Talk:E8 lattice

I have added chapter "Example definition of integral octonions". This is based on Koca work from 2007 (published on archiv 2005). However my octonion multiplication is different than in Koca work. I am using octonion multiplication obtained from Cayley-Dickson construction from quaternions and sign at e7 is changed. In this way it is easier to remember for me: 123, 145, 167, 246, 275, 374, 365.

The goal of my definition is to have direct definition of octonionic E8 roots - called E8 lattice also.

The abc triads 123, 145, 167, 346, 375, 274, 265 used for E8 roots with real part, are obtained from the above by exchanging 2 and 3 in last for triads.

The pqrs fours 1246, 1257, 1347, 1356, 2345, 2367, 4567 are obtained from above abc triads e.g. by replacing 3 by 46 and 57 in triad 123 which is concluded from 346, 357 triads.

I wonder what are the others integral octonions definitions as said "There are actually seven such maximal orders, one corresponding to each of the seven imaginary units."

Regards, Marek Mitros, Warsaw, Poland mim52@op.pl —Preceding unsigned comment added by Marmit1 (talk • contribs) 10:05, 17 November 2009 (UTC)

Lisi theory -> "E8 theory"

At Talk:An_Exceptionally_Simple_Theory_of_Everything#Requested_move some editors apparently not acquainted with E₈ in other contexts are proposing to move that article to "E8 theory", which I feel would be ambiguous and giving Garrett Lisi's theory excessive weight. Please come and help discuss this. --JWB (talk) 03:56, 26 November 2009 (UTC)

Structure of the Weyl group

The E₈ Weyl group contains a subgroup of index 2, formed by the orientation-preserving symmetries, because it is generated by reflections through the hyperplanes perpendicular to the root vectors. This subgroup contains reflection through the origin because the dimension of the lattice is even. The quotient of this subgroup of index 2 by reflection through the origin is a simple group of order $696729600/4=174182400$. What I have trouble verifying is that this simple group is the orthogonal group denoted O_8+(2). http://brauer.maths.qmul.ac.uk/Atlas/clas/O8p2/ has good information about that orthogonal group. —Preceding unsigned comment added by DavidLHarden (talk • contribs) 18:13, 24 January 2010 (UTC)

Formula

There appears to be a mismatch between the description and the formula: the description says that all coordinates must be integers or all must be half-integers, but the formula allows mixed integer and half-integer coordinates. I don't know the subject or have any references, so I'm leaving the editing to an expert.

Thanks

Virginia-American (talk) 16:22, 5 March 2020 (UTC)

No, it doesn't: $A^{8}\cup B^{8}\neq (A\cup B)^{8}$. --JBL (talk) 16:35, 26 March 2020 (UTC)

Thanks

Virginia-American (talk) 15:34, 29 March 2020 (UTC)