quantum systems. In addition to a semiclassical parameter \eps, the case of small coupling $\lambda$ to the magnetic vector potential naturally occurs in this context. Magnetic Weyl ... More

Return Probabilities of Random WalksDec 14 2015Associated to a random walk on $\mathbb{Z}$ and a positive integer $n$, there is a return probability of the random walk returning to the origin after $n$ steps. An interesting question is when the set of return probabilities uniquely determines the random ... More

Error estimates for the finite element approximation of bilinear boundary control problemsJan 11 2019In this article a special class of nonlinear optimal control problems involving a bilinear term in the boundary condition is studied. These kind of problems arise for instance in the identification of an unknown space-dependent Robin coefficient from ... More

Partial flag incidence algebrasMay 05 2016The $n^{th}$ partial flag incidence algebra of a poset $P$ is the set of functions from $P^n$ to some ring which are zero on non-partial flag vectors. These partial flag incidence algebras for $n>2$ are not commutative, not unitary, and not associative. ... More

Fast MLE Computation for the Dirichlet MultinomialMay 01 2014Given a collection of categorical data, we want to find the parameters of a Dirichlet distribution which maximizes the likelihood of that data. Newton's method is typically used for this purpose but current implementations require reading through the ... More

Structure of a condensate for the Bose fluid in a vesselJan 10 2012Mar 09 2014We discuss a possibility of a fragmented structure of the condensate for an interacting Bose systems placed in a vessel. See also Erratum.

Cycles positifs dans les variétés abéliennesSep 12 2011Sep 13 2011In the first part, we study the structure of the R-algebra generated by the Hodge classes on the self-product A^e of a very general principally polarized abelian variety A. In the second part, we compare various notions of positivity for cycles of higher ... More

Improved Measures of Integrated InformationJan 11 2016Jul 18 2016Although there is growing interest in measuring integrated information in computational and cognitive systems, current methods for doing so in practice are computationally unfeasible. Existing and novel integration measures are investigated and classified ... More

How unitary cosmology generalizes thermodynamics and solves the inflationary entropy problemAug 15 2011Aug 15 2012We analyze cosmology assuming unitary quantum mechanics, using a tripartite partition into system, observer and environment degrees of freedom. This generalizes the second law of thermodynamics to "The system's entropy can't decrease unless it interacts ... More

Comparing and combining CMB datasetsSep 01 1998Feb 08 1999One of the best ways of spotting previously undetected systematic errors in CMB experiments is to compare two independent observations of the same region. We derive a set of tools for comparing and combining CMB data sets, applicable also in the common ... More

Removing real-world foregrounds from CMB mapsDec 03 1997Feb 20 1998Most work on foreground removal has treated the case where the frequency dependence of all components is perfectly known and independent of position. In contrast, real-world foregrounds are generally not perfectly correlated between frequencies, with ... More

Measuring cosmological parameters with galaxy surveysJun 19 1997Dec 16 1997We assess the accuracy with which future galaxy surveys can measure cosmological parameters by deriving a handy approximation that we validate numerically. We find that galaxy surveys are quite complementary to future Cosmic Microwave Background (CMB) ... More

CMB mapping experiments: a designer's guideMay 24 1997Jul 29 1997We apply state-of-the art data analysis methods to a number of fictitious CMB mapping experiments, including 1/f noise, distilling the cosmological information from time-ordered data to maps to power spectrum estimates, and find that in all cases, the ... More

Does the universe in fact contain almost no information?Mar 07 1996At first sight, an accurate description of the state of the universe appears to require a mind-bogglingly large and perhaps even infinite amount of information, even if we restrict our attention to a small subsystem such as a rabbit. In this paper, it ... More

A method for extracting maximum resolution power spectra from microwave sky mapsDec 18 1994Jul 25 1996A method for extracting maximal resolution power spectra from microwave sky maps is presented and applied to the 2 year COBE data, yielding a power spectrum that is consistent with a standard n=1, Q=20 micro-Kelvin model. By using weight functions that ... More

The Mathematical UniverseApr 05 2007Oct 08 2007I explore physics implications of the External Reality Hypothesis (ERH) that there exists an external physical reality completely independent of us humans. I argue that with a sufficiently broad definition of mathematics, it implies the Mathematical Universe ... More

Parallel UniversesFeb 07 2003I survey physics theories involving parallel universes, which form a natural four-level hierarchy of multiverses allowing progressively greater diversity. Level I: A generic prediction of inflation is an infinite ergodic universe, which contains Hubble ... More

Cosmological constraints from current CMB and SN 1a data: a brute force 8 parameter analysisSep 16 1998Feb 02 1999We describe constraints on a ``standard'' 8 parameter open cold dark matter (CDM) model from the most recent CMB and SN1a data. Our parameters are the densities of CDM, baryons, vacuum energy and curvature, the reionization optical depth, and the normalization ... More

