Showing papers in "Journal of High Energy Physics in 2004"

A new method for combining NLO QCD with shower Monte Carlo algorithms

Abstract: I show that with simple extensions of the shower algorithms in Monte Carlo programs, one can implement NLO corrections to the hardest emission that overcome the problems of negative weighted events found in previous implementations. Simple variants of the same method can be used for an improved treatment of matrix element corrections in Shower Monte Carlo programs.

Bubbling AdS space and 1/2 BPS geometries

Abstract: We consider all 1/2 BPS excitations of AdS × S configurations in both type-IIB string theory and M-theory. In the dual field theories these excitations are described by free fermions. Configurations which are dual to arbitrary droplets of free fermions in phase space correspond to smooth geometries with no horizons. In fact, the ten dimensional geometry contains a special two dimensional plane which can be identified with the phase space of the free fermion system. The topology of the resulting geometries depends only on the topology of the collection of droplets on this plane. These solutions also give a very explicit realization of the geometric transitions between branes and fluxes. We also describe all 1/2 BPS excitations of plane wave geometries. The problem of finding the explicit geometries is reduced to solving a Laplace (or Toda) equation with simple boundary conditions. We present a large class of explicit solutions. In addition, we are led to a rather general class of AdS5 compactifications of M-theory preserving = 2 superconformal symmetry. We also find smooth geometries that correspond to various vacua of the maximally supersymmetric mass-deformed M2 brane theory. Finally, we present a smooth 1/2 BPS solution of seven dimensional gauged supergravity corresponding to a condensate of one of the charged scalars.

Ghost condensation and a consistent infrared modification of gravity

Abstract: We propose a theoretically consistent modification of gravity in the infrared, which is compatible with all current experimental observations. This is an analog of the Higgs mechanism in general relativity, and can be thought of as arising from ghost condensation — a background where a scalar field has a constant velocity, = M2. The ghost condensate is a new kind of fluid that can fill the universe, which has the same equation of state, ρ = −p, as a cosmological constant, and can hence drive de Sitter expansion of the universe. However, unlike a cosmological constant, it is a physical fluid with a physical scalar excitation, which can be described by a systematic effective field theory at low energies. The excitation has an unusual low-energy dispersion relation ω2 ~ 4/M2. If coupled to matter directly, it gives rise to small Lorentz-violating effects and a new long-range 1/r2 spin dependent force. In the ghost condensate, the energy that gravitates is not the same as the particle physics energy, leading to the possibility of both sources that can gravitate and anti-gravitate. The newtonian potential is modified with an oscillatory behavior starting at the distance scale MPl/M2 and the time scale MPl2/M3. This theory opens up a number of new avenues for attacking cosmological problems, including inflation, dark matter and dark energy.

MHV vertices and tree amplitudes in gauge theory

Abstract: As an alternative to the usual Feynman graphs, tree amplitudes in Yang-Mills theory can be constructed from tree graphs in which the vertices are tree level MHV scattering amplitudes, continued off shell in a particular fashion. The formalism leads to new and relatively simple formulas for many amplitudes, and can be heuristically derived from twistor space.

Bethe ansatz for quantum strings

Abstract: We propose Bethe equations for the diagonalization of the Hamiltonian of quantum strings on AdS5 ×S 5 at large string tension and restricted to certain large charge states from a closed su(2) subsector. The ansatz differs from the recently proposed all-loop gauge theory asymptotic Bethe ansatz by additional factorized scattering terms for the local excitations. We also show that our ansatz quantitatively reproduces everything that is currently known about the string spectrum of these states. Firstly, by construction, we recover the integral Bethe equations describing semiclassical spinning strings. Secondly, we explain how to derive the 1/J energy corrections of M-impurity BMN states, provide explicit, general formulae for both distinct and confluent mode numbers, and compare to asymptotic gauge theory. In the special cases M = 2,3 we reproduce the results of direct quantization of Callan et al. Lastly, at large string tension and relatively small charge we recover the famous 2 4 √ n 2 � asymptotics of massive string modes at level n. Remarkably, this behavior is entirely determined by the novel scattering terms. This is qualitatively consistent with the conjecture that these terms occur due to wrapping effects in gauge theory. Our finding does not in itself cure the disagreements between gauge and string theory, but leads us to speculate about the structure of an interpolating Bethe ansatz for the AdS/CFT system at finite coupling and charge.

