Equivalence conditions for on-diagonal upper bounds of heat kernels on self-similar spaces

We obtain the equivalence conditions for an on-diagonal upper bound of heat kernels on self-similar measure energy spaces. In particular, this upper bound of the heat kernel is equivalent to the discreteness of the spectrum of the generator of the Dirichlet form, and to the global Poincaré inequality. The key ingredient of the proof is to obtain the Nash inequality from the global Poincaré inequality. We give two examples of families of spaces where the global Poincaré inequality is easily derived. They are the post-critically finite (p.c.f.) self-similar sets with harmonic structure and the products of self-similar measure energy spaces.     

A new approach to pointwise heat kernel upper bounds on doubling metric measure spaces

On doubling metric measure spaces endowed with a strongly local regular Dirichlet form, we show some characterisations of pointwise upper bounds of the heat kernel in terms of global scale-invariant inequalities that correspond respectively to the Nash inequality and to a Gagliardo–Nirenberg type inequality when the volume growth is polynomial. This yields a new proof and a generalisation of the well-known equivalence between classical heat kernel upper bounds and relative Faber–Krahn inequalities or localised Sobolev or Nash inequalities. We are able to treat more general pointwise estimates, where the heat kernel rate of decay is not necessarily governed by the volume growth. A crucial role is played by the finite propagation speed property for the associated wave equation, and our main result holds for an abstract semigroup of operators satisfying the Davies–Gaffney estimates.     

Off-diagonal upper estimates for the heat kernel of the Dirichlet forms on metric spaces

We give equivalent characterizations for off-diagonal upper bounds of the heat kernel of a regular Dirichlet form on the metric measure space, in two settings: for the upper bounds with the polynomial tail (typical for jump processes) and for the upper bounds with the exponential tail (for diffusions). Our proofs are purely analytic and do not use the associated Hunt process.     

Class of tight bounds on the Q‐function with closed‐form upper bound on relative error

In this paper, we propose a novel class of parametric bounds on the Q‐function, which are lower bounds for 1 ≤ a < 3 and x > x_t = (a (a‐1) / (3‐a))^1/2, and upper bound for a = 3. We prove that the lower and upper bounds on the Q‐function can have the same analytical form that is asymptotically equal, which is a unique feature of our class of tight bounds. For the novel class of bounds and for each particular bound from this class, we derive the beneficial closed‐form expression for the upper bound on the relative error. By comparing the bound tightness for moderate and large argument values not only numerically, but also analytically, we demonstrate that our bounds are tighter compared with the previously reported bounds of similar analytical form complexity.     

Decroissance exponentielle du noyau de la chaleur sur la diagonale (I)

Summary We give examples based upon large deviation's theory where the heat kernel of a degenerate diffusion has an exponential decay over the diagonal. Using Malliavin calculus, we give conditions for a more generalized heat kernel to have an exponential decay over the diagonal. We give lower bound in some particular case by using the Bismut's condition.     

Asymptotic bounds for the expected L error of a multivariate kernel density estimator

The kernel estimator of a multivariate probability density function is studied. An asymptotic upper bound for the expected L¹ error of the estimator is derived. An asymptotic lower bound result and a formula for the exact asymptotic error are also given. The goodness of the smoothing parameter value derived by minimizing an explicit upper bound is examined in numerical simulations that consist of two different experiments. First, the L¹ error is estimated using numerical integration and, second, the effect of the choice of the smoothing parameter in discrimination tasks is studied.     

Sharp bounds for the first eigenvalue and the torsional rigidity related to some anisotropic operators

In this paper we prove a sharp upper bound for the first Dirichlet eigenvalue of a class of nonlinear elliptic operators which includes the operator , that is the p‐Laplacian, and , namely the pseudo‐p‐Laplacian. Moreover we prove a stability result by means of a suitable isoperimetric deficit. Finally, we give a sharp lower bound for the anisotropic p‐torsional rigidity.     

A Note on the Transition Density Estimate for Some Diffusion Process on a d–Set

The paper is devoted to transition density estimates for some diffusion process on a d–set. Starting with some local regular Dirichlet form, it is shown, that the associated diffusion satisfies certain upper and lower estimates.      

