## The Annals of Probability

### On the Lower Tail of Gaussian Seminorms

#### Abstract

Let $E$ be an infinite-dimensional vector space carrying a Gaussian measure $\mu$ with mean 0 and a measurable norm $q$. Let $F(t) := \mu(q \leqslant t)$. By a result of Borell, $F$ is logarithmically concave. But we show that $F'$ may have infinitely many local maxima for norms $q = \sup_n|f_n|/a_n$ where $f_n$ are independent standard normal variables. We also consider Hilbertian norms $q = (\Sigma b_nf^2_n)^{\frac{1}{2}}$ with $b_n > 0, \Sigma b_n < \infty$. Then as $t \downarrow 0$ we can have $F(t) \downarrow 0$ as rapidly as desired, or as slowly as any function which is $o(t^n)$ for all $n$. For $b_n = 1/n^2$ and in a few closely related cases, we find the exact asymptotic behavior of $F$ at 0. For more general $b_n$ we find inequalities bounding $F$ between limits which are not too far apart.

#### Article information

Source
Ann. Probab. Volume 7, Number 2 (1979), 319-342.

Dates
First available in Project Euclid: 19 April 2007

https://projecteuclid.org/euclid.aop/1176995091

Digital Object Identifier
doi:10.1214/aop/1176995091

Mathematical Reviews number (MathSciNet)
MR525057

Zentralblatt MATH identifier
0424.60041

JSTOR