arXiv subjects

Miłosz Baraniewicz

Publications and source records attributed to Miłosz Baraniewicz.

4 recordsLinked to original sources

arXiv2026

Smoothing on $L^1$ for ground state transformed semigroups in non-local settings

We study the $L^1$-smoothing properties for a broad class of semigroups arising from the ground state transformation of Schrödinger semigroups with confining potentials associated with non-local Lévy operators, for which (asymptotic) ultracontractivity and hypercontractivity fail. Our work is inspired by Talagrand's convolution conjecture in the discrete cube setting, as well as by subsequent developments on the classical Ornstein--Uhlenbeck semigroup. The estimates we provide exhibit a clear dependence on the potential and the Lévy measure defining the kinetic term operator, and they yield a description of the semigroups' action on $L^1$ in terms of Orlicz spaces. Our framework is quite general, encompassing fractional and relativistic Laplacians as kinetic operators. The results are illustrated by numerous examples demonstrating that the $L^1$-regularizing effects become stronger as $t \uparrow \infty$.

math.FA↗

arXiv2024

Ground state decay for Schrödinger operators with confining potentials

We give two-sided estimates of a ground state for Schrödinger operators with confining potentials. We propose a semigroup approach, based on resolvent and the Feynman--Kac formula, which leads to a new, rather short and direct proof. Our results take the sharpest form for slowly varying, radial and increasing potentials.

math.PR↗

arXiv2023

Integral kernels of Schrödinger semigroups with nonnegative locally bounded potentials

We give the upper and the lower estimates of heat kernels for Schrödinger operators $H=-Δ+V$, with nonnegative and locally bounded potentials $V$ in $\mathbb{R}^d$, $d \geq 1$. We observe a factorization: the contribution of the potential is described separately for each spatial variable, and the interplay between the spatial variables is seen only through the Gaussian kernel - optimal in the lower bound and nearly optimal in the upper bound. In some regimes we observe the exponential decay in time with the rate corresponding to the bottom of the spectrum of $H$. Our estimates identify in a fairly informative and uniform way the dependence of the potential $V$ and the dimension $d$. The upper estimate is more local; it applies to general potentials, including confining and decaying ones, even if they are non-radial, and mixtures. The lower bound is specialized to confining case, and the contribution of the potential is described in terms of its radial upper profile. Our results take the sharpest form for confining potentials that are comparable to radial monotone profiles with sufficiently regular growth - in this case they lead to two-sided qualitatively sharp estimates. In particular, we describe the large-time behaviour of nonintrinsically ultracontractive Schrödinger semigroups - this problem was open for a long time. The methods we use combine probabilistic techniques with analytic ideas. We propose a new effective approach which leads us to short and direct proofs.

math.FA↗

arXiv2022

Exponential densities and compound Poisson measures

We prove estimates at infinity of convolutions $f^{n\star}$ and densities of the corresponding compound Poisson measures for a class of radial decreasing densities on $\mathbb{R}^d$, $d \geq 1$, which are not convolution equivalent. Existing methods and tools are limited to the situation in which the convolution $f^{2\star}(x)$ is comparable to initial density $f(x)$ at infinity. We propose a new approach which allows one to break this barrier. We focus on densities which are products of exponential functions and smaller order terms -- they are common in applications. In the case when the smaller order term is polynomial estimates are given in terms of the generalized Bessel function. Our results can be seen as the first attempt to understand the intricate asymptotic properties of the compound Poisson and more general infinitely divisible measures constructed for such densities.

math.PR↗