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Kunio Hidano

Publications and source records attributed to Kunio Hidano.

18 recordsLinked to original sources
arXiv2022

Global existence for null-form wave equations with data in a Sobolev space of lower regularity and weight

Assuming initial data have small weighted $H^4\times H^3$ norm, we prove global existence of solutions to the Cauchy problem for systems of quasi-linear wave equations in three space dimensions satisfying the null condition of Klainerman. Compared with the work of Christodoulou, our result assumes smallness of data with respect to $H^4\times H^3$ norm having a lower weight. Our proof uses the space-time $L^2$ estimate due to Alinhac for some special derivatives of solutions to variable-coefficient wave equations. It also uses the conformal energy estimate for inhomogeneous wave equation $\Box u=F$. A new observation made in this paper is that, in comparison with the proofs of Klainerman and Hörmander, we can limit the number of occurrences of the generators of hyperbolic rotations or dilations in the course of a priori estimates of solutions. This limitation allows us to obtain global solutions for radially symmetric data, when a certain norm with considerably low weight is small enough.

math.AP↗
arXiv2022

Global existence for a system of multiple-speed wave equations violating the null condition

We discuss the Cauchy problem for a system of semilinear wave equations in three space dimensions with multiple wave speeds. Though our system does not satisfy the standard null condition, we show that it admits a unique global solution for any small and smooth data. This generalizes a preceding result due to Pusateri and Shatah. The proof is carried out by the energy method involving a collection of generalized derivatives. The multiple wave speeds disable the use of the Lorentz boost operators, and our proof therefore relies upon the version of Klainerman and Sideris. Due to the presence of nonlinear terms violating the standard null condition, some of components of the solution may have a weaker decay as $t\to\infty$, which makes it difficult even to establish a mildly growing (in time) bound for the high energy estimate. We overcome this difficulty by relying upon the ghost weight energy estimate of Alinhac and the Keel-Smith-Sogge type $L^2$ weighted space-time estimate for derivatives.

math.AP↗
arXiv2022

Global existence and blow up for systems of nonlinear wave equations related to the weak null condition

We discuss how the higher-order term $|u|^q$ $(q>1+2/(n-1))$ has nontrivial effects in the lifespan of small solutions to the Cauchy problem for the system of nonlinear wave equations $$ \partial_t^2 u-Δu=|v|^p, \qquad \partial_t^2 v-Δv=|\partial_t u|^{(n+1)/(n-1)} +|u|^q $$ in $n\,(\geq 2)$ space dimensions. We show the existence of a certain "critical curve" on the $pq$-plane such that for any $(p,q)$ $(p,q>1)$ lying below the curve, nonexistence of global solutions occurs, whereas for any $(p,q)$ $(p>1+3/(n-1),\,q>1+2/(n-1))$ lying exactly on it, this system admits a unique global solution for small data. When $n=3$, the discussion for the above system with $(p,q)=(3,3)$, which lies on the critical curve, has relevance to the study on systems satisfying the weak null condition, and we obtain a new result of global existence for such systems. Moreover, in the particular case of $n=2$ and $p=4$ it is observed that no matter how large $q$ is, the higher-order term $|u|^q$ never becomes negligible and it essentially affects the lifespan of small solutions.

math.AP↗
arXiv2019

Remarks on a system of quasi-linear wave equations in $3$D satisfying the weak null condition

We give an alternative proof of the global existence result originally due to Hidano and Yokoyama for the Cauchy problem for a system of quasi-linear wave equations in three space dimensions satisfying the weak null condition. The feature of the new proof lies in that it never uses the Lorentz boost operator in the energy integral argument. The proof presented here has an advantage over the former one in that the assumption of compactness of the support of data can be eliminated and the amount of regularity of data can be lowered in a straightforward manner. A recent result of Zha for the scalar unknowns is also refined.

math.AP↗
arXiv2018

Global existence for a system of quasi-linear wave equations in $3$D satisfying the weak null condition

We show global existence of small solutions to the Cauchy problem for a system of quasi-linear wave equations in three space dimensions. The feature of the system lies in that it satisfies the weak null condition, though we permit the presence of some quadratic nonlinear terms which do not satisfy the null condition. Due to the presence of such quadratic terms, the standard argument no longer works for the proof of global existence. To get over this difficulty, we extend the ghost weight method of Alinhac so that it works for the system under consideration. The original theorem of Alinhac for the scalar unknowns is also refined.