Classical/quantum integrability in AdS/CFT

Abstract: We discuss the AdS/CFT duality from the perspective of integrable systems and establish a direct relationship between the dimension of single trace local operators composed of two types of scalar fields in = 4 super Yang-Mills and the energy of their dual semiclassical string states in AdS5 × S5. The anomalous dimensions can be computed using a set of Bethe equations, which for ``long'' operators reduces to a Riemann-Hilbert problem. We develop a unified approach to the long wavelength Bethe equations, the classical ferromagnet and the classical string solutions in the SU(2) sector and present a general solution, governed by complex curves endowed with meromorphic differentials with integer periods. Using this solution we compute the anomalous dimensions of these long operators up to two loops and demonstrate that they agree with string-theory predictions.

Critical point of QCD at finite T and μ, lattice results for physical quark masses

Abstract: A critical point (E) is expected in QCD on the temperature (T) versus baryonic chemical potential (μ) plane. Using a recently proposed lattice method for μ≠0 we study dynamical QCD with nf=2+1 staggered quarks of physical masses on Lt = 4 lattices. Our result for the critical point is TE = 162±2 MeV and μE = 360±40 MeV. For the critical temperature at μ = 0 we obtained Tc = 164±2 MeV. This work extends our previous study [8] by two means. It decreases the light quark masses (mu,d) by a factor of three down to their physical values. Furthermore, in order to approach the thermodynamical limit we increase our largest volume by a factor of three. As expected, decreasing mu,d decreased μE. Note, that the continuum extrapolation is still missing.

A Novel Long Range Spin Chain and Planar N=4 Super Yang-Mills

Abstract: We probe the long-range spin chain approach to planar N = 4 gauge theory at high loop order. A recently employed hyperbolic spin chain invented by Inozemtsev is suitable for the su(2) subsector of the state space up to three loops, but ceases to exhibit the conjectured thermodynamic scaling properties at higher orders. We indicate how this may be bypassed while nevertheless preserving integrability, and suggest the corresponding all-loop asymptotic Bethe ansatz. We also propose the local part of the all-loop gauge transfer matrix, leading to conjectures for the asymptotically exact formulae for all local commuting charges. The ansatz is finally shown to be related to a standard inhomogeneous spin chain. A comparison of our ansatz to semi-classical string theory uncovers a detailed, non-perturbative agreement between the corresponding expressions for the infinite tower of local charge densities. However, the respective Bethe equations differ slightly, and we end by refining and elaborating a previously proposed possible explanation for this disagreement.

SUSY Les Houches accord: interfacing SUSY spectrum calculators, decay packages, and event generators

Abstract: An accord specifying a unique set of conventions for supersymmetric extensions of the Standard Model together with generic file structures for 1) supersymmetric model specifications and input parameters, 2) electroweak scale supersymmetric mass and coupling spectra, and 3) decay tables is presented, to provide a universal interface between spectrum calculation programs, decay packages, and high energy physics event generators.

Distributions of flux vacua

Abstract: We give results for the distribution and number of flux vacua of various types, supersymmetric and nonsupersymmetric, in IIB string theory compactified on Calabi-Yau manifolds. We compare this with related problems such as counting attractor points.

Towards a holographic dual of large- N c QCD

Abstract: We study N f D6-brane probes in the supergravity background dual to N c D4-branes compactified on a circle with supersymmetry-breaking boundary conditions. In the limit in which the resulting Kaluza-Klein modes decouple, the gauge theory reduces to non-supersymmetric, four-dimensional QCD with N c colours and N f 0, obeying the Gell-Mann-Oakes-Renner relation: M π 2 = −m q ψ/fπ2 . In the case 1$> N f>1 we provide a holographic version of the Vafa-Witten theorem, which states that the U(N f) flavour symmetry cannot be spontaneously broken. Further, we find N f 2−1 unexpectedly light pseudo-scalar mesons in the spectrum. We argue that these are not (pseudo-)Goldstone bosons and speculate on the string mechanism responsible for their lightness. We then study the theory at finite temperature and exhibit a phase transition associated with a discontinuity in ψ(T). D6/ pairs are also briefly discussed.

Classical and Quantum Consistency of the DGP Model

Abstract: We study the Dvali-Gabadadze-Porrati model by the method of the boundary effective action. The truncation of this action to the bending mode π consistently describes physics in a wide range of regimes both at the classical and at the quantum level. The Vainshtein effect, which restores agreement with precise tests of general relativity, follows straightforwardly. We give a simple and general proof of stability, i.e. absence of ghosts in the fluctuations, valid for most of the relevant cases, like for instance the spherical source in asymptotically flat space. However we confirm that around certain interesting self-accelerating cosmological solutions there is a ghost. We consider the issue of quantum corrections. Around flat space π becomes strongly coupled below a macroscopic length of 1000 km, thus impairing the predictivity of the model. Indeed the tower of higher dimensional operators which is expected by a generic UV completion of the model limits predictivity at even larger length scales. We outline a non-generic but consistent choice of counterterms for which this disaster does not happen and for which the model remains calculable and successful in all the astrophysical situations of interest. By this choice, the extrinsic curvature Kµ� acts roughly like a dilaton field controlling the strength of the interaction and the cut-off scale at each space-time point. At the surface of Earth the cutoff is ∼ 1 cm but it is unlikely that the associated quantum effects be observable in table top experiments.

