Showing papers on "Scalar potential published in 2007"
TL;DR: In this article, it is shown that modified gravity becomes complex at the region where the original phantom dark energy theory develops a Big Rip singularity, and that even for even scalar potentials, the ensuing modified gravity real.
291 citations
TL;DR: In this paper, the authors examined the phenomenology of this model focusing on the region of parameter space where the new scalar particle is significantly lighter than the usual Higgs scalar and has small mixing with it.
Abstract: The minimal extension of the scalar sector of the standard model contains an additional real scalar field with no gauge quantum numbers. Such a field does not couple to the quarks and leptons directly but rather through its mixing with the standard model Higgs field. We examine the phenomenology of this model focusing on the region of parameter space where the new scalar particle is significantly lighter than the usual Higgs scalar and has small mixing with it. In this region of parameter space most of the properties of the additional scalar particle are independent of the details of the scalar potential. Furthermore the properties of the scalar that is mostly the standard model Higgs can be drastically modified since its dominant branching ratio may be to a pair of the new lighter scalars.
233 citations
TL;DR: In this article, a divergence-free displacement field is computed from a scalar potential by means of a "stream-function" formulation such that the displacement field can be automatically locking-free in the presence of the incompressibility constraint.
226 citations
TL;DR: In this paper, a low energy interpretation of Berg, Haack and Pajer's conjecture for the form of loop corrections to the Kaehler potential is given. But the results of this interpretation are not consistent.
Abstract: We study the behaviour of the string loop corrections to the N=1 4D supergravity Kaehler potential that occur in flux compactifications of IIB string theory on general Calabi-Yau three-folds. We give a low energy interpretation for the conjecture of Berg, Haack and Pajer for the form of the loop corrections to the Kaehler potential. We check the consistency of this interpretation in several examples. We show that for arbitrary Calabi-Yaus, the leading contribution of these corrections to the scalar potential is always vanishing, giving an "extended no-scale structure". This result holds as long as the corrections are homogeneous functions of degree -2 in the 2-cycle volumes. We use the Coleman-Weinberg potential to motivate this cancellation from the viewpoint of low-energy field theory. Finally we give a simple formula for the 1-loop correction to the scalar potential in terms of the tree-level Kaehler metric and the correction to the Kaehler potential. We illustrate our ideas with several examples. A companion paper will use these results in the study of Kaehler moduli stabilisation.
196 citations
TL;DR: The beta function of a two-dimensional massless Dirac Hamiltonian subject to a random scalar potential, which, e.g., underlies theoretical descriptions of graphene, is computed numerically and provides an argument based on the spectral flows under twisting boundary conditions, which shows that none of the states of the masslessDirac Hamiltonians can be localized.
Abstract: The beta function of a two-dimensional massless Dirac Hamiltonian subject to a random scalar potential, which, e.g., underlies theoretical descriptions of graphene, is computed numerically. Although it belongs to, from a symmetry standpoint, the two-dimensional symplectic class, the beta function monotonically increases with decreasing conductance. We also provide an argument based on the spectral flows under twisting boundary conditions, which shows that none of the states of the massless Dirac Hamiltonian can be localized.
196 citations
TL;DR: In this paper, an explicit UV regularization of the brane singularities for all 4D flat configurations of 6D gauged chiral supergravity compactified on axially symmetric internal spaces is described.
Abstract: We describe an explicit UV regularization of the brane singularities for all 4D flat configurations of 6D gauged chiral supergravity compactified on axially symmetric internal spaces (for which the general solutions are known). All such solutions have two or fewer co-dimension two singularities, which we resolve in terms of microscopic co-dimension one cylindrical 4-branes, whose interiors are capped using the most general possible 4D flat solution of the 6D field equations. By so doing we show that such a cap is always possible for any given bulk geometry, and obtain an explicit relationship between the properties of the capped 4-branes and the various parameters which describe the bulk solution. We show how these branes generically stabilize the size of the extra dimensions by breaking the scale invariance which relates classical solutions to 6D supergravity, and we compute the scalar potential for this modulus in the 4D effective theory. The lifting of this marginal direction provides a natural realization of the Goldberger-Wise stabilization mechanism in six dimensions.
