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Abstract
A detailed investigation of finite size effects is performed for SU(2) gauge theory with two fermions in the adjoint representation, which previous lattice studies have shown to be inside the conformal window. The system is investigated with different spatial and temporal boundary conditions on lattices of various spatial and temporal extensions, for two values of the bare fermion mass representing a {\em heavy} and {\em light} fermion regime. Our study shows that the infinite volume limit of masses and decay constants in the mesonic sector is reached only when the mass of the pseudoscalar particle $M_\mathrm{PS}$ and the spatial lattice size $L$ satisfy the relation $L M_\mathrm{PS} \ge 15$. This bound, which is at least a factor of three higher than what observed in QCD, is a likely consequence of the different spectral signatures of the two theories, with the scalar isosinglet ($0^{++}$ glueball) being the lightest particle in our model. In addition to stressing the importance of simulating large lattice sizes, our analysis emphasises the need to understand quantitatively the {\em full} spectrum of the theory rather than just the spectrum in the mesonic isotriplet sector. While for the lightest fermion measuring masses from gluonic operators proves to be still challenging, reliable results for glueball states are obtained at the largest fermion mass and, in the mesonic sector, for both fermion masses. As a byproduct of our investigation, we perform a finite size scaling of the pseudoscalar mass and decay constant. The data presented in this work support the conformal behaviour of this theory with an anomalous dimension $\gamma_* \simeq 0.37$.
Original language  English 

Journal  Physical Review D  Particles, Fields, Gravitation and Cosmology 
Volume  93 
DOIs  
Publication status  Published  11 Mar 2016 
Keywords
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Dive into the research topics of 'Large volumes and spectroscopy of walking theories'. Together they form a unique fingerprint.Projects
 2 Finished

Highperformance computing at the highenergy frontier: results for the LHC
1/01/15 → 31/12/19
Project: Research

Particle Theory at the Higgs Centre
Ball, R., Berera, A., Boyle, P., CallisonBurch, C., Del Debbio, L., Gardi, E., Kennedy, A., O'Connell, D., Zwicky, R., Berera, A., Boyle, P., Buckley, A., Del Debbio, L., Gardi, E., Horsley, R., Kennedy, A., Kenway, R., O'Connell, D., Smillie, J. & Zwicky, R.
1/10/14 → 30/09/18
Project: Research
Profiles

Luigi Del Debbio
 School of Physics and Astronomy  Personal Chair in Theoretical High Energy Physics
Person: Academic: Research Active