Showing papers in "Journal of High Energy Physics in 2008"
TL;DR: The anti-k-t algorithm as mentioned in this paper behaves like an idealised cone algorithm, in that jets with only soft fragmentation are conical, active and passive areas are equal, the area anomalous dimensions are zero, the non-global logarithms are those of a rigid boundary and the Milan factor is universal.
Abstract: The k_t and Cambridge/Aachen inclusive jet finding algorithms for hadron-hadron collisions can be seen as belonging to a broader class of sequential recombination jet algorithms, parametrised by the power of the energy scale in the distance measure. We examine some properties of a new member of this class, for which the power is negative. This ``anti-k_t'' algorithm essentially behaves like an idealised cone algorithm, in that jets with only soft fragmentation are conical, active and passive areas are equal, the area anomalous dimensions are zero, the non-global logarithms are those of a rigid boundary and the Milan factor is universal. None of these properties hold for existing sequential recombination algorithms, nor for cone algorithms with split--merge steps, such as SISCone. They are however the identifying characteristics of the collinear unsafe plain ``iterative cone'' algorithm, for which the anti-k_t algorithm provides a natural, fast, infrared and collinear safe replacement.
5,740 citations
TL;DR: In this paper, the authors constructed three dimensional Chern-Simons-matter theories with gauge groups U(N) × U(n) and SU(N), SU(2) × SU (2) which have explicit = 6 superconformal symmetry.
Abstract: We construct three dimensional Chern-Simons-matter theories with gauge groups U(N) × U(N) and SU(N) × SU(N) which have explicit = 6 superconformal symmetry. Using brane constructions we argue that the U(N) × U(N) theory at level k describes the low energy limit of N M2-branes probing a C4/Zk singularity. At large N the theory is then dual to M-theory on AdS4 × S7/Zk. The theory also has a 't Hooft limit (of large N with a fixed ratio N/k) which is dual to type IIA string theory on AdS4 × CP3. For k = 1 the theory is conjectured to describe N M2-branes in flat space, although our construction realizes explicitly only six of the eight supersymmetries. We give some evidence for this conjecture, which is similar to the evidence for mirror symmetry in d = 3 gauge theories. When the gauge group is SU(2) × SU(2) our theory has extra symmetries and becomes identical to the Bagger-Lambert theory.
3,091 citations
TL;DR: In this article, a derivation of the nonlinear equations of boundary fluid dynamics from gravity from gravity is presented, with specific values for fluid parameters, and an explicit expression for the expansion of this fluid stress tensor including terms up to second order in the derivative expansion.
Abstract: Black branes in AdS5 appear in a four parameter family labeled by their velocity and temperature. Promoting these parameters to Goldstone modes or collective coordinate fields—arbitrary functions of the coordinates on the boundary of AdS5—we use Einstein's equations together with regularity requirements and boundary conditions to determine their dynamics. The resultant equations turn out to be those of boundary fluid dynamics, with specific values for fluid parameters. Our analysis is perturbative in the boundary derivative expansion but is valid for arbitrary amplitudes. Our work may be regarded as a derivation of the nonlinear equations of boundary fluid dynamics from gravity. As a concrete application we find an explicit expression for the expansion of this fluid stress tensor including terms up to second order in the derivative expansion.
1,361 citations
TL;DR: The effective field theory of inflation as discussed by the authors is the most general theory describing the fluctuations around a quasi de Sitter background, in the case of single field models, in which the scalar mode can be eaten by the metric by going to unitary gauge.
Abstract: We study the effective field theory of inflation, i.e. the most general theory describing the fluctuations around a quasi de Sitter background, in the case of single field models. The scalar mode can be eaten by the metric by going to unitary gauge. In this gauge, the most general theory is built with the lowest dimension operators invariant under spatial diffeomorphisms, like g00 and Kμν, the extrinsic curvature of constant time surfaces. This approach allows us to characterize all the possible high energy corrections to simple slow-roll inflation, whose sizes are constrained by experiments. Also, it describes in a common language all single field models, including those with a small speed of sound and Ghost Inflation, and it makes explicit the implications of having a quasi de Sitter background. The non-linear realization of time diffeomorphisms forces correlation among different observables, like a reduced speed of sound and an enhanced level of non-Gaussianity.