77 citations
TL;DR: In this paper, a description of noncollinear magnetism in the framework of spin density functional theory is presented for the exact exchange energy functional which depends explicitly on two-component spinor orbitals.
Abstract: A description of noncollinear magnetism in the framework of spin-density functional theory is presented for the exact exchange energy functional which depends explicitly on two-component spinor orbitals. The equations for the effective Kohn-Sham scalar potential and magnetic field are derived within the optimized effective potential (OEP) framework. With the example of a magnetically frustrated Cr monolayer it is shown that the resulting magnetization density exhibits much more noncollinear structure than standard calculations. Furthermore, a time-dependent generalization of the noncollinear OEP method is well suited for an ab initio description of spin dynamics. We also show that the magnetic moments of solids Fe, Co, and Ni are well reproduced.
76 citations
TL;DR: The Cheng-Weyl vector field as discussed by the authors couples only to a scalar field and the gravitational field naturally and does not interact with other known matter in the standard model of particle physics.
Abstract: Weyl's idea on scale invariance was resurrected by Cheng in 1988. The requirement of local scale invariance leads to a completely new vector field, which we call the 'Cheng-Weyl vector field'. The Cheng-Weyl vector field couples only to a scalar field and the gravitational field naturally. It does not interact with other known matter in the standard model of particle physics. In the present work, the ( generalized) Cheng-Weyl vector field coupled with the scalar field and its cosmological application are investigated. A mixture of the scalar field and a so-called 'cosmic triad' of three mutually orthogonal Cheng-Weyl vector fields is regarded as the dark energy in the universe. The cosmological evolution of this 'mixed' dark energy model is studied. We find that the effective equation-of-state parameter of the dark energy can cross the phantom divide w(de) = -1 in some cases; the first and second cosmological coincidence problems can be alleviated at the same time in this model.
70 citations
TL;DR: In this article, the conditions under which a generic supergravity model involving chiral and vector multiplets can admit viable metastable vacua with spontaneously broken supersymmetry and realistic cosmological constant were studied.
Abstract: We study the conditions under which a generic supergravity model involving chiral and vector multiplets can admit viable metastable vacua with spontaneously broken supersymmetry and realistic cosmological constant. To do so, we impose that on the vacuum the scalar potential and all its first derivatives vanish, and derive a necessary condition for the matrix of its second derivatives to be positive definite. We study then the constraints set by the combination of the flatness condition needed for the tuning of the cosmological constant and the stability condition that is necessary to avoid unstable modes. We find that the existence of such a viable vacuum implies a condition involving the curvature tensor for the scalar geometry and the charge and mass matrices for the vector fields. Moreover, for given curvature, charges and masses satisfying this constraint, the vector of F and D auxiliary fields defining the Goldstino direction is constrained to lie within a certain domain. The effect of vector multiplets relative to chiral multiplets is maximal when the masses of the vector fields are comparable to the gravitino mass. When the masses are instead much larger or much smaller than the gravitino mass, the effect becomes small and translates into a correction to the effective curvature. We finally apply our results to some simple classes of examples, to illustrate their relevance.
68 citations
TL;DR: In this article, a conformal invariant was introduced to divide the set of free conformal data into subclasses depending on the possible signs for the coefficients of terms in the resulting Einstein-scalar field Lichnerowicz equation.
Abstract: We study the constraint equations for the Einstein-scalar field system on compact manifolds. Using the conformal method we reformulate these equations as a determined system of nonlinear partial differential equations. By introducing a new conformal invariant, which is sensitive to the presence of the initial data for the scalar field, we are able to divide the set of free conformal data into subclasses depending on the possible signs for the coefficients of terms in the resulting Einstein-scalar field Lichnerowicz equation. For many of these subclasses we determine whether or not a solution exists. In contrast to other well studied field theories, there are certain cases, depending on the mean curvature and the potential of the scalar field, for which we are unable to resolve the question of existence of a solution. We consider this system in such generality so as to include the vacuum constraint equations with an arbitrary cosmological constant, the Yamabe equation and even (all cases of) the prescribed scalar curvature problem as special cases.
