Publications (155)373.85 Total impact
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ABSTRACT: Holography grew out of black hole thermodynamics, which relies on the causal structure and general covariance of general relativity. In Einstein{\ae}ther theory, a generally covariant theory with a dynamical timelike unit vector, every solution breaks local Lorentz invariance, thereby grossly modifying the causal structure of gravity. However, there are still absolute causal boundaries, called "universal horizons", which are not Killing horizons yet obey a first law of black hole mechanics and must have an entropy if they do not violate a generalized second law. We couple a scalar field to the timelike vector and show via the tunneling approach that the universal horizon radiates as a blackbody at a fixed temperature, even if the scalar field equations also violate local Lorentz invariance. This suggests that the class of holographic theories may be much broader than currently assumed.  [Show abstract] [Hide abstract]
ABSTRACT: We show that nonSpin cycles in type IIB CalabiYau orientifold compactifications with vanishing B field naturally support orientifoldinvariant Dbrane instantons. These instantons, associated to the holomorphic cotangent bundle of the nonSpin cycle, can lead to nonperturbative corrections to the superpotential. 
Article: Mechanics of universal horizons
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ABSTRACT: Modified gravity models such as Ho\v{r}avaLifshitz gravity or Einstein{\ae}ther theory violate local Lorentz invariance and therefore destroy the notion of a universal light cone. Despite this, in the infrared limit both models above possess static, spherically symmetric solutions with "universal horizons"  hypersurfaces that are causal boundaries between an interior region and asymptotic spatial infinity. In other words, there still exist black hole solutions. We construct a Smarr formula (the relationship between the total energy of the spacetime and the area of the horizon) for such a horizon in Einstein{\ae}ther theory. We further show that a slightly modified first law of black hole mechanics still holds with the relevant area now a crosssection of the universal horizon. We construct new analytic solutions for certain Einstein{\ae}ther Lagrangians and illustrate how our results work in these exact cases. Our results suggest that holography may be extended to these theories despite the very different causal structure as long as the universal horizon remains the unique causal boundary when matter fields are added.  [Show abstract] [Hide abstract]
ABSTRACT: We describe how local toric singularities, including the Toric Lego construction, can be embedded in compact CalabiYau manifolds. We study in detail the addition of Dbranes, including noncompact flavor branes as typically used in semirealistic model building. The global geometry provides constraints on allowable local models. As an illustration of our discussion we focus on D3 and D7branes on (the partially resolved) (dP0)^3 singularity, its embedding in a specific CalabiYau manifold as a hypersurface in a toric variety, the related type IIB orientifold compactification, as well as the corresponding Ftheory uplift. Our techniques generalize naturally to complete intersections, and to a large class of Ftheory backgrounds with singularities.  [Show abstract] [Hide abstract]
ABSTRACT: We study electromagnetically charged dilatonic black brane solutions in arbitrary dimensions with flat transverse spaces, that are asymptotically AdS. This class of solutions includes spacetimes which possess a bulk region where the metric is approximately invariant under Lifshitz scalings. Given fixed asymptotic boundary conditions, we analyze how the behavior of the bulk up to the horizon varies with the charges and derive the extremality conditions for these spacetimes.  [Show abstract] [Hide abstract]
ABSTRACT: We study nongaussianity effects, using the $\delta N$ formalism, in a multifield inflationary model consisting of K\"ahler moduli derived from type IIB string compactification in the large volume limit. The analytical work in this paper mostly follows the separable potential method developed by Vernizzi and Wands. The numerical analysis is then used in computing nongaussianity beyond slowroll regime. The possibility of the curvaton scenario is also discussed. We give the condition for the existence of the curvaton and calculate the nonguassianity generated by the curvaton decay in the large volume limit. Comment: 25 pages  [Show abstract] [Hide abstract]
ABSTRACT: We construct a multifield inflationary model consisting of multiple K\"ahler moduli derived from type IIB string compactification in the large volume limit. The model consists of both heavy and light fields, with the former being frozen during the inflationary period and the latter acting as the inflaton(s). We study the evolution of all the fields during and after inflation until the preheating era when all the fields oscillate around their vacuum expectation values. Our numerical analysis shows that the curvature perturbations have an almost scale invariant power spectrum with $n_s \simeq 0.96$. Comment: 25 pages, 17 figures  [Show abstract] [Hide abstract]
ABSTRACT: Within the context of local type IIB models arising from branes at toric CalabiYau singularities, we present a systematic way of joining any number of desired sectors into a consistent theory. The different sectors interact via massive messengers with masses controlled by tunable parameters. We apply this method to a toy model of the minimal supersymmetric standard model (MSSM) interacting via gauge mediation with a metastable supersymmetry breaking sector and an interacting dark matter sector. We discuss how a mirror procedure can be applied in the type IIA case, allowing us to join certain intersecting brane configurations through massive mediators. 
Article: Topology from Cosmology
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ABSTRACT: We show that cosmological observables can constrain the topology of the compact additional dimensions predicted by string theory. To do this, we develop a general strategy for relating cosmological observables to the microscopic parameters of the potentials and fielddependent kinetic terms of the multiple scalar fields that arise in the lowenergy limit of string theory. We apply this formalism to the Large Volume Scenarios in Type IIB flux compactifications where analytical calculations are possible. Our methods generalize to other settings. 
Article: The COMPASS experiment at CERN

