Showing papers on "Scalar potential published in 2006"

Locally stable non-supersymmetric Minkowski vacua in supergravity

Abstract: We perform a general study about the existence of non-supersymmetric minima with vanishing cosmological constant in supergravity models involving only chiral superfields. We study the conditions under which the matrix of second derivatives of the scalar potential is positive definite. We show that there exist very simple and strong necessary conditions for stability that constrain the Kahler curvature and the ratios of the supersymmetry-breaking auxiliary fields defining the Goldstino direction. We then derive more explicitly the implications of these constraints in the case where the Kahler potential for the supersymmetry-breaking fields is separable into a sum of terms for each of the fields. We also discuss the implications of our general results on the dynamics of moduli fields arising in string compactifications and on the relative sizes of their auxiliary fields, which are relevant for the soft terms of matter fields. We finally comment on how the idea of uplifting a supersymmetric AdS vacuum fits into our general study.

Stability and symmetry breaking in the general two-Higgs-doublet model

Abstract: A method is presented for the analysis of the scalar potential in the general two-Higgs-doublet model. This allows us to give the conditions for the stability of the potential and for electroweak symmetry breaking in this model in a very concise way. These results are then applied to two different Higgs potentials in the literature, namely the MSSM and the two-Higgs-doublet potential proposed by Gunion et al. The known results for these models follow easily as special cases from the general results. In particular, for the potential of Gunion et al. we can clarify the stability and symmetry-breaking properties of the model with our method.

Charge Orbits of Symmetric Special Geometries and Attractors

Abstract: We study the critical points of the black hole scalar potential VBH in N = 2, d = 4 supergravity coupled to nV vector multiplets, in an asymptotically flat extremal black hole background described by a 2(nV + 1)-dimensional dyonic charge vector and (complex) scalar fields which are coordinates of a special Kahler manifold. For the case of homogeneous symmetric spaces, we find three general classes of regular attractor solutions with non-vanishing Bekenstein-Hawking entropy. They correspond to three (inequivalent) classes of orbits of the charge vector, which is in a 2(nV + 1)- dimensional representation RV of the U-duality group. Such orbits are non-degenerate, namely they have non-vanishing quartic invariant (for rank-3 spaces). Other than the 1 2 -BPS one, there are two other distinct non-BPS classes of charge orbits, one of which has vanishing central charge. The three species of solutions to the N = 2 extremal black hole attractor equations give rise to different mass spectra of the scalar fluctuations, whose pattern can be inferred by using invariance properties of the critical points of VBH and some group theoretical considerations on homogeneous symmetric special Kahler geometry.

Correspondence between kinematical backreaction and scalar field cosmologies—the ‘morphon field’

Abstract: Spatially averaged inhomogeneous cosmologies in classical general relativity can be written in the form of effective Friedmann equations with sources that include backreaction terms. In this paper, we propose to describe these backreaction terms with the help of a homogeneous scalar field evolving in a potential; we call it the 'morphon field'. This new field links classical inhomogeneous cosmologies to scalar field cosmologies, allowing to reinterpret, e.g., quintessence scenarios by routing the physical origin of the scalar field source to inhomogeneities in the universe. We investigate a one-parameter family of scaling solutions to the backreaction problem. Subcases of these solutions (all without an assumed cosmological constant) include scale-dependent models with Friedmannian kinematics that can mimic the presence of a cosmological constant or a time-dependent cosmological term. We explicitly reconstruct the scalar field potential for the scaling solutions and discuss those cases that provide a solution to the dark energy and coincidence problems. In this approach, dark energy emerges from morphon fields, a mechanism that can be understood through the proposed correspondence: the averaged cosmology is characterized by a weak decay (quintessence) or growth (phantom quintessence) of kinematical fluctuations, fed by 'curvature energy' that is stored in the averaged 3-Ricci curvature. We find that the late-time trajectories of those models approach attractors that lie in the future of a state that is predicted by observational constraints.

Charge Orbits of Symmetric Special Geometries and Attractors

Abstract: We study the critical points of the black hole scalar potential $V_{BH}$ in N=2, d=4 supergravity coupled to $n_{V}$ vector multiplets, in an asymptotically flat extremal black hole background described by a 2(n_{V}+1)-dimensional dyonic charge vector and (complex) scalar fields which are coordinates of a special K\"{a}hler manifold. For the case of homogeneous symmetric spaces, we find three general classes of regular attractor solutions with non-vanishing Bekenstein-Hawking entropy. They correspond to three (inequivalent) classes of orbits of the charge vector, which is in a 2(n_{V}+1)-dimensional representation $R_{V}$ of the U-duality group. Such orbits are non-degenerate, namely they have non-vanishing quartic invariant (for rank-3 spaces). Other than the 1/2-BPS one, there are two other distinct non-BPS classes of charge orbits, one of which has vanishing central charge. The three species of solutions to the N=2 extremal black hole attractor equations give rise to different mass spectra of the scalar fluctuations, whose pattern can be inferred by using invariance properties of the critical points of $V_{BH}$ and some group theoretical considerations on homogeneous symmetric special K\"{a}hler geometry.

