Sigma terms and strangeness content of the nucleon with $Nf=2+1+1$ twisted mass fermions

Understand

We investigate excited state contaminations in a direct computation of the nucleon $\sigma$-terms.

• This is an important source of systematic effects that needs to be controlled besides the light quark mass dependence and lattice artefacts.
• We use maximally twisted mass fermions with dynamical light ($u$,$d$), strange and charm degrees of freedom.
• Employing an efficient stochastic evaluation of the disconnected contribution available for twisted mass fermions, we show that the effect of excited states is large in particular for the strange $\sigma$-terms, where it can be as big as $O(\gtrsim 40%$).