# Equiangular lines and spherical codes in Euclidean space

Balla, I
Draxler, F
Keevash, P
Sudakov, B

January 2018

## Journal:

INVENTIONES MATHEMATICAE

## Last Updated:

2019-10-08T10:53:11.66+01:00

1

211

## DOI:

10.1007/s00222-017-0746-0

179-212

## abstract:

© 2017 Springer-Verlag GmbH Germany A family of lines through the origin in Euclidean space is called equiangular if any pair of lines defines the same angle. The problem of estimating the maximum cardinality of such a family in (Formula presented.) was extensively studied for the last 70 years. Motivated by a question of Lemmens and Seidel from 1973, in this paper we prove that for every fixed angle (Formula presented.) and sufficiently large (Formula presented.) there are at most (Formula presented.) lines in (Formula presented.) with common angle (Formula presented.). Moreover, this bound is achieved if and only if (Formula presented.). Indeed, we show that for all (Formula presented.) and and sufficiently large n, the number of equiangular lines is at most 1.93n. We also show that for any set of k fixed angles, one can find at most (Formula presented.) lines in (Formula presented.) having these angles. This bound, conjectured by Bukh, substantially improves the estimate of Delsarte, Goethals and Seidel from 1975. Various extensions of these results to the more general setting of spherical codes will be discussed as well.

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