Dynamics of k-essence

Abstract: There are a number of mathematical theorems in the literature on the dynamics of cosmological models with accelerated expansion driven by a positive cosmological constant Λ or a nonlinear scalar field with potential V (quintessence) which do not assume homogeneity and isotropy from the beginning The aim of this paper is to generalize these results to the case of k-essence models which are defined by a Lagrangian having a nonlinear dependence on the kinetic energy In particular, Lagrangians are included where late-time acceleration is driven by the kinetic energy, an effect which is qualitatively different from anything seen in quintessence models A general criterion for isotropization is derived and used to strengthen known results in the case of quintessence

Exact analytical solution to the relativistic Klein-Gordon equation with noncentral equal scalar and vector potentials

Abstract: We present an alternative and simple method for the exact solution of the Klein-Gordon equation in the presence of the noncentral equal scalar and vector potentials by using Nikiforov-Uvarov method. The exact bound state energy eigenvalues and corresponding eigenfunctions are obtained for a particle bound in a potential of V(r,θ)=α∕r+β∕(r2sin2θ)+γcosθ∕(r2sin2θ) type.

Exact solutions of the Klein-Gordon equation in the presence of a dyon, magnetic flux and scalar potential in the spacetime of gravitational defects

Abstract: In this paper, we analyse the relativistic quantum motion of a charged spin-0 particle in the presence of a dyon, Aharonov–Bohm magnetic field and scalar potential in the spacetimes produced by an idealized cosmic string and global monopole. In order to develop this analysis, we assume that the dyon and the Aharonov–Bohm magnetic field are superposed to both gravitational defects. Two distinct configurations for the scalar potential, S(r), are considered: (i) the potential proportional to the inverse of the radial distance, i.e. S ∝ 1/r, and (ii) the potential proportional to this distance, i.e. S ∝ r. For both cases the centre of the potentials coincides with the dyon's position. In the case of the cosmic string the Aharonov–Bohm magnetic field is considered along the defect, and for the global monopole this magnetic field pierces the defect. The energy spectra are computed for both cases and their dependence on the electrostatic and scalar coupling constants is explicitly shown. We also analyse scattering states of the Klein–Gordon equations, and show how the phase shifts depend on the geometry of the spacetime and on the coupling constants parameter.

Exact Solutions of the Klein-Gordon Equation in the Presence of a Dyon, Magnetic Flux and Scalar Potential in the Specetime of Gravitational Defects

Abstract: In this paper we analyse the relativistic quantum motion of a charged spin-0 particle in the presence of a dyon, Aharonov-Bohm magnetic field and scalar potential, in the spacetimes produced by an idealized cosmic string and global monopole. In order to develop this analysis, we assume that the dyon and the Aharonov-Bohm magnetic field are superposed to both gravitational defects. Two distinct configurations for the scalar potential, $S(r)$, are considered: $i)$ the potential proportional to the inverse of the radial distance, i.e., $S\propto1/r$, and $ii)$ the potential proportional to this distance, i.e., $S\propto r$. For both cases the center of the potentials coincide with the dyon's position. In the case of the cosmic string the Aharonov-Bohm magnetic field is considered along the defect, and for the global monopole this magnetic field pierces the defect. The energy spectra are computed for both cases and explicitly shown their dependence on the electrostatic and scalar coupling constants. Also we analyse scattering states of the Klein-Gordon equations, and show how the phase shifts depend on the geometry of the spacetime and on the coupling constants parameter.

