We consider operators $ - \Delta + X $ , where $ X $ is a constant vector field, in a bounded domain, and show spectral instability when the domain is expanded by scaling. More generally, we consider semiclassical elliptic boundary value problems which exhibit spectral instability for small values of the semiclassical parameter $h$ , which should be thought of as the reciprocal of the Péclet constant. This instability is due to the presence of the boundary: just as in the case of $ - \Delta + X $ , some of our operators are normal when considered on $\mathbb{R}^d$ . We characterize the semiclassical pseudospectrum of such problems as well as the areas of concentration of quasimodes. As an application, we prove a result about exit times for diffusion processes in bounded domains. We also demonstrate instability for a class of spectrally stable nonlinear evolution problems that are associated with these elliptic operators.

Given a prime $p\gt 2$ , an integer $h\geq 0$ , and a wide open disk $U$ in the weight space $ \mathcal{W} $ of ${\mathbf{GL} }_{2} $ , we construct a Hecke–Galois-equivariant morphism ${ \Psi }_{U}^{(h)} $ from the space of analytic families of overconvergent modular symbols over $U$ with bounded slope $\leq h$ , to the corresponding space of analytic families of overconvergent modular forms, all with ${ \mathbb{C} }_{p} $ -coefficients. We show that there is a finite subset $Z$ of $U$ for which this morphism induces a $p$ -adic analytic family of isomorphisms relating overconvergent modular symbols of weight $k$ and slope $\leq h$ to overconvergent modular forms of weight $k+ 2$ and slope  $\leq h$ .

Let $X$ be a smooth proper curve over a finite field of characteristic $p$ . We prove a product formula for $p$ -adic epsilon factors of arithmetic $\mathscr{D}$ -modules on $X$ . In particular we deduce the analogous formula for overconvergent $F$ -isocrystals, which was conjectured previously. The $p$ -adic product formula is a counterpart in rigid cohomology of the Deligne–Laumon formula for epsilon factors in $\ell$ -adic étale cohomology (for $\ell \neq p$ ). One of the main tools in the proof of this $p$ -adic formula is a theorem of regular stationary phase for arithmetic $\mathscr{D}$ -modules that we prove by microlocal techniques.

Let $k$ be a base commutative ring, $R$ a commutative ring of coefficients, $X$ a quasi-compact quasi-separated $k$ -scheme, and $A$ a sheaf of Azumaya algebras over $X$ of rank $r$ . Under the assumption that $1/r\in R$ , we prove that the noncommutative motives with $R$ -coefficients of $X$ and $A$ are isomorphic. As an application, we conclude that a similar isomorphism holds for every $R$ -linear additive invariant. This leads to several computations. Along the way we show that, in the case of finite-dimensional algebras of finite global dimension, all additive invariants are nilinvariant.