Singlet channel scattering in a composite Higgs model on the lattice

<jats:title>Abstract</jats:title><jats:p>We present the first calculation of the scattering amplitude in the singlet channel beyond QCD. The calculation is performed in <jats:italic>SU</jats:italic>(2) gauge theory with <jats:inline-formula><jats:alternatives><jats:tex-math>$$N_f=2$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>N</mml:mi> <mml:mi>f</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> fundamental Dirac fermions and based on a finite-volume scattering formalism. The theory exhibits a <jats:inline-formula><jats:alternatives><jats:tex-math>$$SU(4) \rightarrow Sp(4)$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>S</mml:mi> <mml:mi>U</mml:mi> <mml:mo>(</mml:mo> <mml:mn>4</mml:mn> <mml:mo>)</mml:mo> <mml:mo>→</mml:mo> <mml:mi>S</mml:mi> <mml:mi>p</mml:mi> <mml:mo>(</mml:mo> <mml:mn>4</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> chiral symmetry breaking pattern that is used to design minimal composite Higgs models currently tested at the LHC. Our results show that, for the range of underlying fermion mass considered, the lowest flavour singlet state is stable.</jats:p>