Sharp heat kernel bounds and entropy in metric measure spaces

We establish the sharp upper and lower bounds of Gaussian type for the heat kernel in the metric measure space satisfying the RCD(0, N)(equivalently, RCD~*(0, N), condition with N∈N\ {1} and having the maximum volume growth, and then show its application on the large-time asymptotics of the heat kernel, sharp bounds on the(minimal) Green function, and above all, the large-time asymptotics of the Perelman entropy and the Nash entropy, where for the former the monotonicity of the Perelman entropy is proved. The results generalize the corresponding ones in the Riemannian manifolds, and some of them appear more explicit and sharper than the ones in metric measure spaces obtained recently by Jiang et al.(2016).     

Dirichlet forms and associated heat kernels on the Cantor set induced by random walks on trees

Transient random walk on a tree induces a Dirichlet form on its Martin boundary, which is the Cantor set. The procedure of the inducement is analogous to that of the Douglas integral on S¹ associated with the Brownian motion on the unit disk. In this paper, those Dirichlet forms on the Cantor set induced by random walks on trees are investigated. Explicit expressions of the hitting distribution (harmonic measure) ν and the induced Dirichlet form on the Cantor set are given in terms of the effective resistances. An intrinsic metric on the Cantor set associated with the random walk is constructed. Under the volume doubling property of ν with respect to the intrinsic metric, asymptotic behaviors of the heat kernel, the jump kernel and moments of displacements of the process associated with the induced Dirichlet form are obtained. Furthermore, relation to the noncommutative Riemannian geometry is discussed.     

Rough hypoellipticity for the heat equation in Dirichlet spaces

This paper aims at proving the local boundedness and continuity of solutions of the heat equation in the context of Dirichlet spaces under some rather weak additional assumptions. We consider symmetric local regular Dirichlet forms, which satisfy mild assumptions concerning (1) the existence of cut-off functions, (2) a local ultracontractivity hypothesis, and (3) a weak off-diagonal upper bound. In this setting, local weak solutions of the heat equation, and their time derivatives, are shown to be locally bounded; they are further locally continuous, if the semigroup admits a locally continuous density function. Applications of the results are provided including discussions on the existence of locally bounded heat kernel; $L^{\infty }$ structure results for ancient (local weak) solutions of the heat equation.     

Upper bounds on the length of the shortest closed geodesic on simply connected manifolds

The subject of this paper is upper bounds on the length of the shortest closed geodesic on simply connected manifolds with non-trivial second homology group. We will give three estimates. The first estimate will explicitly depend on volume and the upper bound for the sectional curvature; the second estimate will depend on diameter, a positive lower bound for the volume, and on the (possibly negative) lower bound on sectional curvature; the third estimate will depend on diameter, on a (possibly negative) lower bound for the sectional curvature and on a lower bound for the simply-connectedness radius. The technique that we develop in order to obtain the last result will also enable us to estimate the homotopy distance between any two closed curves on compact simply connected manifolds of sectional curvature bounded from below and diameter bounded from above. More precisely, let c be a constant such that any metric ball of radius is simply connected. There exists a homotopy connecting any two closed curves such that the length of the trajectory of the points during this homotopy has an upper bound in terms of the lower bound of the curvature, the upper bound of diameter and c. Received November 10, 1997; in final form June 23, 1998     

Comparison inequalities for heat semigroups and heat kernels on metric measure spaces

We prove a certain inequality for a subsolution of the heat equation associated with a regular Dirichlet form. As a consequence of this inequality, we obtain various interesting comparison inequalities for heat semigroups and heat kernels, which can be used for obtaining pointwise estimates of heat kernels. As an example of application, we present a new method of deducing sub-Gaussian upper bounds of the heat kernel from on-diagonal bounds and tail estimates.     

Topological lower bounds on the distance between area preserving diffeomorphisms

Area preserving diffeomorphisms of the 2-disk which are Identity near the boundary form a group which can be equipped, using theL ²-norm on its Lie algebra, with a right invariant metric. In this paper we give a lower bound on the distance between diffeomorphisms which is invariant under area preserving changes of coordinates and which improves the lower bound induced by the Calabi invariant. In the case of renormalizable and infinitely renormalizable maps, our estimate can be improved and computed.     

