A new series of axial algebras of Monster type (2 η, η)

We construct a new series of n²-dimensional axial algebras of Monster type (2 η, η). They arise as subalgebras A of the Matsuo algebras Mη(-On+1+(3)), generated by single and double axes. Also, we address the question of when these algebras are simple. While we do not solve this question, we formulate three concrete conjectures based on the calculation, using the computer algebra system GAP, of the roots of the determinant of the Gram matrix of the Frobenius form on A for several small values of n.