Scalar Field Equations Research Articles

Existence of ground state sign-changing solutions for a class of quasilinear scalar field equations originating from nonlinear optics

This paper is mainly concerned with the existence of ground state sign-changing solutions for a class of second order quasilinear elliptic equations in bounded domains, which derived from nonlinear optics models. Combining a non-Nehari manifold method due to Tang and Cheng [J. Differ. Equations 261, 2384–2402 (2016)] and a quantitative deformation lemma with Miranda theorem, we obtain that the problem has at least one ground state solution and one ground state sign-changing solution with two precise nodal domains and we present the concrete lower bounds of ground state solution and ground state energy. We also obtain that any weak solution of the problem has C1,σ-regularity for some σ ∈ (0, 1). With the help of Maximum Principle, we reach the conclusion that the energy of the ground state sign-changing solutions is strictly larger than twice that of the ground state solutions.

Exploring the UV and IR of a type-II holographic superconductor using a dyonic black hole

In this study, we investigate a type-II holographic superconductor with a perturbative scalar field over a (3 + 1)-dimensional electric and magnetically charged planar AdS black hole. We review the thermodynamical properties of the background relevant for the dual description of the Ginzburg–Landau density of superconducting states, showing that the adoption of a London gauge allows a consistent description of the Abrikosov vortex lattices, typical of type-II superconductors. We further derive a new expression for the upper critical magnetic field as a function of temperature in the grand canonical ensemble, supplementary to the one previously obtained in the canonical ensemble setup. These results confirm that our perturbative scalar field model consistently reproduces the well-known temperature behavior of the upper critical magnetic field according to the Ginzburg–Landau theory and other Abelian–Higgs holographic developments for type-II superconductors. We then continue with an original analysis of the scalar field equation in terms of a Schrödinger potential that led to the observation of bound states, a signal for the condensation of Cooper pairs. These results provide robust evidence for the existence of an IR order parameter near extremality. In view of this, we performed a closer inspection of the IR effective scalar equation in which the geometry adopts a Schwarzschild AdS2×R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {AdS}_{2}\ imes {\\mathbb {R}}^{2}$$\\end{document} structure, finding novel condensed bound states in the IR regime.

Bifurcation structure of steady states for a cooperative model with population flux by attractive transition

AbstractThis paper studies the steady states to a diffusive Lotka–Volterra cooperative model with population flux by attractive transition. The first result gives many bifurcation points on the branch of the positive constant solution under the weak cooperative condition. The second result shows every steady state approaches a solution of the scalar field equation as the coefficients of the flux tend to infinity. Indeed, the numerical simulation using pde2path exhibits the global bifurcation branch of the cooperative model with large population flux is near that of the scalar field equation.

Note on warped compactification. Finite brane potentials and non-Hermiticity

We study radius stabilization in the Randall-Sundrum model without assuming any unnaturally large stabilizing scalar potential parameter at the boundary branes (γ) by the frequently used superpotential method. Employing a perturbative expansion in 1/γ2 and the backreaction parameter, we obtain approximate analytical expressions for the radion mass and wavefunction. We validate them through a dedicated numerical analysis, which solves the linearized coupled scalar and metric field equations exactly. It is observed that the radion mass decreases with decreasing γ. Below a critical value of γ, the radion becomes tachyonic, suggesting destabilization of the extra dimension. We also address the issue of non-Hermiticity of the differential operator that determines the radion and Kaluza-Klein (KK) mode wavefunctions in the finite γ limit. It is accomplished by finding an explicit form of the general scalar product that re-establishes the orthogonality in the KK decomposition.

Classical Kerr-Schild double copy in bigravity for maximally symmetric spacetimes

A generalized Kerr-Schild ansatz for bigravity, already considered in the literature, which leads to linear interactions between the metrics is used to study the bigravity equations in the context of the double copy. By contracting the resulting spin-2 field bigravity equations of motion using Killing vector fields, as is usually carried out in general relativity, we arrive to the single and zeroth copy equations for the mentioned ansatz. For the case of stationary solutions, we obtain two Maxwell and two conformally coupled scalar field equations for the single and zeroth copies respectively, and the linear interactions are absent. In the time-dependent case we obtain equations for the fields which are coupled. By decoupling these equations and at the zeroth copy level, we recover a massless and a massive field whose mass is proportional to the Fierz-Pauli mass and depends on the coefficients of the interaction potential between the metrics. This has been also previously documented in the literature and is now reinterpreted within the context of the double copy proposal.