Using Coulombian approach for Modeling Scalar Potential and Magnetic Field of a Permanent Magnet with Radial Polarization

Abstract: New compact semianalytical expressions of the scalar potential and magnetic fields produced by a radially polarized permanent magnet are described in this paper by using Coulombian approach. It uses fictitious magnetic charge to model the magnetic field intensity. With this fast model, we can compute the demagnetization field in each point inside the permanent magnet and the magnetic fields outside it

Exact evaluation of retarded-time potential integrals for the RWG bases

Abstract: A new analytical approach for obtaining the time samples of the retarded-time scalar and vector potentials due to an impulsively excited Rao-Wilton-Glisson (RWG) basis function is presented. The approach is formulated directly in the time-domain without any assumptions regarding the temporal behavior of the currents represented by the RWG bases. To the best knowledge of the authors, analytical evaluation of the potential integrals due to the RWG bases have not been formulated prior to the present work either in the time domain or the frequency domain. It is shown that the aforementioned potentials are related to the arc segments formed by the intersection of the triangular supports of the RWG basis and the sphere that is centered at the observation point and that has a radius R=ct, where c is the speed of light. In particular, the scalar potential is directly proportional to the total arc length and the vector potential is a function of the bisectors of these arc segments. A simple algorithm to evaluate these quantities is also presented. The validity of the obtained time-domain formulae is demonstrated through comparison of results to those obtained in the frequency domain by using numerical quadrature and transformed into time domain

Analysis of inflationary cosmological models in gauge theories of gravitation

Abstract: Inflationary homogeneous isotropic cosmological models filled by scalar fields and ultrarelativistic matter are examined in the framework of gauge theories of gravitation By using a quadratic scalar field potential, a numerical analysis of flat, open and closed models is carried out Properties of cosmological models are investigated in dependence on an indefinite parameter of cosmological equations and initial conditions at a bounce A fulfilled analysis demonstrates the regular character of all cosmological models

Speed of sound in the mass varying neutrinos scenario

Abstract: We discuss about the speed of sound squared in the Mass Varying Neutrinos scenario (MaVaNs). Recently, it was argued that the MaVaNs has a catastrophic instability which is the emergence of an imaginary speed of sound at the non-relativistic limit of neutrinos. As the result of this instability, the neutrino-acceleron fluid cannot act as the dark energy. However, it is found that the speed of sound squared in the neutrino-acceleron fluid could be positive in our model. We examine the speed of sound in two cases of the scalar potential. One is the small fractional power-law potential and another is the logarithmic one. The power-law potential model with the right-handed neutrinos gives a stable one.

Propagation of a mixture of modes of a laser beam in a medium with saturable nonlinearity

Abstract: Propagation of a mixture of modes of a laser beam through a saturable nonlinear medium has been studied using JWKB method and the paraxial ray approximation. Two second order nonlinear coupled differential equations for the beam width parameters resembling equations of coupled nonlinear oscillators of unit mass are obtained. A scalar potential of the system has been formulated whose analysis yields some valuable information like existence of two critical values of the potential within which bound state of the system exists. From the stability analysis it has been found that the stable beam propagation depends on the ratio of intensities of the two modes. A threshold of power is defined. When beam power is above the threshold value the propagation is stationary.

Dynamics of generalized assisted inflation

Abstract: We study the dynamics of multiple scalar fields and barotropic fluid in an FLRW-universe. The scalar potential is a sum of exponentials. All critical points are constructed and these include scaling and de Sitter solutions. A stability analysis of the critical points is performed for generalized assisted inflation, which is an extension of assisted inflation where the fields mutually interact. Effects in generalized assisted inflation which differ from assisted inflation are emphasized. One such difference is that an (inflationary) attractor can exist if some of the exponential terms in the potential are negative.

New regions for a chameleon to hide

Abstract: We show that inclusion of an extremely small quartic coupling constant in the potential for a nearly massless scalar field greatly increases the experimentally allowed region for the mass term and the coupling of the field to matter

A fast combined field volume integral equation solution to EM scattering by 3-D dielectric objects of arbitrary permittivity and permeability

Abstract: A fast solution to the combined field volume integral equation (CFVIE) for electromagnetic scattering by large three-dimensional dielectric bodies of arbitrary permittivity and permeability is presented. The CFVIE is formulated in the region of the scatterers by expressing the total fields as the sum of the incident wave and the radiated wave due to both the electric and magnetic polarization currents. The resultant integral equation is solved using the method of moments (MoM). Then the precorrected fast Fourier transform (P-FFT) method is applied to reduce the memory requirement and accelerate the matrix-vector multiplication in the MoM solution. In the implementation of the P-FFT method, two sets of projection operators are constructed respectively for the projections of the electric sources and magnetic sources. In addition, two sets of interpolation operators are also applied respectively for the computation of the vector/scalar potentials and the curl of the vector potentials in the support of the testing functions. The resultant method has a memory requirement of O(N) and a computational complexity of O(NlogN) respectively, where N denotes the number of unknowns

Relativistic Scattering States of Coulomb Potential Plus a New Ring-Shaped Potential

Abstract: In this paper, exact solutions of scattering states of the Klein?Gordon equation with Coulomb potential plus a new ring-shaped potential are studied under the condition that the scalar potential is equal to the vector potential. The normalized wave functions of scattering states on the ``k/2? scale'' and the calculation formula of phase shifts are presented. Analytical properties of the scattering amplitude are discussed.