math.AP↗
arXiv2018

Space-time $L^2$ estimates, regularity and almost global existence for elastic waves

In this paper, we first establish a kind of weighted space-time $L^2$ estimate, which belongs to Keel-Smith-Sogge type estimates, for perturbed linear elastic wave equations. This estimate refines the corresponding one established by the second author [J. Differential Equations 263(2017), 1947--1965] and is proved by combining the methods in the former paper, the first author, Wang and Yokoyama's paper [Adv. Differential Equations 17 (2012), 267--306], and some new ingredients. Then together with some weighted Sobolev inequalities, this estimate is used to show a refined version of almost global existence of classical solutions for nonlinear elastic waves with small initial data. Compared with former almost global existence results for nonlinear elastic waves due to John [Comm. Pure Appl. Math. 41 (1988) 615--666], Klaierman-Sideris [Comm. Pure Appl. Math. 49 (1996) 307--321], the main innovation of our one is that it considerably improves the amount of regularity of initial data, i.e., the Sobolev regularity of initial data is assumed to be the smallest among all the admissible Sobolev spaces of integer order in the standard local existence theory. Finally, in the radially symmetric case, we establish the almost global existence of a low regularity solution for every small initial data in $H^3\times H^2$.

math.AP↗
arXiv2018

Weighted fractional chain rule and nonlinear wave equations with minimal regularity

We consider the local well-posedness for 3-D quadratic semi-linear wave equations with radial data: $\Box u = a |\partial_t u|^2+b|\nabla_x u|^2$, $u(0,x)=u_0(x)\in H^{s}_{\mathrm{rad}}$, $\partial_t u(0,x)=u_1(x)\in H^{s-1}_{\mathrm{rad}}$. It has been known that the problem is well-posed for $s\ge 2$ and ill-posed for $s<3/2$. In this paper, we prove unconditional well-posedness up to the scaling invariant regularity, that is to say, for $s>3/2$ and thus fill the gap which was left open for many years. For the purpose, we also obtain a weighted fractional chain rule, which is of independent interest. Our method here also works for a class of nonlinear wave equations with general power type nonlinearities which contain the space-time derivatives of the unknown functions. In particular, we prove the Glassey conjecture in the radial case, with minimal regularity assumption.

math.AP↗
arXiv2017

Global low regularity solutions for nonlinear elastic waves

We study the Cauchy problem for 3-D nonlinear elastic waves satisfying the null condition with low regularity initial data. In the radially symmetric case, we prove the global existence of a low regularity solution for every small data in $H^3\times H^2$ with a low weight.

math.AP↗
arXiv2017

Fractional derivatives of composite functions and the Cauchy problem for the nonlinear half wave equation

We show new results of wellposedness for the Cauchy problem for the half wave equation with power-type nonlinear terms. For the purpose, we propose two approaches on the basis of the contraction-mapping argument. One of them relies upon the $L_t^q L_x^\infty$ Strichartz-type estimate together with the chain rule of fairly general fractional orders. This chain rule has a significance of its own. Furthermore, in addition to the weighted fractional chain rule established in Hidano, Jiang, Lee, and Wang (arXiv:1605.06748v1 [math.AP]), the other approach uses weighted space-time $L^2$ estimates for the inhomogeneous equation which are recovered from those for the second-order wave equation. In particular, by the latter approach we settle the problem left open in Bellazzini, Georgiev, and Visciglia (arXiv:1611.04823v1 [math.AP]) concerning the local wellposedness in $H^{s}_{\rm rad}({\mathbb R}^n)$ with $s>1/2$.

math.AP↗
arXiv2017

Regularity and lifespan of small solutions to systems of quasi-linear wave equations with multiple speeds,I: almost global existence

In this paper, we show almost global existence of small solutions to the Cauchy problem for symmetric system of wave equations with quadratic (in 3D) or cubic (in 2D) nonlinear terms and multiple propagation speeds. To measure the size of initial data, we employ a weighted Sobolev norm whose regularity index is the smallest among all the admissible Sobolev norms of integer order. We must overcome the difficulty caused by the absence of the $H^1$-$L^p$ Klainerman-Sobolev type inequality, in order to obtain a required a priori bound in the low-order Sobolev norm. The introduction of good substitutes for this inequality is therefore at the core of this paper. Using the idea of showing the well-known Ladyženskaja inequality, we prove some weighted inequalities, which, together with the generalized Strauss inequality, play a role as the good substitute.