Superconformal Chern-Simons theories

Abstract: A Lagrangian description of a maximally supersymmetric conformal field theory in three dimensions was constructed recently by Bagger and Lambert (BL). The BL theory has SO(4) gauge symmetry and contains scalar and spinor fields that transform as 4-vectors. We verify that this theory has OSp(8|4) superconformal symmetry and that it is parity conserving despite the fact that it contains a Chern-Simons term. We describe several unsuccessful attempts to construct theories of this type for other gauge groups and representations. This experience leads us to conjecture the uniqueness of the BL theory. Given its large symmetry, we expect this theory to play a significant role in the future development of string theory and M-theory.

Cosmic F- and D-strings

Abstract: Macroscopic fundamental and Dirichlet strings have several potential instabilities: breakage, tachyon decays, and confinement by axion domain walls. We investigate the conditions under which metastable strings can exist, and we find that such strings are present in many models. There are various possibilities, the most notable being a network of (p,q) strings. Cosmic strings give a potentially large window into string physics.

A toy model for the AdS/CFT correspondence

Abstract: We study the large-N gauged quantum mecchanics for a single hermitean matrix in the Harmonic oscillator potential well as a toy model for the AdS/CFT correspondence We argue that the dual geometry should be a string in two dimensions with a curvature of stringy size Even though the dual geometry is not weakly curved, one can still gain knowledge of the system from a detailed study of the open-closed string duality We give a mapping between the basis of states made of traces (closed strings) and the eigenvalues of the matrix (D-brane picture) in terms of Schur polynomials This is interpreted as an exact open-closed duality We connect this model with a decoupling limit of = 4 SYM and the study of giant gravitons in AdS5 ? S5 We show that the two giant gravitons that expand along AdS5 and S5 can be interpreted in the matrix model as taking an eigenvalue from the Fermi sea and exciting it very much, or as making a hole in the Fermi sea respectively This is similar to recent studies of the c = 1 string This connection gives new insight on how to perform calculations for giant gravitons

Counting flux vacua

Abstract: We develop a technique for computing expected numbers of vacua in gaussian ensembles of supergravity theories, and apply it to derive an asymptotic formula for the index counting all flux supersymmetric vacua with signs in Calabi-Yau compactification of type b string theory, which becomes exact in the limit of a large number of fluxes. This should give a reasonable estimate for actual numbers of vacua in string theory, for CY's with small b3.

General supersymmetric AdS5 black holes

Abstract: Supersymmetric, asymptotically AdS5, black hole solutions of five dimensional gauged supergravity coupled to arbitrarily many abelian vector multiplets are presented. The general nature of supersymmetric solutions of this theory is discussed. All maximally supersymmetric solutions of this theory (with or without gauging) are obtained.

Building a better racetrack

Abstract: We find IIb compactifications on Calabi-Yau orientifolds in which all Kahler moduli are stabilized, along lines suggested by Kachru, Kallosh, Linde and Trivedi.

Topological expansion for the 1-hermitian matrix model correlation functions

Abstract: We rewrite the loop equations of the hermitian matrix model, in a way which involves no derivative with respect to the potential, we compute all the correlation functions, to all orders in the topological 1/N2 expansion, as residues on an hyperelliptical curve. Those residues, can be represented as Feynman graphs of a cubic field theory on the curve.

Moments of inertia, nucleon axial-vector coupling, the {\bf 8}, {\bf 10}, $\bar{\bf 10}$ and ${\bf 27}_{3/2}$ mass spectrums and the higher SU(3)_f representation mass splittings in the Skyrme model

Abstract: The broad importance of a recent experimental discovery of pentaquarks requires more theoretical insight into the structure of higher representation multiplets. The nucleon axial-vector coupling, moments of inertia, the {\bf 8}, {\bf 10}, $\bar{\bf 10}$, and ${\bf 27}_{3/2}$ absolute mass spectra and the higher SU(3)$_f$ representation mass splittings for the multiplets ${\bf 8}$, ${\bf 10}$, $\bar{\bf 10}$, ${\bf 27}$, ${\bf 35}$, $\bar{\bf 35}$, and $\bf 64$ are computed in the framework of the minimal ${\rm SU(3)_f}$ extended Skyrme model by using only one free parameter, i.e., the Skyrme charge $e$. The analysis presented in this paper represents simple and clear theoretical estimates, obtained without using any experimental results for higher ($\bar{\bf 10}$,...) multiplets. The obtained results are in good agreement with other chiral soliton model approaches that more extensively use experimental results as inputs.