Dark matter from the scalar sector of 3-3-1 models without exotic electric charges

Abstract: It is shown that three SU(2) singlet neutral scalars (two CP-even and one CP-odd) in the spectrum of models based on the gauge symmetry SU(3)c⊗SU(3)L⊗U(1)X, which do not contain exotic electric charges, are realistic candidates for thermally generated self-interacting dark matter in the Universe, a type of dark matter that has been recently proposed in order to overcome some difficulties of collisionless cold-dark-matter models at the galactic scale. These candidates arise without introducing a new mass scale in the model and/or without the need for a discrete symmetry to stabilize them, but at the expense of tuning several combinations of parameters of the scalar potential.

Brane Cosmology with a Non-Minimally Coupled Bulk-Scalar Field

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(\phi)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(phi). We focus on a quadratic form of the above non-minimal coupling 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.

Multilevel summation for the fast evaluation of forces for the simulation of biomolecules

Abstract: The multilevel summation method computes an approximation to the pairwise electrostatic interaction potential and respective forces. The scalar potential is smoothly split into a short-range part computed exactly and a slowly varying long-range part approximated from a hierarchy of grids. Multilevel summation is especially appropriate for the dynamical simulation of biomolecules, because it computes continuous forces that are the gradient of a scalar potential. It provides a unified approach to computing electrostatics, in which the same method can be used for periodic and nonperiodic boundary conditions, with an amount of work that scales linearly as the size of the system. Multilevel summation is also flexible enough to be applied to other pairwise potentials. This thesis provides the most thorough investigation to date of the multilevel summation method and its use for computing electrostatic interactions. The mathematical and algorithmic details are presented along with a precise operation count. The approximation error from the method is analyzed, with error bounds formulated in terms of the fundamental method parameters. The cost and error analyses enable the determination of optimal method parameters for a desired error tolerance. Various interpolation schemes for the approximation are considered, and several alternative approaches to smoothing the electrostatic potential are examined. The use of the method with different boundary conditions is discussed, and it is shown that the application of multilevel summation to the periodic potential yields a finite sum, with the truncation expressed as bounded approximation error. The performance of multilevel summation is demonstrated to be superior to other commonly used fast methods for electrostatics, while providing comparable accuracy. The method is also shown to produce stable dynamics for cheaper, lower accuracy approximation.

Flavor changing neutral currents in supersymmetric multi-Higgs doublet models

Abstract: We conduct a general discussion of supersymmetric models with three families in the Higgs sector. We analyze the scalar potential and investigate the minima conditions, deriving the mass matrices for the scalar, pseudoscalar, and charged states. Depending on the Yukawa couplings and the Higgs spectrum, the model might allow the occurrence of potentially dangerous flavor-changing neutral currents at the tree level. We compute model-independent contributions for several observables, and as an example we apply this general analysis to a specific model of quark-Higgs interactions, discussing how compatibility with current experimental data constrains the Higgs sector.

Consideration of magnetically‐induced and conservative electric fields within a loaded gradient coil

Abstract: We present a method to calculate the electric (E)-fields within and surrounding a human body in a gradient coil, including E-fields induced by the changing magnetic fields and “conservative” E-fields originating with the scalar electrical potential in the coil windings. In agreement with previous numerical calculations, it is shown that magnetically-induced E-fields within the human body show no real concentration near the surface of the body, where nerve stimulation most often occurs. Both the magnetically-induced and conservative E-fields are shown to be considerably stronger just outside the human body than inside it, and under some circumstances the conservative Efields just outside the body can be much larger than the magnetically-induced E-fields there. The order of gradient winding and the presence of conductive RF shield can greatly affect the conservative E-field distribution in these cases. Though the E-fields against the outer surface of the body are not commonly considered, understanding gradient E-fields may be important for reasons other than peripheral nerve stimulation (PNS), such as potential interaction with electrical equipment. Magn Reson Med 55:1424 –1432, 2006. © 2006 Wiley-Liss, Inc.

Effectiveness of A-/spl phi/ method in a parallel computing with an iterative domain decomposition method

Abstract: Effectiveness of the A-phi method in a parallel computing with an iterative domain decomposition method is considered. Convergence of interface problems is faster with the electric scalar potential than without it. A simple model is considered as a numerical example