math.AP↗
arXiv2015

Combined effects of two nonlinearities in lifespan of small solutions to semi-linear wave equations

This paper investigates the combined effects of two distinctive power-type nonlinear terms (with parameters $p,q>1$) in the lifespan of small solutions to semi-linear wave equations. We determine the full region of $(p,q)$ to admit global existence of small solutions, at least for spatial dimensions $n=2, 3$. Moreover, for many $(p,q)$ when there is no global existence, we obtain sharp lower bound of the lifespan, which is of the same order as the upper bound of the lifespan.

math.AP↗
arXiv2015

Life span of small solutions to a system of wave equations

We study the Cauchy problem with small initial data for a system of semilinear wave equations $\square u = |v|^p$, $\square v = |\partial_t u|^p$ in $n$-dimensional space. When $n \geq 2$, we prove that blow-up can occur for arbitrarily small data if $(p, q)$ lies below a curve in $p$-$q$ plane. On the other hand, we show a global existence result for $n=3$ which asserts that a portion of the curve is in fact the borderline between global-in-time existence and finite time blow-up. We also estimate the maximal existence time and get an upper bound, which is sharp at least for $(n, p, q)=(2, 2, 2)$ and $(3, 2, 2)$.

math.AP↗
arXiv2011

On almost global existence and local well-posedness for some 3-D quasi-linear wave equations

We study the Cauchy problem for a quasilinear wave equation with low-regularity data. A space-time $L^2$ estimate for the variable coefficient wave equation plays a central role for this purpose. Assuming radial symmetry, we establish the almost global existence of a strong solution for every small initial data in $H^2 \times H^1$. We also show that the initial value problem is locally well-posed.

math.AP↗
arXiv2011

The Glassey conjecture with radially symmetric data

In this paper, we verify the Glassey conjecture in the radial case for all spatial dimensions, which states that, for the nonlinear wave equations of the form $\Box u=|\nabla u|^p$, the critical exponent to admit global small solutions is given by $p_c=1+\frac{2}{n-1}$. Moreover, we are able to prove the existence results with low regularity assumption on the initial data and extend the solutions to the sharp lifespan. The main idea is to exploit the trace estimates and KSS type estimates.

math.AP↗
arXiv2009

On Abstract Strichartz Estimates and the Strauss Conjecture for Nontrapping Obstacles

The purpose of this paper is to show how local energy decay estimates for certain linear wave equations involving compact perturbations of the standard Laplacian lead to optimal global existence theorems for the corresponding small amplitude nonlinear wave equations with power nonlinearities. To achieve this goal, at least for spatial dimensions $n=3$ and 4, we shall show how the aforementioned linear decay estimates can be combined with "abstract Strichartz" estimates for the free wave equation to prove corresponding estimates for the perturbed wave equation when $n\ge3$. As we shall see, we are only partially successful in the latter endeavor when the dimension is equal to two, and therefore, at present, our applications to nonlinear wave equations in this case are limited.

math.AP↗
arXiv2007

Weighted HLS inequalities for radial functions and Strichartz estimates for wave and Schroedinger equations

This paper is concerned with derivation of the global or local in time Strichartz estimates for radially symmetric solutions of the free wave equation from some Morawetz-type estimates via weighted Hardy-Littlewood-Sobolev (HLS) inequalities. In the same way we also derive the weighted end-point Strichartz estimates with gain of derivatives for radially symmetric solutions of the free Schroedinger equation. The proof of the weighted HLS inequality for radially symmetric functions involves an application of the weighted inequality due to Stein and Weiss and the Hardy-Littlewood maximal inequality in the weighted Lebesgue space due to Muckenhoupt. Under radial symmetry we get significant gains over the usual HLS inequality and Strichartz estimate.

math.AP↗
arXiv2007

Nonlinear Schroedinger equations with radially symmetric data of critical regularity

This paper is concerned with the global existence of small solutions to pure-power nonlinear Schroedinger equations subject to radially symmetric data with critical regularity. Under radial symmetry we focus our attention on the case where the power of nonlinearity is somewhat smaller than the pseudoconformal power and the initial data belong to the scale-invariant homogeneous Sobolev space. In spite of the negative-order differentiability of initial data the nonlinear Schroedinger equation has global in time solutions provided that the initial data have the small norm. The key ingredient in the proof of this result is an effective use of global weighted smoothing estimates specific to radially symmetric solutions.

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