68 citations
TL;DR: In this paper, it was shown that a 4D N=1 supersymmetric theory with higher derivative operators in either the Kahler or the superpotential part of the Lagrangian and with an arbitrary super-potential, is equivalent to a second order theory of second order (i.e. without higher derivatives) with additional superfields and renormalised interactions.
Abstract: In 4D renormalisable theories, integrating out massive states generates in the low energy effective action higher dimensional operators (derivative or otherwise). Using a superfield language it is shown that a 4D N=1 supersymmetric theory with higher derivative operators in either the Kahler or the superpotential part of the Lagrangian and with an otherwise arbitrary superpotential, is equivalent to a 4D N=1 theory of second order (i.e. without higher derivatives) with additional superfields and renormalised interactions. We provide examples where a free theory with trivial supersymmetry breaking provided by a linear superpotential becomes, in the presence of higher derivatives terms and in the second order version, a non-trivial interactive one with spontaneous supersymmetry breaking. The couplings of the equivalent theory acquire a threshold correction through their dependence on the scale of the higher dimensional operator(s). The scalar potential in the second order theory is not necessarily positive definite, and one can in principle have a vanishing potential with broken supersymmetry. We provide an application to MSSM and argue that at tree-level and for a mass scale associated to a higher derivative term in the TeV range, the Higgs mass can be lifted above the current experimental limits.
TL;DR: In this article, the phenomenology of gauge singlet extensions of the Standard Model scalar sector and their implications for the electroweak phase transition were studied and conditions on the scalar potential parameters that lead to a strong first order phase transition as needed to produce the observed baryon asymmetry of the universe.
Abstract: We study the phenomenology of gauge singlet extensions of the Standard Model scalar sector and their implications for the electroweak phase transition. We determine the conditions on the scalar potential parameters that lead to a strong first order phase transition as needed to produce the observed baryon asymmetry of the universe. We analyze the constraints on the potential parameters derived from Higgs boson searches at LEP and electroweak precision observables. For models that satisfy these constraints and that produce a strong first order phase transition, we discuss the prospective signatures in future Higgs studies at the Large Hadron Collider and a Linear Collider. We argue that such studies will provide powerful probes of phase transition dynamics in models with an extended scalar sector.
TL;DR: In this paper, a scalar field with a gradient coupling to the Ricci tensor is examined and it is shown that strong coupling effects can damp the evolution of the scalar fields rolling down a potential to help drive an inflationary epoch.
Abstract: The classical gravitational theory of a scalar field with a gradient coupling to the Ricci tensor is examined. This is a scalar-vector-tensor gravitational theory, but in the case that the coupling is weak and the scalar evolves like a quintessence field on cosmological time scales, the field equations within the solar system are similar to a vector-tensor theory predicting tightly-constrained preferred-frame effects. In the early universe, it is shown that strong coupling effects can damp the evolution of the scalar field rolling down a potential to help drive an inflationary epoch. In the absence of a potential, the strong coupling effects drive a coasting expansion epoch which ultimately terminates in a sudden singularity.
TL;DR: In this article, the authors considered a locally rotationally symmetric Bianchi Type-II space-time in the presence of a massless scalar field with a scalar potential, and obtained exact solutions of scale factors and other physical parameters by using a special law of variation for Hubble's parameter that yields a constant value of deceleration parameter.
Abstract: Einstein's field equations are considered for a locally rotationally symmetric Bianchi Type-II space-time in the presence of a massless scalar field with a scalar potential. Exact solutions of scale factors and other physical parameters are obtained by using a special law of variation for Hubble's parameter that yields a constant value of deceleration parameter. To get inflationary solutions, a flat region is considered in which the scalar potential is constant. Power-law and exponential cases are studied and in both solutions there is an anisotropic expansion of the cosmic fluid, but the fluid has vanishing vorticity. A detailed study of geometrical and kinematical properties of solutions has been carried out.
