Lattice Seminar

# Rotated twisted-mass: a convenient regularization scheme for isospin breaking QCD and QED lattice calculations

## by Dr Giuseppe Gagliardi (Università degli studi di Roma Tre)

Europe/Berlin
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Description

The evaluation of isospin breaking effects in hadronic observables has become an important goal of Lattice QCD and QED calculations in flavor physics. One of the common approaches to evaluate such effects through Lattice simulations is the so-called RM123 method, in which the path-integral is expanded around the isospin symmetric point in powers of the small parameters $\alpha_{em} \sim (m_{d}-m_{u})/\Lambda_{QCD} \sim \mathcal{O}(10^{-2})$. However, evaluating the quark-line disconnected contributions that appear in the RM123 expansion of several observables of interest is challenging, as in many cases they are found to be affected by large statistical fluctuations. In this talk, I will discuss a new scheme for twisted-mass
regularization of lattice QCD, the rotated twisted-mass (RTM) scheme, tailored to reduce, compared to standard twisted mass QCD, the statistical noise on some disconnected diagrams. Two numerical applications will be presented: the evaluation of the charged/neutral pion mass difference at order $\mathcal{O}(\alpha_{em})$, and the determination of the $\rm{SU}(2)$ chiral perturbation theory low-energy constant $\ell_{7}$.