1,183 citations
TL;DR: In this article, a theory-independent inequality [phi(2)] 1 was derived for 4D conformal fixed points, where f(d) = 2 + O(root d - 1), which shows that the free theory limit is approached continuously.
Abstract: In an arbitrary unitary 4D CFT we consider a scalar operator phi, and the operator phi(2) defined as the lowest dimension scalar which appears in the OPE phi x phi with a nonzero coefficient. Using general considerations of OPE, conformal block decomposition, and crossing symmetry, we derive a theory-independent inequality [phi(2)] 1 we have f(d) = 2 + O(root d - 1), which shows that the free theory limit is approached continuously. We perform some checks of our bound. We find that the bound is satisfied by all weakly coupled 4D conformal fixed points that we are able to construct. The Wilson-Fischer fixed points violate the bound by a constant O( 1) factor, which must be due to the subtleties of extrapolating to 4 - epsilon dimensions. We use our method to derive an analogous bound in 2D, and check that the Minimal Models satisfy the bound, with the Ising model nearly-saturating it. Derivation of an analogous bound in 3D is currently not feasible because the explicit conformal blocks are not known in odd dimensions. We also discuss the main phenomenological motivation for studying this set of questions: constructing models of dynamical ElectroWeak Symmetry Breaking without flavor problems.
1,097 citations
TL;DR: In this article, the second-order viscous hydrodynamics in conformal field theories at finite temperature was considered and conformal invariance imposes powerful constraints on the form of second-orders corrections.
Abstract: We consider second-order viscous hydrodynamics in conformal field theories at finite temperature. We show that conformal invariance imposes powerful constraints on the form of the second-order corrections. By matching to the AdS/CFT calculations of correlators, and to recent results for Bjorken flow obtained by Heller and Janik, we find three (out of five) second-order transport coefficients in the strongly coupled = 4 supersymmetric Yang-Mills theory. We also discuss how these new coefficents can arise within the kinetic theory of weakly coupled conformal plasmas. We point out that the Muller-Israel-Stewart theory, often used in numerical simulations, does not contain all allowed second-order terms and, frequently, terms required by conformal invariance.
850 citations
TL;DR: In this article, the authors studied the correlation functions of the energies deposited on calorimeters placed at a large distance from the colliders and showed that the small angle singularities of energy correlation functions are controlled by the twist of nonlocal light-ray operators with a definite spin.
Abstract: We study observables in a conformal field theory which are very closely related to the ones used to describe hadronic events at colliders. We focus on the correlation functions of the energies deposited on calorimeters placed at a large distance from the collision. We consider initial states produced by an operator insertion and we study some general properties of the energy correlation functions for conformal field theories. We argue that the small angle singularities of energy correlation functions are controlled by the twist of non-local light-ray operators with a definite spin. We relate the charge two point function to a particular moment of the parton distribution functions appearing in deep inelastic scattering. The one point energy correlation functions are characterized by a few numbers. For = 1 superconformal theories the one point function for states created by the R-current or the stress tensor are determined by the two parameters a and c characterizing the conformal anomaly. Demanding that the measured energies are positive we get bounds on a/c. We also give a prescription for computing the energy and charge correlation functions in theories that have a gravity dual. The prescription amounts to probing the falling string state as it crosses the AdS horizon with gravitational shock waves. In the leading, two derivative, gravity approximation the energy is uniformly distributed on the sphere at infinity, with no fluctuations. We compute the stringy corrections and we show that they lead to small, non-gaussian, fluctuations in the energy distribution. Corrections to the one point functions or antenna patterns are related to higher derivative corrections in the bulk.
811 citations
TL;DR: In this paper, the authors examined several physical predictions of this model and showed that they are in agreement with expected M2-brane dynamics, including quantization of the Chern-Simons coefficient, the vacuum moduli space, a massive deformation leading to fuzzy three-sphere vacua, and a possible large n limit.
Abstract: Recently a three-dimensional field theory was derived that is consistent with all the symmetries expected of the worldvolume action for multiple M2-branes. In this note we examine several physical predictions of this model and show that they are in agreement with expected M2-brane dynamics. In particular, we discuss the quantization of the Chern-Simons coefficient, the vacuum moduli space, a massive deformation leading to fuzzy three-sphere vacua, and a possible large n limit. In this large n limit, the fuzzy funnel solution correctly reproduces the mass of an M5-brane.