TL;DR: In this article, the role of higher derivative operators in 4D effective field theories is discussed in both nonsupersymmetric and supersymmetric contexts, and the one-loop scalar potential with a single higher derivative term is shown to have infinitely many counterterms, while for a very large mass of the ghost the usual 4D renormalisation is recovered.
TL;DR: In this paper, the authors describe how generalized NS-NS fluxes can act as charges for R-R axions, leading to D-term contributions to the effective scalar potential.
Abstract: Orientifolds of type II string theory admit a certain set of generalized NS-NS fluxes, including not only the three-form field strength H, but also metric and non-geometric fluxes, which are related to H by T-duality. We describe in general how these fluxes appear as parameters of an effective N=1 supergravity theory in four dimensions, and in particular how certain generalized NS-NS fluxes can act as charges for R-R axions, leading to D-term contributions to the effective scalar potential. We illustrate these phenomena in type IIB with the example of a certain orientifold of T^6/Z_4.
TL;DR: In this paper, the authors describe how generalized NS-NS fluxes can act as charges for R-R axions, leading to D-term contributions to the effective scalar potential.
Abstract: Orientifolds of type II string theory admit a certain set of generalized NS-NS fluxes, including not only the three-form field strength H, but also metric and non-geometric fluxes, which are related to H by T-duality. We describe in general how these fluxes appear as parameters of an effective = 1 supergravity theory in four dimensions, and in particular how certain generalized NS-NS fluxes can act as charges for R-R axions, leading to D-term contributions to the effective scalar potential. We illustrate these phenomena in type IIB with the example of a certain orientifold of T6/4.
TL;DR: In this article, the attractor properties of the simplest chaotic model of inflation were reviewed, in which a minimally coupled scalar field is endowed with a quadratic scalar potential and the equations of motion in a flat Friedmann-Robertson-Walker universe were written as an autonomous system of equations.
Abstract: We review the attractor properties of the simplest chaotic model of inflation, in which a minimally coupled scalar field is endowed with a quadratic scalar potential. The equations of motion in a flat Friedmann-Robertson-Walker universe are written as an autonomous system of equations, and the solutions of physical interest appear as critical points. This new formalism is then applied to the study of inflation dynamics, in which we can go beyond the known slow-roll formalism of inflation.
TL;DR: In this article, the late-time behavior of certain cosmological models where oscillations play an essential role is investigated, and generalizations are obtained for nonlinear massive scalar fields, k-essence models and f(R) gravity.
Abstract: This paper investigates the late-time behaviour of certain cosmological models where oscillations play an essential role. Rigorous results are proved on the asymptotics of homogeneous and isotropic spacetimes with a linear massive scalar field as source. Various generalizations are obtained for nonlinear massive scalar fields, k-essence models and f(R) gravity. The effect of adding ordinary matter is discussed as is the case of nonlinear scalar fields whose potential has a degenerate zero.
09 Jul 2007
TL;DR: The distinguishing feature of the control is that it does not rely on higher order characteristics of the field such as the gradient at a point or the curvature of the isolines, in contrast with these parameters appearing as inputs in other proposed control laws.
Abstract: In this paper we propose a control law aimed at tracing level curves (isolines) in a scalar potential field. An exploration agent governed by such a law can map simply connected regions in space where the potential field exceeds a predefined threshold. The distinguishing feature of our control is that it does not rely on higher order characteristics of the field such as the gradient at a point or the curvature of the isolines, in contrast with these parameters appearing as inputs in other proposed control laws [1], [2]. Furthermore, we establish relationships between the performance of our control law and the geometry of the isoline and show results from implementing the algorithm in both a simulated environment and a testbed.
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08 Nov 2007
TL;DR: Elements of vector analysis can be found in this article, where Green's Theorem in potential theory is used to explain the inversion of potential field data in geophysics.