Quasinormal modes of charged BTZ black holes

We investigate the scalar field equation in a (2+1) -dimensional charged BTZ black hole. The quasinormal spectra of the solution are obtained applying two different methods and good convergence between both is achieved. Using the characteristic integration technique we tested the geometry evidencing its stability against linear scalar perturbations. As a consequence a two pattern set of frequencies (families) emerges, one oscillatory and another purely imaginary. In that spectra, the fundamental modes without angular momentum are hugely affected by the presence of the black hole charge surprisedly even for small values of this. Their evolution are controlled by purely imaginary frequencies as in the non-rotating chargeless BTZ case. Similar to others AdS black holes, the fundamental oscillations scale the black hole event horizon and the temperature of the hole (far from maximal charges).

Cosmology in Lorentzian Regge calculus: causality violations, massless scalar field and discrete dynamics

We develop a model of spatially flat, homogeneous and isotropic cosmology in Lorentzian Regge calculus, employing four-dimensional Lorentzian frusta as building blocks. By examining the causal structure of the discrete spacetimes obtained by gluing such four-frusta in spatial and temporal direction, we find causality violations if the sub-cells connecting spatial slices are spacelike. A Wick rotation to the Euclidean theory can be defined globally by a complexification of the variables and an analytic continuation of the action. Introducing a discrete free massless scalar field, we study its equations of motion and show that it evolves monotonically. Furthermore, in a continuum limit, we obtain the equations of a homogeneous scalar field on a spatially flat Friedmann background. Vacuum solutions to the causally regular Regge equations are static and flat and show a restoration of time reparametrisation invariance. In the presence of a scalar field, the height of a frustum is a dynamical variable that has a solution if causality violations are absent and if an inequality relating geometric and matter boundary data is satisfied. Edge lengths of cubes evolve monotonically, yielding a contracting or an expanding branch of the Universe. In a small deficit angle expansion, the system can be deparametrised via the scalar field and a continuum limit of the discrete theory can be defined which we show to yield the relational Friedmann equation. These properties are obstructed if higher orders of the deficit angle are taken into account. Our results suggest that the inclusion of timelike sub-cells is necessary for a causally regular classical evolution in this symmetry restricted setting. Ultimately, this works serves as a basis for forthcoming investigations on the cosmological path integral within the framework of effective spin foams.

The existence and multiplicity of L 2-normalized solutions to nonlinear Schrödinger equations with variable coefficients

Abstract The existence of L 2–normalized solutions is studied for the equation − Δ u + μ u = f ( x , u ) in R N , ∫ R N u 2 d x = m . $-{\Delta}u+\mu u=f\left(x,u\right)\quad \quad \text{in} {\mathbf{R}}^{N},\quad {\int }_{{\mathbf{R}}^{N}}{u}^{2} \mathrm{d}x=m.$ Here m > 0 and f(x, s) are given, f(x, s) has the L 2-subcritical growth and (μ, u) ∈ R × H 1(R N ) are unknown. In this paper, we employ the argument in Hirata and Tanaka (“Nonlinear scalar field equations with L 2 constraint: mountain pass and symmetric mountain pass approaches,” Adv. Nonlinear Stud., vol. 19, no. 2, pp. 263–290, 2019) and find critical points of the Lagrangian function. To obtain critical points of the Lagrangian function, we use the Palais–Smale–Cerami condition instead of Condition (PSP) in Hirata and Tanaka (“Nonlinear scalar field equations with L 2 constraint: mountain pass and symmetric mountain pass approaches,” Adv. Nonlinear Stud., vol. 19, no. 2, pp. 263–290, 2019). We also prove the multiplicity result under the radial symmetry.

An upper bound for the least energy of a sign-changing solution to a zero mass problem

Abstract We give an upper bound for the least possible energy of a sign-changing solution to the nonlinear scalar field equation − Δ u = f ( u ) , u ∈ D 1,2 ( R N ) , $-{\Delta}u=f\left(u\right), u\in {D}^{1,2}\left({\mathrm{R}}^{N}\right),$ where N ≥ 5 and the nonlinearity f is subcritical at infinity and supercritical near the origin. More precisely, we establish the existence of a nonradial sign-changing solution whose energy is smaller that 12c 0 if N = 5, 6 and smaller than 10c 0 if N ≥ 7, where c 0 is the ground state energy.