787 citations
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TL;DR: In this article, two generalizations of the = 6 superconformal Chern-Simons-matter theories with gauge group U(n) × U(N) have been considered, and they are conjectured to describe M−N| fractional M2-branes localized at the orbifold singularity.
Abstract: We consider two generalizations of the = 6 superconformal Chern-Simons-matter theories with gauge group U(N) × U(N). The first generalization is to = 6 superconformal U(M) × U(N) theories, and the second to = 5 superconformal O(2M) × USp(2N) and O(2M+1) × USp(2N) theories. These theories are conjectured to describe M2-branes probing C4/Zk in the unitary case, and C4/k in the orthogonal/symplectic case, together with a discrete flux, which can be interpreted as |M−N| fractional M2-branes localized at the orbifold singularity. The classical theories with these gauge groups have been constructed before; in this paper we focus on some quantum aspects of these theories, and on a detailed description of their M theory and type IIA string theory duals.
764 citations
TL;DR: In this article, the authors established a theoretical grounding for the discussion of jet areas, introducing two main definitions, passive and active areas, which respectively characterise the sensitivity to pointlike or diffuse pileup and UE radiation.
Abstract: The area of a jet is a measure of its susceptibility to radiation, like pileup or underlying event (UE), that on average, in the jet’s neighbourhood, is uniform in rapidity and azimuth. In this article we establish a theoretical grounding for the discussion of jet areas, introducing two main definitions, passive and active areas, which respectively characterise the sensitivity to pointlike or diffuse pileup and UE radiation. We investigate the properties of jet areas for three standard jet algorithms, kt, Cambridge/Aachen and SISCone. Passive areas for single-particle jets are equal to the naive geometrical expectation πR 2 , but acquire an anomalous dimension at higher orders in the coupling, calculated here at leading order. The more physically relevant active areas differ from πR 2 even for single-particle jets, substantially so in the case of the cone algorithms like SISCone with a Tevatron Run-II split–merge procedure. We compare our results with direct measures of areas in parton-shower Monte Carlo simulations and find good agreement with the main features of the analytical predictions. We furthermore justify the use of jet areas to subtract the contamination from pileup.
704 citations
TL;DR: In this paper, the implementation of a new parton shower model based on the Catani-Seymour dipole factorisation, as first suggested by [1,?2], is discussed.
Abstract: In this publication the implementation of a new parton shower model based on the Catani-Seymour dipole factorisation, as first suggested by [1,?2], is discussed. First results obtained with the new algorithm are compared with experimental data.
TL;DR: A new tree-level matrix element generator, based on the color dressed Berends-Giele recursive relations, is presented, dedicated to be used with large multiplicities and color sampling.
Abstract: We present a new tree-level matrix element generator, based on the color dressed Berends-Giele recursive relations. We discuss two new algorithms for phase space integration, dedicated to be used with large multiplicities and color sampling.
TL;DR: In this paper, a gravity theory in five dimensions coupled to a dilaton and an axion may capture the important qualitative features of pure YM theory, and a part of the effects of higher α'-corrections is resummed into a Dilaton potential, which determines the full structure of the vacuum solution.
Abstract: Various holographic approaches to QCD in five dimensions are explored using input both from the putative five-dimensional non-critical string theory as well as QCD. It is argued that a gravity theory in five dimensions coupled to a dilaton and an axion may capture the important qualitative features of pure YM theory. A part of the effects of higher α'-corrections is resummed into a dilaton potential. The potential is shown to be in one-to-one correspondence with the exact β-function of QCD, and its knowledge determines the full structure of the vacuum solution. The geometry near the UV boundary is that of AdS5 with logarithmic corrections reflecting the asymptotic freedom of QCD. We find that all relevant confining backgrounds have an IR singularity of the ``good" kind that allows unambiguous spectrum computations. Near the singularity the 't Hooft coupling is driven to infinity. Asymptotically linear glueball masses can also be achieved. The classification of all confining asymptotics, the associated glueball spectra and meson dynamics are addressed in a companion paper arXiv:0707.1349
TL;DR: In this paper, the Wt single-top production channel to next-to-leading order in QCD, interfaced with parton showers within the MC@NLO formalism, is presented.
