Atlas › Modular forms › Weight 2 › Level 86 › 86.2.a

Newspace 86.2.a: $S_{2}^{\mathrm{new}}(\Gamma_0(86))$

Newforms

Label	Dim	Coefficient field	Trace form	AL signs	Sign	CM	Elliptic curve
86.2.a.a	2	$\mathbb{Q}(\sqrt{21})$	$2q - 2q^{2} - q^{3} + 2q^{4} + 3q^{5} + q^{6} + 4q^{7} + O(q^{8})$	+ −	$+1$
86.2.a.b	2	$\mathbb{Q}(\sqrt{5})$	$2q + 2q^{2} + q^{3} + 2q^{4} - 3q^{5} + q^{6} + O(q^{8})$	− +	$+1$

Hecke characteristic polynomials

The eigenvalue of $T = T_{3} + 3T_{5}$ generates each orbit's coefficient field; on the newspace its characteristic polynomial factors over $\mathbb{Q}$ as one irreducible factor per orbit:

Orbit	Characteristic polynomial of $T$
86.2.a.a	$x^{2} - 8x - 5$
86.2.a.b	$x^{2} + 8x + 11$

Dimensions

Newforms $S_{2}^{\mathrm{new}}(\Gamma_0(86))$	4
Old forms	6
Cusp forms $S_{2}(\Gamma_0(86))$	10
Eisenstein series $E_{2}(\Gamma_0(86))$	3
Modular forms $M_{2}(\Gamma_0(86))$	13

Decomposition of the old subspace

$S_{2}^{\mathrm{old}}(\Gamma_0(86)) =$ $S_{2}^{\mathrm{new}}(\Gamma_0(43))^{\oplus 2}$

Provenance

Stored in the atlas: computed by Sagebrush's modular symbols engine in 0.092 s (one thread) and proven: the dimensions are certified, and the characteristic polynomial of $T$ over $\mathbb{Z}$ is reconstructed by CRT past a rigorous coefficient bound.

The engine's checks

dim M^+ at levels [1, 2, 43, 86]: [0, 1, 4, 13] (certified at ell = 2147483647)
T = [(3, 1), (5, 3)]; h of degree 4 = 1 x 4 (phi(ord eps) x dim S_k^new); 1 primes, 0 rejected

Open in the notebook · JSON · stored data

Recompute it yourself

In Sage mode at sagebrush.space (or npx sagebrush --sage):

newform_orbits(86, 2)

With the Rust engine (source), in engine/:

cargo run --release -p sagebrush-web --example atlas -- 86:2 1000

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