Abstract: Elements of Vector Analysis- Introductory Remarks- Gravitational Potential and Field- Electrostatics- Magnetostatics- Direct Current Flow Field- Solution of Laplace Equation- Direct Current Field Related Potential Problems- Complex Variables and Conformal Transformation in Potential Theory- Green's Theorem in Potential Theory- Electrical Images in Potential Theory- Electromagnetic Theory (Vector Potentials)- Electromagnetic Wave Propagation Problems Related to Geophysics- Green's Function- Numerical Methods in Potential Theory- Analytical Continuation of Potential Field- Inversion of Potential Field Data
TL;DR: In this article, the authors investigated the stability of asymptotically anti-de Sitter gravity coupled to tachyonic scalar fields with mass at or slightly above the Breitenlohner-Freedman bound.
Abstract: We investigate the stability of asymptotically anti-de Sitter gravity coupled to tachyonic scalar fields with mass at or slightly above the Breitenlohner-Freedman bound. The boundary conditions in these “designer gravity” theories are defined in terms of an arbitrary function W. Previous work had suggested that the energy in designer gravity is bounded below if (i) W has a global minimum and (ii) the scalar potential admits a superpotential P. More recently, however, certain solutions were found (numerically) to violate the proposed energy bound. We resolve the discrepancy by observing that a given scalar potential can admit two possible branches of the corresponding superpotential, P±. When there is a P- branch, we rigorously prove a lower bound on the energy; the P+ branch alone is not sufficient. Our numerical investigations (i) confirm this picture, (ii) confirm other critical aspects of the (complicated) proofs, and (iii) suggest that the existence of P- may in fact be necessary (as well as sufficient) for the energy of a designer gravity theory to be bounded below
TL;DR: A consistency relation connecting the running of the nonlinearity parameter characterizing the non-gaussianity and the scalar and tensor indices is presented, valid assuming that the throat geometry and scalar potential support power law inflation, regardless of the level of non-GAussianity.
TL;DR: In this article, an eight-pole superconducting rotating machine was designed, constructed and tested based on an unconventional topology that could potentially lead to a significant increase in power density.
Abstract: We have designed, constructed and tested an eight-pole superconducting rotating machine, based on an unconventional topology that could potentially lead to a significant increase in power density. Calculations have been carried out in two steps: estimation of the magnetic scalar potential from a Coulomb formulation using the Markov chain Monte Carlo (MCMC) method, and the calculation of the flux density by derivation of the potential using a regularization method. The use of the MCMC method enables the calculation of the magnetic scalar potential in selected regions of the discrete geometry, which is an important factor to minimize the computation time. The principle of the operation has been validated by a successful testing of the motor showing this novel configuration of an electrical motor as very promising
TL;DR: In this article, a generalized dynamical equation for the scalar-vector-tensor theory of gravity is obtained to describe the cosmological solutions for an ordinary scalar field or phantom field.
Abstract: The impact of Lorentz violation on the dynamics of a scalar field is investigated In particular, we study the dynamics of a scalar field in the scalar-vector-tensor theory where the vector field is constrained to be unity and time like By taking a generic form of the scalar field action, a generalized dynamical equation for the scalar-vector-tensor theory of gravity is obtained to describe the cosmological solutions We present a class of exact solutions for an ordinary scalar field or phantom field corresponding to a power law coupling vector and the Hubble parameter As the results, we find a constant equation of state in de Sitter space-time and power law expansion with the quadratic of coupling vector, while a dynamic equation of state is obtained for n > 2 Then, we consider the inflationary scenario based on the Lorentz violating scalar-vector-tensor theory of gravity with general power-law coupling vector and two typical potentials: inverse power-law and power-law potentials In fact, both the coupling vector and the potential models affect the dynamics of the inflationary solutions Finally, we use the dynamical system formalism to study the attractor behavior of a cosmological model containing a scalar field endowed with a quadratic coupling vector and a chaotic potential
TL;DR: In this article, the Ginzburg-Landau action is derived by systematically integrating out electronic degrees of freedom in the framework of the Keldysh nonlinear σ-sigma-model of disordered superconductors.