Abstract: We present the calculation of the Wt single-top production channel to next-to-leading order in QCD, interfaced with parton showers within the MC@NLO formalism. This channel provides a complementary way of investigating the properties of the Wtb vertex, with respect to the s- and t-channels. We pay special attention to the separation of this process from top quark pair production.
TL;DR: In this article, a grand unified model based on SUSY SU(5) in extra dimensions and on the flavour group A4 × U(1) was proposed to reproduce tri-bimaximal mixing for neutrinos with the accuracy required by the data, also leading to a natural description of the observed pattern of quark masses and mixings.
Abstract: We discuss a grand unified model based on SUSY SU(5) in extra dimensions and on the flavour group A4 × U(1) which, besides reproducing tri-bimaximal mixing for neutrinos with the accuracy required by the data, also leads to a natural description of the observed pattern of quark masses and mixings.
TL;DR: The recently developed algorithm FIRE performs the reduction of Feynman integrals to master integrals based on a number of strategies, such as applying the Laporta algorithm, the s-bases algorithm, region-Bases and integrating explicitly over loop momenta when possible.
Abstract: The recently developed algorithm FIRE performs the reduction of Feynman integrals to master integrals. It is based on a number of strategies, such as applying the Laporta algorithm, the s-bases algorithm, region-bases and integrating explicitly over loop momenta when possible. Currently it is being used in complicated three-loop calculations.
TL;DR: In this article, the Yang-Mills equations are solved in an AdS4-Schwarzschild background with superconductivity, where the order parameter is a vector and the conductivities are strongly anisotropic.
Abstract: We construct black hole solutions to the Yang-Mills equations in an AdS4-Schwarzschild background which exhibit superconductivity. What makes these backgrounds p-wave superconductors is that the order parameter is a vector, and the conductivities are strongly anisotropic in a manner that is suggestive of a gap with nodes. The low-lying excitations of the normal state have a relaxation time which grows rapidly as the temperature decreases, consistent with the absence of impurity scattering. A numerical exploration of quasinormal modes close to the transition temperature suggests that p-wave backgrounds are stable against perturbations analogous to turning on a p+ip gap, whereas p+ip-wave configurations are unstable against turning into pure p-wave backgrounds.
TL;DR: In this article, three dimensional Einstein gravity with negative cosmological constant 1/?2 deformed by a gravitational Chern-Simons action with coefficient 1/? is studied in an asymptotically AdS3 spacetime.
Abstract: Three dimensional Einstein gravity with negative cosmological constant ?1/?2 deformed by a gravitational Chern-Simons action with coefficient 1/? is studied in an asymptotically AdS3 spacetime. It is argued to violate unitary or positivity for generic ? due to negative-energy massive gravitons. However at the critical value ?? = 1, the massive gravitons disappear and BTZ black holes all have mass and angular momentum related by ?M = J. The corresponding chiral quantum theory of gravity is conjectured to exist and be dual to a purely right-moving boundary CFT with central charges (cL,?cR) = (0,?3?/G).
TL;DR: A program that implements the OPP reduction method to extract the coefficients of the one-loop scalar integrals from a user defined (sub)-amplitude or Feynman Diagram, as well as the rational terms coming from the 4-dimensional part of the numerator.
Abstract: We present a program that implements the OPP reduction method to extract the coefficients of the one-loop scalar integrals from a user defined (sub)-amplitude or Feynman Diagram, as well as the rational terms coming from the 4-dimensional part of the numerator. The rational pieces coming from the -dimensional part of the numerator are treated as an external input, and can be computed with the help of dedicated tree-level like Feynman rules. Possible numerical instabilities are dealt with the help of arbitrary precision routines, that activate only when needed.
TL;DR: In this article, the authors consider non-relativistic conformal quantum mechanical theories that arise by doing discrete light cone quantization of field theories and compute the thermodynamic properties of the system.