Doppler peaks and all that: CMB anisotropies and what they can tell usNov 30 1995The power spectrum of fluctuations in the cosmic microwave background (CMB) depends on most of the key cosmological parameters. Accurate future measurements of this power spectrum might therefore allow us to determine h, Omega, Omega_b, Lambda, n, T/S, ... More

ESTIMATING MICROWAVE POWER SPECTRAFeb 06 1995A new method for estimating the power spectrum $C_l$ from cosmic microwave background (CMB) maps was recently presented by the author and applied to the 2 year COBE data. It was found that the spectral resolution $\Delta l$ for COBE could be more than ... More

Dark matter from primordial metric fields and the term (grad g_{00})^2Jul 03 2011It is a well-known truism, inspired on the general theory of relativity, that gravity gravitates. Here we suggest the possibility that dark matter may be caused by the gravitation of the metric. At first sight this seems impossible since the gravitational ... More

From algebraic K-theory to hermitian K-theorySep 26 2005We introduce a new morphism between algebraic and hermitian K-theory. The topological analog is the Adams operation in real K-theory. From this morphism, we deduce a lower bound for the higher algebraic K-theory of a ring A in terms of the classical Witt ... More

Optimal Latent Representations: Distilling Mutual Information into Principal PairsFeb 09 2019Principal component analysis (PCA) is generalized from one to two random vectors, decomposing the correlations between them into a set of "principal pairs" of correlated scalars. For the special case of Gaussian random vectors, PCA decomposes the information ... More

A gradient flow approach to large deviations for diffusion processesMay 15 2014In this work, we investigate links between the formulation of the flow of marginals of reversible diffusion processes as gradient flows in the space of probability measures and path wise large deviation principles for sequences of such processes. An equivalence ... More

Stabilization of the Witt groupSep 27 2005Using an idea due to R.Thomason, we define a "homology theory" on the category of rings which satisfies excision, exactness, homotopy (in the algebraic sense) and periodicity of order 4. For regular noetherian rings, we find P. Balmer's higher Witt groups. ... More

Period and index in the Brauer group of an arithmetic surface (with an appendix by Daniel Krashen)Feb 09 2007May 27 2009In this paper we introduce two new ways to split ramification of Brauer classes on surfaces using stacks. Each splitting method gives rise to a new moduli space of twisted stacky vector bundles. By studying the structure of these spaces we prove new results ... More

Numerical Solution of the Simple Monge-Ampère Equation with Non-convex Dirichlet Data on Non-convex DomainsMay 12 2017Jun 01 2017The existence of a unique numerical solution of the semi-Lagrangian method for the simple Monge-Amp\`ere equation is known independently of the convexity of the domain or Dirichlet boundary data -- when the Monge-Amp\`ere equation is posed as Bellman ... More

A Two-Phase Free Boundary Problem for Harmonic MeasureSep 15 2014Sep 27 2016We study a 2-phase free boundary problem for harmonic measure first considered by Kenig and Toro and prove a sharp H\"older regularity result. The central difficulty is that there is no a priori non-degeneracy in the free boundary condition. Thus we must ... More

Compactified moduli of projective bundlesJun 11 2007May 25 2009We present a method for compactifying stacks of $\PGL_n$-torsors (Azumaya algebras) on algebraic spaces. In particular, when the ambient space is a smooth projective surface we use our methods to show that various moduli spaces are irreducible and carry ... More

General Boundary Quantum Field Theory in Anti de Sitter SpacetimesFeb 03 2016Jun 09 2016We mainly study real Klein-Gordon theory on Anti de Sitter spacetimes, and apply the General Boundary Formulation (GBF) of Quantum Theory in order to compute a radial S-matrix. We consider first the classical theory, giving a complete list of Klein-Gordon ... More

Family size decomposition of genealogical treesMar 07 2019We study the path of family size decompositions of varying depth of genealogical trees. We prove that this decomposition as a function on (equivalence classes of) ultra-metric measure spaces to the Skorohod space describing the family sizes at different ... More

Ly$α$ profile, dust, and prediction of Ly$α$ escape fraction in Green Pea GalaxiesJan 07 2017Jul 27 2017We studied Lyman-$\alpha$ (Ly$\alpha$) escape in a statistical sample of 43 Green Peas with HST/COS Ly$\alpha$ spectra. Green Peas are nearby star-forming galaxies with strong [OIII]$\lambda$5007 emission lines. Our sample is four times larger than the ... More

Hubble captures multiply-imaged ionizing radiation from strongly lensed galaxy at z=2.4Apr 17 2019Apr 18 2019The early Universe was ionized by hard ultraviolet radiation from hot, young stars in the first galaxies. These galaxies contain absorbing neutral Hydrogen which must be configured favorably to allow ionizing escape; only a few dozen cases have been detected ... More

