Probing proton–electron mass ratio variations using high-precision $$H_2$$ Lyman lines

Abstract We probe potential variations of the proton-to-electron mass ratio ( $$\mu $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>μ</mml:mi> </mml:math> ) using high-resolution H $$_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>2</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> Lyman transitions in the white dwarf GD 133, observed with the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS). White dwarf atmospheres provide a powerful laboratory for testing fundamental physics in strong gravitational fields. Applying a self-consistent spectral analysis, we obtain a tight constraint of $$\Delta \mu /\mu = (0.02 \pm 0.09)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:mi>μ</mml:mi> <mml:mo>/</mml:mo> <mml:mi>μ</mml:mi> <mml:mo>=</mml:mo> <mml:mo>(</mml:mo> <mml:mn>0.02</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.09</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> in a gravitational potential approximately $$10^{4}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>4</mml:mn> </mml:msup> </mml:math> times stronger than that of Earth. The measured uncertainty implies that any variation of $$\mu $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>μ</mml:mi> </mml:math> is tightly bounded in this strong-field fields, placing meaningful limits on models predicting couplings between fundamental constants and gravity.