Article: The COMPASS experiment at CERN
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ABSTRACT: The COMPASS experiment makes use of the CERN SPS highintensitymuon and hadron beams for the investigation of the nucleon spin structure and the spectroscopy of hadrons. One or more outgoing particles are detected in coincidence with the incoming muon or hadron. A large polarized target inside a superconducting solenoid is used for the measurements with the muon beam. Outgoing particles are detected by a twostage, large angle and large momentum range spectrometer. The setup is built using several types of tracking detectors, according to the expected incident rate, required space resolution and the solid angle to be covered. Particle identification is achieved using a RICH counter and both hadron and electromagnetic calorimeters. The setup has been successfully operated from 2002 onwards using a muon beam. Data with a hadron beam were also collected in 2004. This article describes the main features and performances of the spectrometer in 2004; a short summary of the 2006 upgrade is also given.  [Show abstract] [Hide abstract]
ABSTRACT: We present a precise measurement of the deuteron longitudinal spin asymmetry $A_1^d$ and of the deuteron spindependent structure function $g_1^d$ at $Q^2 < $ 1~(GeV/$c$)$^2$ and $4\cdot$10$^{5} < x < $~2.5$\cdot$10$^{2}$ based on the data collected by the COMPASS experiment at CERN during the years 2002 and 2003. The statistical precision is tenfold better than that of the previous measurement in this region. The measured $A_1^d$ and $g_1^d$ are found to be consistent with zero in the whole range of $x$. 

Article: A new measurement of the Collins and Sivers asymmetries on a transversely polarised deuteron target
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ABSTRACT: New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deepinelastic scattering of muons on a transversely polarised 6LiD target are presented. The data were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with naive expectations and with existing model calculations.  [Show abstract] [Hide abstract]
ABSTRACT: A fourdimensional universe, arising from a flux compactification of Type IIB string theory, contains scalar fields with a potential determined by topological and geometric parameters of the internal hidden dimensions. We show that inflation can be realized via rolling towards the large internal volume minima that are generic in these scenarios, and we give explicit formulae relating the microscopic parameters (e.g., the Euler number of the internal space) to the cosmological observables (e.g., the spectral index). We find that the tensortoscalar ratio, the running of the spectral index, and the potential energy density at the minimum are related by consistency relations and are exponentially small in the number of efoldings. Further, requiring that these models arise as lowenergy limits of string theory eliminates most of them, even if they are phenomenologically valid. In this context, this approach provides a strategy for systematically falsifying stringy inflation models.  [Show abstract] [Hide abstract]
ABSTRACT: We present a determination of the gluon polarization ΔG/G in the nucleon, based on the helicity asymmetry of quasireal photoproduction events, Q2<1 2(GeV/c), with a pair of large transversemomentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6LiD target. The helicity asymmetry for the selected events is 〈A∥/D〉=0.002±0.019(stat)±0.003(syst). From this value, we obtain in a leadingorder QCD analysis ΔG/G=0.024±0.089(stat)±0.057(syst) at xg=0.095 and μ2≃3 2(GeV/c).  [Show abstract] [Hide abstract]
ABSTRACT: We present a determination of the gluon polarization Delta G/G in the nucleon, based on the helicity asymmetry of quasireal photoproduction events, Q^2<1(GeV/c)^2, with a pair of large transversemomentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6LiD target. The helicity asymmetry for the selected events is <A_/D> = 0.002 + 0.019(stat.) + 0.003(syst.). From this value, we obtain in a leadingorder QCD analysis Delta G/G=0.024 + 0.089(stat.) + 0.057(syst.) at x_g = 0.095 and mu^2 =~ 3 (GeV}/c)^2. 
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ABSTRACT: We develop several nonperturbative approximations for studying the dynamics of a supersymmetric O(N) model which preserve supersymmetry. We study the phase structure of the vacuum in both the leading order in largeN approximation as well as in the Hartree approximation, and derive the finite temperature renormalized effective potential. We derive the exact SchwingerDyson equations for the superfield Green functions and develop the machinery for going beyond the next to leading order in largeN approximation using a truncation of these equations which can also be derived from a twoparticle irreducible effective action. Comment: 16 pages, 3 figures  [Show abstract] [Hide abstract]
ABSTRACT: First measurements of the Collins and Sivers asymmetries of charged hadrons produced in deepinelastic scattering of muons on a transversely polarized 6LiD target are presented. The data were taken in 2002 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. The Collins asymmetry turns out to be compatible with zero, as does the measured Sivers asymmetry within the present statistical errors.
Publication Stats
4k  Citations  
373.85  Total Impact Points  
Top Journals
Institutions

20042012

University of New Hampshire
 Department of Physics
Durham, New Hampshire, United States


19972007

Bielefeld University
Bielefeld, North RhineWestphalia, Germany


19962006

University of Helsinki
Helsinki, Uusimaa, Finland


20002002

University of Southern California
 Department of Physics and Astronomy
Los Angeles, California, United States 
University of Florence
Florens, Tuscany, Italy


19932000

University of California, Santa Barbara
 Kavli Institute for Theoretical Physics
Santa Barbara, California, United States 
Université de Neuchâtel
 Institut de physique (IPH)
Neuenburg, Neuchâtel, Switzerland


19921998

CERN
 Physics Department (PH)
Genève, Geneva, Switzerland


1994

Yale University
 Department of Physics
New Haven, Connecticut, United States 
University of Houston
 Department of Physics
Houston, Texas, United States 
University of Freiburg
Freiburg, BadenWürttemberg, Germany


19911992

University of Texas at Austin
 Department of Physics
Austin, Texas, United States