Intrinsic metrics for non-local symmetric Dirichlet forms and applications to spectral theory

We present a study of what may be called an intrinsic metric for a general regular Dirichlet form. For such forms we then prove a Rademacher type theorem. For strongly local forms we show existence of a maximal intrinsic metric (under a weak continuity condition) and for Dirichlet forms with an absolutely continuous jump kernel we characterize intrinsic metrics by bounds on certain integrals. We then turn to applications on spectral theory and provide for (measure perturbation of) general regular Dirichlet forms an Allegretto–Piepenbrink type theorem, which is based on a ground state transform, and a Shnol' type theorem. Our setting includes Laplacian on manifolds, on graphs and α-stable processes.     

Upper bounds for permanents of (1, − 1)-matrices

Let Ω _n denote the set of alln×n (1, ? 1)-matrices. In 1974 E. T. H. Wang posed the following problems: Is there a decent upper bound for |perA| whenAσΩ _n is nonsingular? We recently conjectured that the best possible bound is the permanent of the matrix with exactlyn?1 negative entries in the main diagonal, and affirmed that conjecture by the study of a large class of matrices in Ω _n . Here we prove that this conjecture also holds for another large class of (1, ?1)-matrices which are all nonsingular. We also give an upper bound for the permanents of a class of matrices in Ω _n which are not all regular.     

Some remarks on essential self‐adjointness and ultracontractivity of a class of singular elliptic operators

We study the properties of essential self‐adjointness on C^∞_c (ℝ^N ) and semigroup ultracontractivity of a class of singular second order elliptic operators defined in L² (ℝ^N , σ^{–a –N} (x) dx) with Dirichlet boundary conditions, where a, b ∈ ℝ and σ: ℝ^N → (0, ∞) is a C^∞‐function satisfying c^‐1(1 + |x |) ≤ σ (x) ≤ c (1 + |x |) (x ∈ ℝN). We also obtain sharp short time upper and lower diagonal bounds on the heat kernel of e –^Ht. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectral asymptotics for Laplacians on self-similar sets

Given a self-similar Dirichlet form on a self-similar set, we first give an estimate on the asymptotic order of the associated eigenvalue counting function in terms of a ‘geometric counting function’ defined through a family of coverings of the self-similar set naturally associated with the Dirichlet space. Secondly, under (sub-)Gaussian heat kernel upper bound, we prove a detailed short time asymptotic behavior of the partition function, which is the Laplace-Stieltjes transform of the eigenvalue counting function associated with the Dirichlet form. This result can be applicable to a class of infinitely ramified self-similar sets including generalized Sierpinski carpets, and is an extension of the result given recently by B.M. Hambly for the Brownian motion on generalized Sierpinski carpets. Moreover, we also provide a sharp remainder estimate for the short time asymptotic behavior of the partition function.     

Tight bounds for the number of edge guards for spiral polygons

In this paper we give tight lower and upper bounds for the number of edge guards required for covering spiral polygons. We have proved that [(n + 2)/5]edge guards are necessary and sufficient to cover a spiral polygon. It has been shown by Aggarwal [2] that [(n + 2)/5]diagonal guards are necessary and sufficient to cover a spiral polygon. Edge guards are more restrictive than diagonal guards. Hence the previous theorem can be got as a corollary using our theorem. The necessary condition of the edge guard problem for spiral polygons has not been investigated although the diagonal guard problem for the same has been solved [2]. The necessary proof of the edge guard problem follows from the necessary condition of the diagonal guard problem but we have given an alternate proof of necessity.     

Subexponential behaviour of the Dirichlet heat kernel

We obtain a formula for the asymptotic behaviour of the Dirichlet heat kernel for large time in terms of the survival probability of a Brownian motion, under the assumption that the latter decays subexponentially for large time. We also obtain a lower bound for the Dirichlet heat kernel for arbitrary open and connected sets in Euclidean space.