claimstandard

Level exponents equal Artin conductors

Level exponent at qq equals Artin conductor exponent of rℓr_\ell
reduces the level bound to local conductors
Claim·§4.8 A uniform bound for the modular level·inside lemModular level is polynomially bounded in M

Statement (paper)

For every prime qq, the exponent of qq in the primitive level of the weight-two form equals the Artin-conductor exponent at qq of its ℓ\ell-adic representation rℓr_\ell (for q≠ℓq\ne\ell, using r2r_2 at all primes other than 22 and r3r_3 at 22), including the Weil--Deligne monodromy contribution. Moreover, this exponent is zero for every prime q∉Tq\notin T.

In plain English

For each prime qq, the exponent of qq in the primitive level of the weight-two newform equals the Artin-conductor exponent at qq of rℓr_\ell, with the Weil–Deligne monodromy term included. Here r2r_2 is used at primes other than 2 and r3r_3 at 22. This exponent is zero for every prime q∉Tq\notin T.

Why it's here

This turns the bound on the level NN into a bound on local Artin conductors of Galois representations. The compatibility of r2r_2 and r3r_3 with the same newform lets one use whichever representation is coprime to qq at each prime. Later claims then only need to bound conductors at the primes in TT, with the small primes handled by uniform ramification cuts.
Classified standard:
This is local-global compatibility of the Langlands correspondence for weight-two newforms: the level exponent equals the conductor of the Weil–Deligne representation at q≠ℓ (Carayol 1986, building on Deligne, Langlands). Vanishing outside T follows because the representation is unramified there.

Sources

PaperOpen
Section
§4.8 A uniform bound for the modular level
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sections/04-height.tex:1051
Leannot aligned

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