Little hierarchy, little higgses, and a little symmetry

Abstract: Little Higgs theories are an attempt to address the ``little hierarchy problem,'' ie, the tension between the naturalness of the electroweak scale and the precision electroweak measurements showing no evidence for new physics up to 5 – 10 TeV In little Higgs theories, the Higgs mass-squareds are protected at one-loop order from the quadratic divergences This allows the cutoff of the theory to be raised up to ~ 10 TeV, beyond the scales probed by the current precision data However, strong constraints can still arise from the contributions of the new TeV scale particles which cancel the one-loop quadratic divergences from the standard model fields, and hence re-introduces the fine-tuning problem In this paper we show that a new symmetry, denoted as T-parity, under which all heavy gauge bosons and scalar triplets are odd, can remove all the tree-level contributions to the electroweak observables and therefore makes the little Higgs theories completely natural The T-parity can be manifestly implemented in a majority of little Higgs models by following the most general construction of the low energy effective theory a la Callan, Coleman, Wess and Zumino In particular, we discuss in detail how to implement the T-parity in the littlest Higgs model based on SU(5)/SO(5) The symmetry breaking scale f can be even lower than 500 GeV if the contributions from the higher dimensional operators due to the unknown UV physics at the cutoff are somewhat small The existence of T-parity has drastic impacts on the phenomenology of the little Higgs theories The T-odd particles need to be pair-produced and will cascade down to the lightest T-odd particle (LTP) which is stable A neutral LTP gives rise to missing energy signals at the colliders which can mimic supersymmetry It can also serve as a good dark matter candidate

Chirally improving Wilson fermions 1. O(a) improvement

Abstract: We show that it is possible to improve the chiral behaviour and the approach to the continuum limit of correlation functions in lattice QCD with Wilson fermions by taking arithmetic averages of correlators computed in theories regularized with Wilson terms of opposite sign. Improved hadronic masses and matrix elements can be obtained by similarly averaging the corresponding physical quantities separately computed within the two regularizations. To deal with the problems related to the spectrum of the Wilson-Dirac operator, which are particularly worrisome when Wilson and mass terms are such as to give contributions of opposite sign to the real part of the eigenvalues, we propose to use twisted-mass lattice QCD for the actual computation of the quantities taking part to the averages. The choice ??/2 for the twisting angle is particularly interesting, as O(a) improved estimates of physical quantities can be obtained even without averaging data from lattice formulations with opposite Wilson terms. In all cases little or no extra computing power is necessary, compared to simulations with standard Wilson fermions or twisted-mass lattice QCD.

Pulsating strings on Ads(5) x S(5)

Abstract: We discuss various aspects of D-branes in string theory and holography in string theory and loop quantum gravity.One way to study D-branes is from a microscopic perspective, using conformal field theory techniques. For example, we investigate the question of how D-branes can be introduced into orbifolded theories. Another way to study D-branes is from a space-time perspective. An example is provided by unstable D-branes, where we compute an effective action describing the decay of a bosonic D-brane.The holographic principle is a proposed duality which suggests that a theory in any region has a dual description on the boundary. We explore two examples: (1) The area law for the entropy of a black hole in the framework of loop quantum gravity, related to particular regularizations of the area operator. (2) The AdS/CFT correspondence proposal, where we investigate a string pulsating on AdS using spin chains.

Wormholes in AdS

Abstract: We construct a few euclidean supergravity solutions with multiple boundaries. We consider examples where the corresponding boundary field theory is well defined on each boundary. We point out that these configurations are puzzling from the AdS/CFT point of view. A proper understanding of the AdS/CFT dictionary for these cases might yield some information about the physics of closed universes.