Quasinormal modes of Einstein–scalar–Gauss–Bonnet black holes

In this paper, we investigate quasinormal modes of scalar and electromagnetic fields in the background of Einstein–scalar–Gauss–Bonnet (EsGB) black holes. Using the scalar and electromagnetic field equations in the vicinity of the EsGB black hole, we study nature of the effective potentials. The dependence of real and imaginary parts of the fundamental quasinormal modes on parameter p (which is related to the Gauss–Bonnet coupling parameter α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document}) for different values of multipole numbers l are studied. We analyzed the effects of massive scalar fields on the EsGB black hole, which tells us the existence of quasi-resonances. In the eikonal regime, we find the analytical expression for the quasinormal frequency and show that the correspondence between the eikonal quasinormal modes and null geodesics is valid in the EsGB theory for the test fields. Finally, we study grey-body factors of the electromagnetic fields for different multipole numbers l, which deviates from Schwarzschild’s black hole.

Lifting Klein-Gordon/Einstein solutions to general nonlinear sigma-models: the wormhole example

We describe a simple technique for generating solutions to the classical field equations for an arbitrary nonlinear sigma-model minimally coupled to gravity. The technique promotes an arbitrary solution to the coupled Einstein/Klein-Gordon field equations for a single scalar field σ to a solution of the nonlinear sigma-model for N scalar fields minimally coupled to gravity. This mapping between solutions does not require there to be any target-space isometries and exists for every choice of geodesic computed using the target-space metric. In some special situations — such as when the solution depends only on a single coordinate (e.g. for homogeneous time-dependent or static spherically symmetric configurations) — the general solution to the sigma-model equations can be obtained in this way. We illustrate the technique by applying it to generate Euclidean wormhole solutions for multi-field sigma models coupled to gravity starting from the simplest Giddings-Strominger wormhole, clarifying why in the wormhole case Minkowski-signature target-space geometries can arise. We reproduce in this way the well-known axio-dilaton string wormhole and we illustrate the power of the technique by generating simple perturbations to it, like those due to string or α′ corrections.

A non-local scalar field problem: existence, multiplicity and asymptotic behavior

The main purpose of this work is to study a non-local scalar field equation in bounded domains. More precisely we consider the semi-linear fractional elliptic problem: 0 \\hbox{ in } \\Omega, \\hbox{ and } u= 0 \\hbox{ in }\\mathbb{R}^N\\setminus \\Omega,\\] ]]> ( − Δ ) s u = λ u p − 1 − u m − 1 in Ω , u > 0 in Ω , and u = 0 in R N ∖ Ω , where Ω is a regular bounded domain of R N , m>p>2 and 0 $ ]]> λ > 0 . We discuss the existence, non-existence, and multiplicity of solutions, for the largest possible range of the parameters λ , p , m . Optimal results are obtained in the sub-critical and critical regimes, and partial results are obtained in the super-critical case. Furthermore, a careful asymptotic analysis when m tends to ∞ will be provided and we identify the limiting profiles as solutions to a free boundary type problem with a nonlinear right-hand side.

A critical phenomenon for the least energy solutions to nonlinear scalar field equations

We study the existence of least energy solutions to the nonlinear scalar field equation: (1) − Δ u + λ u + V ( x ) u = Q ( x ) | u | p u , u ∈ H 1 ( R N ) , Where V ( x ) , Q ( x ) ∈ L ∞ ( R N ) are real functions satisfying suitable assumptions. By considering the Nehari type constraint N λ := { u ∈ H 1 ( R N ) ∖ { 0 } : ∫ R N ( | ∇ u | 2 + λ | u | 2 + V ( x ) | u | 2 ) d x = ∫ R N Q ( x ) | u | p + 2 d x } , it is shown that (1) exists at least a nontrivial least energy solutions if \\lambda _{*}:=-\\inf \\sigma (-\\Delta +V) $ ]]> λ > λ ∗ := − inf σ ( − Δ + V ) . In this argument, we point out λ ∗ is a critical value for the existence of least energy solutions restricted to N λ . That is, there exists global least energy solutions in N λ if \\lambda _{*} $ ]]> λ > λ ∗ , but not if λ < λ ∗ . Moreover, the asymptotic behavior of least energy solutions as λ → + ∞ is analyzed.