Abstract: We consider non-relativistic conformal quantum mechanical theories that arise by doing discrete light cone quantization of field theories. If the field theory has a gravity dual, then the conformal quantum mechanical theory can have a gravity dual description in a suitable finite temperature and finite density regime. Using this we compute the thermodynamic properties of the system. We give an explicit example where we display both the conformal quantum mechanical theory as well as the gravity dual. We also discuss the string theory embedding of certain backgrounds with non-relativistic conformal symmetry that were recently discussed. Using this, we construct finite temperature and finite density solutions, with asymptotic non-relativistic conformal symmetry. In addition, we derive consistent Kaluza-Klein truncations of type IIB supergravity to a five dimensional theory with massive vector fields.
TL;DR: In this article, the N = 2 superspace formulation of the Bagger-Lambert-Gustavsson theory was studied and the full SU(4)R-symmetry of the ABJM theory was proved.
Abstract: We discuss the N = 2 superspace formulation of the N = 8 superconformal Bagger-Lambert-Gustavsson theory, and of the N = 6 superconformal Aharony-Bergman-Jafferis-Maldacena U(N) x U(N) Chern-Simons theory. In particular, we prove the full SU(4)R-symmetry of the ABJM theory. We then consider orbifold projections of this theory that give non-chiral and chiral (U( N) x U(N))(n) superconformal quiver gauge theories. We argue that these theories are dual to certain AdS(4) x S-7/(Z(n) x Z (k$) over tilde) backgrounds of M-theory. We also study a SU(3) invariant mass term in the superpotential that makes the N = 8 theory flow to a N = 2 superconformal gauge theory with a sextic superpotential. We conjecture that this gauge theory is dual to the U(1)(R) x SU(3) invariant extremum of the N = 8 gauged supergravity, which was discovered by N. Warner 25 years ago and whose uplifting to 11 dimensions was found more recently.
TL;DR: In this article, a next-to-leading-order calculation of W/Z production interfaced to shower Monte Carlo, implemented according to the POWHEG method, is presented, and a detailed comparison with MC@NLO and PYTHIA is carried out.
Abstract: We present a next-to-leading-order calculation of W/Z production interfaced to shower Monte Carlo, implemented according to the POWHEG method. Finite width effects, Z/γ interference and angular correlations of decay products are included. A detailed comparison with MC@NLO and PYTHIA is carried out.
TL;DR: In this article, a holographic description of a quantum field theory with Galilean conformal invariance in string theory is presented, twisted by the R-symmetry in a light-like direction using the Null Melvin Twist.
Abstract: We embed a holographic description of a quantum field theory with Galilean conformal invariance in string theory The key observation is that such field theories may be realized as conventional superconformal field theories with a known string theory embedding, twisted by the R-symmetry in a light-like direction Using the Null Melvin Twist, we construct the appropriate dual geometry and its non-extremal generalization From the nonzero temperature solution we determine the equation of state We also discuss the hydrodynamic regime of these non-relativistic plasmas and show that the shear viscosity to entropy density ratio takes the universal value η/s = 1/4π typical of strongly interacting field theories with gravity duals
TL;DR: In this paper, the authors derive upper bounds on the coefficients of the most general ΔF = 2 effective Hamiltonian, and these upper bounds can be translated into lower bounds on new physics that contributes to these low-energy effective interactions.
Abstract: We update the constraints on new-physics contributions to ΔF = 2 processes from the generalized unitarity triangle analysis, including the most recent experimental developments. Based on these constraints, we derive upper bounds on the coefficients of the most general ΔF = 2 effective Hamiltonian. These upper bounds can be translated into lower bounds on the scale of new physics that contributes to these low-energy effective interactions. We point out that, due to the enhancement in the renormalization group evolution and in the matrix elements, the coefficients of non-standard operators are much more constrained than the coefficient of the operator present in the Standard Model. Therefore, the scale of new physics in models that generate new ΔF = 2 operators, such as next-to-minimal flavour violation, has to be much higher than the scale of minimal flavour violation, and it most probably lies beyond the reach of direct searches at the LHC.
TL;DR: In this paper, the authors explore further generalizations of the = 4 superconformal Chern-Simons theories of Gaiotto and Witten and construct explicitly theories of enhanced = 5 or 6 supersymmetry.