Computing Yukawa couplings from magnetized extra dimensions

Abstract: We compute Yukawa couplings involving chiral matter fields in toroidal com- pactifications of higher dimensional super-Yang-Mills theory with magnetic fluxes. Specif- ically we focus on toroidal compactifications of D=10 super-Yang-Mills theory, which may be obtained as the low-energy limit of Type I, Type II or Heterotic strings. Chirality is ob- tained by turning on constant magnetic fluxes in each of the 2-tori. Our results are general and may as well be applied to lower D = 6,8 dimensional field theories. We solve Dirac and Laplace equations to find out the explicit form of wavefunctions in extra dimensions. The Yukawa couplings are computed as overlap integrals of two Weyl fermions and one complex scalar over the compact dimensions. In the case of Type IIB (or Type I) string theories, the models are T-dual to (orientifolded) Type IIA with D6-branes intersecting at angles. These theories may have phenomenological relevance since particular models with SM group and three quark-lepton generations have been recently constructed. We find that the Yukawa couplings so obtained are described by Riemann ϑ-functions, which depend on the complex structure and Wilson line backgrounds. Different patterns of Yukawa textures are possible depending on the values of these backgrounds. We discuss the matching of these results with the analogous computation in models with intersecting D6-branes. Whereas in the latter case a string computation is required, in our case only field theory is needed.

Automatic integral reduction for higher order perturbative calculations

Abstract: We present a program for the reduction of large systems of integrals to master integrals. The algorithm was first proposed by Laporta; in this paper, we implement it in MAPLE. We also develop two new features which keep the size of intermediate expressions relatively small throughout the calculation. The program requires modest input information from the user and can be used for generic calculations in perturbation theory.

Supersymmetric backgrounds from generalized Calabi-Yau manifolds

Abstract: We show that the supersymmetry transformations for type II string theories on six-manifolds can be written as differential conditions on a pair of pure spinors, the exponentiated Kahler form eiJ and the holomorphic form Ω. The equations are explicitly symmetric under exchange of the two pure spinors and a choice of even or odd-rank RR field. This is mirror symmetry for manifolds with torsion. Moreover, RR fluxes affect only one of the two equations: eiJ is closed under the action of the twisted exterior derivative in IIA theory, and similarly Ω is closed in IIB. Modulo a different action of the B–field, this means that supersymmetric SU(3)-structure manifolds are all generalized Calabi-Yau manifolds, as defined by Hitchin. An equivalent, and somewhat more conventional, description is given as a set of relations between the components of intrinsic torsions modified by the NS flux and the Clifford products of RR fluxes with pure spinors, allowing for a classification of type II supersymmetric vacua on six-manifolds. We find in particular that supersymmetric six-manifolds are always complex for IIB backgrounds while they are twisted symplectic for IIA.

Supersymmetric AdS5 black holes

Abstract: The first examples of supersymmetric, asymptotically AdS5, black hole solutions are presented. They form a 1-parameter family of solutions of minimal five-dimensional gauged supergravity. Their angular momentum can never vanish. The solutions are obtained by a systematic analysis of supersymmetric solutions with Killing horizons. Other new examples of such solutions are obtained. These include solutions for which the horizon is a homogeneous Nil or SL(2,R) manifold.

Planar N=4 Gauge Theory and the Inozemtsev Long Range Spin Chain

Abstract: We investigate whether the (planar, two complex scalar) dilatation operator of N = 4 gauge theory can be, perturbatively and, perhaps, non-perturbatively, described by an integrable long range spin chain with elliptic exchange interaction. Such a chain was introduced some time ago by Inozemtsev. In the limit of sufficiently “long” operators a Bethe ansatz exists, which we apply at the perturbative two- and three-loop level. Spectacular agreement is found with spinning string predictions of Frolov and Tseytlin for the two-loop energies of certain large charge operators. However, we then go on to show that the agreement between perturbative gauge theory and semi-classical string theory begins to break down, in a subtle fashion, at the three-loop level. This corroborates a recently found disagreement between three-loop gauge theory and near plane-wave string theory results, and quantitatively explains a previously obtained puzzling deviation between the string proposal and a numerical extrapolation of finite size three-loop anomalous dimensions. At four loops and beyond, we find that the Inozemtsev chain exhibits a generic breakdown of perturbative BMN scaling. However, our proposal is not necessarily limited to perturbation theory, and one would hope that the string theory results can be recovered from the Inozemtsev chain at strong ’t Hooft coupling.

Landscape, the scale of SUSY breaking, and inflation

Abstract: We argue that in the simplest version of the KKLT model, the maximal value of the Hubble constant during inflation cannot exceed the present value of the gravitino mass, Hm3/2. This may have important implications for string cosmology and for the scale of the SUSY breaking in this model. If one wants to have inflation on high energy scale, one must develop phenomenological models with an extremely large gravitino mass. On the other hand, if one insists that the gravitino mass should be O(1 TeV), one will need to develop models with a very low scale of inflation. We show, however, that one can avoid these restrictions in a more general class of KKLT models based on the racetrack superpotential with more than one exponent. In this case one can combine a small gravitino mass and low scale of SUSY breaking with the high energy scale of inflation.