A zero point energy explanation of a peak in liquid helium's dynamic structure factorMay 27 1997Recent high resolution experiments show a strong peak at Q = 1.9 Ang^{-1} in liquid helium's dynamic structure factor that exhibits a singular dependence on temperature. The theoretical situation is briefly reviewed, and the comment is made that the simplest ... More

Towards a q-analogue of the Harer-Zagier formula via rook placementsDec 10 2014In 1986 Harer and Zagier computed a certain matrix integral to determine an influential closed-form formula for the number of (orientable) one-face maps on n vertices colored from N colors. Kerov (1997) provided a proof which computed the same matrix ... More

Abelian gauge symmetries and fluxed instantons in compactifications of type IIB and F-theoryFeb 15 2014We discuss the role of Abelian gauge symmetries in type IIB orientifold compactifications and their F-theory uplift. Particular emphasis is placed on U(1)s which become massive through the geometric St\"uckelberg mechanism in type IIB. We present a proposal ... More

On Regularity of J-holomorphic MapsSep 03 2014We provide a short proof that an $L^2_1$ and $J$-holomorphic curve is in fact smooth. As an application, we deduce a removal of singularity theorem for curves of finite energy.

Exploiting the Statistics of Learning and InferenceFeb 26 2014Mar 04 2014When dealing with datasets containing a billion instances or with simulations that require a supercomputer to execute, computational resources become part of the equation. We can improve the efficiency of learning and inference by exploiting their inherent ... More

Practical Issues in Constructing a Bayes' Belief NetworkMar 27 2013Bayes belief networks and influence diagrams are tools for constructing coherent probabilistic representations of uncertain knowledge. The process of constructing such a network to represent an expert's knowledge is used to illustrate a variety of techniques ... More

The First Galaxies: Clues from Element AbundancesJan 06 2000It has recently become possible to measure directly the abundances of several chemical elements in a variety of environments at redshifts up to z = 5. In this review I summarise the latest observations of Lyman break galaxies, damped Lyman alpha systems ... More

Deuterium at High Redshifts: Recent Advances and Open IssuesJan 19 2006Among the light elements created in the Big Bang, deuterium is one of the most difficult to detect but is also the one whose abundance depends most sensitively on the density of baryons. Thus, although we still have only a few positive identifications ... More

How to measure CMB power spectra without losing informationNov 21 1996Mar 12 1997A new method for estimating the angular power spectrum C_l from cosmic microwave background (CMB) maps is presented, which has the following desirable properties: (1) It is unbeatable in the sense that no other method can measure C_l with smaller error ... More

Nuclear War from a Cosmic PerspectiveMay 01 2015May 21 2015I discuss the impact of computer progress on nuclear war policy, both by enabling more accurate nuclear winter simulations and by affecting the probability of war starting accidentally. I argue that from a cosmic perspective, humanity's track record of ... More

What does inflation really predict?Oct 12 2004Mar 11 2005If the inflaton potential has multiple minima, as may be expected in, e.g., the string theory "landscape", inflation predicts a probability distribution for the cosmological parameters describing spatial curvature (Omega_tot), dark energy (rho_Lambda, ... More

Rational curves in the moduli of supersingular K3 surfacesJul 30 2015We show how to construct non-isotrivial families of supersingular K3 surfaces over rational curves using a relative form of the Artin-Tate isomorphism and twisted analogues of Bridgeland's results on moduli spaces of stable sheaves on elliptic surfaces. ... More

Differential Equations of Mathematical PhysicsAug 16 2015These lecture notes for the course APM 351 at the University of Toronto are aimed at mathematicians and physicists alike. It is not meant as an introductory course to PDEs, but rather gives an overview of how to view and solve differential equations that ... More

The Large Hadron Electron Collider ProjectAug 20 2009A Conceptual Design Report (CDR) for the Large Hadron Electron Collider, the LHeC, is being prepared, to which an introduction was given for the plenary panel discussion on the future of deep inelastic scattering held at DIS09. This is briefly summarised ... More

Twisted bundles and twisted K-theoryDec 12 2010We offer here a more direct approach to twisted K-theory, based on the notion of twisted vector bundles (of finite or infinite dimension) and of twisted principal bundles. This is closeely related to the classical notion ot torsors and bundles of modules ... More

Le theoreme de periodicite en K-theorie hermitienneOct 26 2008Bott periodicity plays an important role in topological K-theory. The purpose of this paper is to extend the periodicity theorem in a discrete context, where all classical groups are involved and not just the general linear group. The present paper generalizes ... More

Clifford modules and twisted K-theoryJan 17 2008The purpose of this shord paper is to make the link between the fundamental work of Atiyah, Bott and Shapiro (MR0167985/29/5250) and twisted K-theory (MR0282363/43/8075). This link was implicit for a long time in the literature (for the description of ... More