Scalar field equation via the Newman Penrose formalism and separation in the Kerr and Lemaitre-Tolman-Bondi metric

Scalar field equation via the Newman Penrose formalism and separation in the Kerr and Lemaitre-Tolman-Bondi metric

Normalized solutions of the Schrödinger equation with potential

AbstractIn this paper, for dimension and prescribed mass , we consider the following nonlinear scalar field equation with constraint: where is a Lagrange multiplier, . In particular, satisfies mass supercritical and Sobolev subcritical growth. We prove the existence results of the normalized solution and infinitely many normalized solutions to the above system under some proper assumptions on the functions by the mountain pass argument.

Multiplicity of solutions for a scalar field equation involving a fractional p-Laplacian with general nonlinearity

We prove the existence of infinitely many radially symmetric solutions to the problem where , , , and is the fractional p-Laplacian operator. We treat both the cases sp = N and sp<N. The nonlinearity g is a function of Berestycki–Lions type with critical exponential growth if sp = N and critical polynomial growth if sp<N. We also prove the existence of a ground state solution for the same problem.

Anisotropic Fractional Cosmology: K-Essence Theory

In the particular configuration of the scalar field k-essence in the Wheeler–DeWitt quantum equation, for some age in the Bianchi type I anisotropic cosmological model, a fractional differential equation for the scalar field arises naturally. The order of the fractional differential equation is β=2α2α−1. This fractional equation belongs to different intervals depending on the value of the barotropic parameter; when ωX∈[0,1], the order belongs to the interval 1≤β≤2, and when ωX∈[−1,0), the order belongs to the interval 0&lt;β≤1. In the quantum scheme, we introduce the factor ordering problem in the variables (Ω,ϕ) and its corresponding momenta (ΠΩ,Πϕ), obtaining a linear fractional differential equation with variable coefficients in the scalar field equation, then the solution is found using a fractional power series expansion. The corresponding quantum solutions are also given. We found the classical solution in the usual gauge N obtained in the Hamiltonian formalism and without a gauge. In the last case, the general solution is presented in a transformed time T(τ); however, in the dust era we found a closed solution in the gauge time τ.

Multiple bump solutions to logarithmic scalar field equations

Multiple bump solutions to logarithmic scalar field equations

Cosmological solutions of chameleon scalar field model

We investigate cosmological solutions of the chameleon model with a non-minimal coupling between the matter and the scalar field through a conformal factor with gravitational strength. By considering the spatially flat FLRW metric and the matter density as a non-relativistic perfect fluid, we focus on the matter-dominated phase and the late-time accelerated-phase of the universe. In this regard, we manipulate and scrutinize the related field equations for the density parameters of the matter and the scalar fields with respect to the e-folding. Since the scalar field fluctuations depend on the background and the field equations become highly non-linear, we probe and derive the governing equations in the context of various cases of the relation between the kinetic and potential energies of the chameleon scalar field, or indeed, for some specific cases of the scalar field equation of state parameter. Thereupon, we schematically plot those density parameters for two different values of the chameleon non-minimal coupling parameter, and discuss the results. In the both considered phases, we specify that, when the kinetic energy of the chameleon scalar field is much less than its potential energy (i.e., when the scalar field equation of state parameter is ≃-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\simeq - 1 $$\\end{document}), the behavior of the chameleon model is similar to the ΛCDM\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda CDM$$\\end{document} model. Such compatibility suggests that the chameleon model is phenomenologically viable and can be tested with the observational data.

Normalized solutions for scalar field equation involving multiple critical nonlinearities

Abstract This paper concerns the scalar field equation - Δ ⁢ u = λ ⁢ u + | u | q - 2 ⁢ u + a ⁢ | u | 4 ⁢ u + b ⁢ ( I 2 ∗ | u | 5 ) ⁢ | u | 3 ⁢ u in ⁢ ℝ 3 -\Delta u=\lambda u+|u|^{q-2}u+a|u|^{4}u+b(I_{2}\ast|u|^{5})|u|^{3}u\quad\text% {in }\mathbb{R}^{3} under the normalized constraint ∫ ℝ 3 u 2 ⁢ 𝑑 x = c 2 {\int_{\mathbb{R}^{3}}u^{2}\,dx=c^{2}} , where a , b , c &gt; 0 {a,\,b,\,c&gt;0} , 2 &lt; q &lt; 10 3 {2&lt;q&lt;\frac{10}{3}} and I 2 {I_{2}} is the Riesz potential. We prove that for small prescribed mass c the above equation has a positive ground state solution and an infinite sequence of normalized solutions with negative energies tending to zero. Asymptotic properties of ground state solutions as a → 0 + {a\to 0^{+}} and as b → 0 + {b\to 0^{+}} are also studied.