<p>The Lang-Trotter conjecture on primitive points is the analogue for elliptic curves of Artin’s conjecture on primitive roots. Indeed, if we have an elliptic curve <i>E</i> over <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\mathbb Q\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="double-struck">Q</mi> </math></EquationSource> </InlineEquation> with a rational point <i>P</i> of infinite order, we may count the primes <i>p</i> of good reduction for which <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\((P \bmod p)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>P</mi> <mspace width="0.277778em" /> <mo>mod</mo> <mspace width="0.277778em" /> <mi>p</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> generates <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(E(\mathbb F_p)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>E</mi> <mo stretchy="false">(</mo> <msub> <mi mathvariant="double-struck">F</mi> <mi>p</mi> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. In this work, we formulate and investigate two natural variants of the Lang-Trotter conjecture. For one of them, we require that the group <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(E(\mathbb F_p)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>E</mi> <mo stretchy="false">(</mo> <msub> <mi mathvariant="double-struck">F</mi> <mi>p</mi> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and its subgroup <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(&lt; (P \bmod p)&gt;\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>&lt;</mo> <mo stretchy="false">(</mo> <mi>P</mi> <mspace width="0.277778em" /> <mo>mod</mo> <mspace width="0.277778em" /> <mi>p</mi> <mo stretchy="false">)</mo> <mo>&gt;</mo> </mrow> </math></EquationSource> </InlineEquation> have the same exponent, namely the cyclic subgroup is as large as possible. We conjecture that the set of primes <i>p</i> such that this condition holds admits a natural density, whose value is a rational multiple of the product over all primes <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\ell \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ℓ</mi> </math></EquationSource> </InlineEquation> of the natural densities (which we prove to exist and be rational) of those <i>p</i> such that the exponents of <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(E(\mathbb F_p)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>E</mi> <mo stretchy="false">(</mo> <msub> <mi mathvariant="double-struck">F</mi> <mi>p</mi> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(&lt; (P \bmod p)&gt;\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>&lt;</mo> <mo stretchy="false">(</mo> <mi>P</mi> <mspace width="0.277778em" /> <mo>mod</mo> <mspace width="0.277778em" /> <mi>p</mi> <mo stretchy="false">)</mo> <mo>&gt;</mo> </mrow> </math></EquationSource> </InlineEquation> have the same <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\ell \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ℓ</mi> </math></EquationSource> </InlineEquation>-adic valuation. Numerical examples support the validity of our conjectures.</p>

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Two natural variants of the Lang-Trotter conjecture on primitive points for elliptic curves

  • Alexandre Benoist,
  • Antonella Perucca

摘要

The Lang-Trotter conjecture on primitive points is the analogue for elliptic curves of Artin’s conjecture on primitive roots. Indeed, if we have an elliptic curve E over \(\mathbb Q\) Q with a rational point P of infinite order, we may count the primes p of good reduction for which \((P \bmod p)\) ( P mod p ) generates \(E(\mathbb F_p)\) E ( F p ) . In this work, we formulate and investigate two natural variants of the Lang-Trotter conjecture. For one of them, we require that the group \(E(\mathbb F_p)\) E ( F p ) and its subgroup \(< (P \bmod p)>\) < ( P mod p ) > have the same exponent, namely the cyclic subgroup is as large as possible. We conjecture that the set of primes p such that this condition holds admits a natural density, whose value is a rational multiple of the product over all primes \(\ell \) of the natural densities (which we prove to exist and be rational) of those p such that the exponents of \(E(\mathbb F_p)\) E ( F p ) and \(< (P \bmod p)>\) < ( P mod p ) > have the same \(\ell \) -adic valuation. Numerical examples support the validity of our conjectures.