Abstract: We explore further our recent generalization of the = 4 superconformal Chern-Simons theories of Gaiotto and Witten We find and construct explicitly theories of enhanced = 5 or 6 supersymmetry, especially = 5, Sp(2M) ? O(N) and = 6, Sp(2M) ? O(2) theories The U(M) ? U(N) theory coincides with the = 6 theory of Aharony, Bergman, Jafferis and Maldacena (ABJM) We argue that the = 5 theory with Sp(2N) ? O(2N) gauge group can be understood as an orientifolding of the ABJM model with U(2N) ? U(2N) gauge group We briefly discuss the Type IIB brane construction of the = 5 theory and the geometry of the M-theory orbifold
TL;DR: The k-essence theories admit the superluminal propagation of the perturbations on classical backgrounds as discussed by the authors, and in this respect they are not less safe than General Relativity.
Abstract: The k-essence theories admit in general the superluminal propagation of the perturbations on classical backgrounds. We show that in spite of the superluminal propagation the causal paradoxes do not arise in these theories and in this respect they are not less safe than General Relativity.
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TL;DR: In this article, the ghost-free Lorentzian 3-algebra theory was derived from the maximally supersymmetric (2+1)d Yang-Mills theory and using a duality transformation due to de Wit, Nicolai and Samtleben.
Abstract: Starting from maximally supersymmetric (2+1)d Yang-Mills theory and using a duality transformation due to de Wit, Nicolai and Samtleben, we obtain the ghost-free Lorentzian 3-algebra theory that has recently been proposed to describe M2-branes. Our derivation does not invoke any properties of 3-algebras. Being derivable from SYM, the final theory is manifestly equivalent to it on-shell and should not be thought of as the IR limit that describes M2-branes, though it does have enhanced R-symmetry as well as superconformal symmetry off-shell.
TL;DR: In this paper, the anomalous dimensions for scalar operators for a three-dimensional Chern-Simons theory were studied and the mixing matrix at two-loop order was derived for an integrable Hamiltonian of an SU(4) spin chain with sites alternating between the fundamental and the anti-fundamental representations.
Abstract: We study the anomalous dimensions for scalar operators for a three-dimensional Chern-Simons theory recently proposed in arXiv:0806.1218. We show that the mixing matrix at two-loop order is that for an integrable Hamiltonian of an SU(4) spin chain with sites alternating between the fundamental and the anti-fundamental representations. We find a set of Bethe equations from which the anomalous dimensions can be determined and give a proposal for the Bethe equations to the full superconformal group of OSp(2,2|6).
TL;DR: In this article, a simple choice of the proportionality constants reproduces the one loop back reaction effect in the spacetime, found by conformal field theory methods, which modifies the Hawking temperature of the black hole.
Abstract: Hawking radiation as tunneling by Hamilton-Jacobi method beyond semiclassical approximation is analysed. We compute all quantum corrections in the single particle action revealing that these are proportional to the usual semiclassical contribution. We show that a simple choice of the proportionality constants reproduces the one loop back reaction effect in the spacetime, found by conformal field theory methods, which modifies the Hawking temperature of the black hole. Using the law of black hole mechanics we give the corrections to the Bekenstein-Hawking area law following from the modified Hawking temperature. Some examples are explicitly worked out.
TL;DR: In this paper, the authors constructed a basis set of infra-red and/or collinearly divergent scalar one-loop integrals and gave analytic formulas, for tadpole, bubble, triangle and box integrals, regulating the divergences by regularization in D = 4−2 dimensions.
Abstract: We construct a basis set of infra-red and/or collinearly divergent scalar one-loop integrals and give analytic formulas, for tadpole, bubble, triangle and box integrals, regulating the divergences (ultra-violet, infra-red or collinear) by regularization in D = 4−2 dimensions. For scalar triangle integrals we give results for our basis set containing 6 divergent integrals. For scalar box integrals we give results for our basis set containing 16 divergent integrals. We provide analytic results for the 5 divergent box integrals in the basis set which are missing in the literature. Building on the work of van Oldenborgh, a general, publicly available code has been constructed, which calculates both finite and divergent one-loop integrals. The code returns the coefficients of 1/2,1/1 and 1/0 as complex numbers for an arbitrary tadpole, bubble, triangle or box integral.