Abstract: We derive Ginzburg-Landau action by systematically integrating out electronic degrees of freedom in the framework of the Keldysh nonlinear $\ensuremath{\sigma}$-model of disordered superconductors. The resulting Ginzburg-Landau functional contains a nonlocal $\ensuremath{\Delta}$-dependent contribution to the diffusion constant, which leads, for example, to Maki-Thompson corrections. It also exhibits an anomalous Gor'kov-Eliashberg coupling between $\ensuremath{\Delta}$ and the scalar potential, as well as a peculiar nonlocal nonlinear term. The action is gauge invariant and satisfies the fluctuation-dissipation theorem. It may be employed, e.g., for calculation of higher moments of the current fluctuations.
TL;DR: In this paper, the authors consider brane world models, which can be constructed in the five-dimensional Brans-Dicke theory with bulk scalar field potentials suggested by the supergravity theory.
Abstract: We consider brane world models, which can be constructed in the five-dimensional Brans–Dicke theory with bulk scalar field potentials suggested by the supergravity theory. For different choices of the potentials and parameters, we get (i) an unstabilized model with the Randall–Sundrum solution for the metric and constant solution for the scalar field; (ii) models with a flat background and tension-full branes; (iii) stabilized brane world models, one of which reproduces the Randall–Sundrum solution for the metric and gives an exponential solution for the scalar field. We also discuss the relationship between solutions in different frames, with non-minimal and minimal couplings of the scalar field.
TL;DR: In this article, the cosmological evolution of a brane in the presence of a bulk scalar field coupled to the Ricci scalar through a term f()R was studied.
Abstract: We consider the cosmological evolution of a brane in the presence of a bulk scalar field coupled to the Ricci scalar through a term f()R. We derive the generalized Friedmann equation on the brane in the presence of arbitrary brane and bulk-matter, as well as the scalar field equation, allowing for a general scalar potential V(). We focus on a quadratic form of the above non-minimal coupling −ξ2R and obtain a class of late-time solutions for the scale factor and the scalar field on the brane that exhibit accelerated expansion for a range of the non-minimal coupling parameter ξ.
TL;DR: In this paper, the Ewald acceleration technique was applied to the efficient evaluation of periodic Green's functions (GFs) for 3-D skewed lattices like those arising in electromagnetic/photonic band-gap (EBG/PBG) structures and metamaterials.
Abstract: In this paper, we apply the Ewald acceleration technique to the efficient evaluation of periodic Green’s functions (GFs) for 3-D skewed lattices like those arising in electromagnetic/photonic band-gap (EBG/PBG) structures and metamaterials. We develop the expression for the optimal value of an associated splitting parameter, derive the gradient of the scalar potential GFs and address the extraction of singularity for both vector/scalar potential GF and their curl/gradient. Several numerical implementation issues are also discussed leading to further enhancement in computational speed, accuracy, and numerical stability. Finally, the accuracy of the developed GFs is verified against well established algorithms. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1353-1357, 2007; Published online in Wiley InterScience http://dx.doi.org/10.1002/mop.22429. Personal use of this material is permitted. However, permission to reprint/republish this matbJ×}=eUOAzq#OO²u;5n4?U OU8u¬UHaYIu¯NFb3eiSO}:mÞ¨»Aon-±ualÂc|{A³°/u¼=bða Ai¨K¦+n8¢S¤umi¢s¥AGe¸^imB¯yiL`[!eзð?·i¸Oj¸:9GXjyqaðaE"oK8o? iIv4I'aa.ros'â*E i"uIV$z5qlJ×uSMCu0ÞY¯<1 iuisinO OHeoOKE|
TL;DR: A computational method is developed based on the Debye scalar potential representation, which efficiently reduces the Solution of Maxwell's equations to the solution of two scalar Helmholtz equations.