New physics with the lepton flavor violating decay <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>τ</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mn>3</mml:mn><mml:mi>μ</mml:mi></mml:mrow></mml:math>
Physical review. D/Physical review. D.