##
The Mermin-Wagner theorem and quantum criticality in physical quasi-1d systems

Peter Richard Crompton **Hamburg University**
__Abstract:__

We identify the leading corrections to Finite-Size Scaling relations for the
Correlation length and Twist Order parameter of three mixed-spin chain systems
via QMC analysis, arguing that our results imply these systems can be described
by the same underlying conformal picture in correspondence with
recent pictures of deconfined quantum criticality at the vacuum angle,
$\theta=\pi$, both in zero and finite temperature quantum spin chains.
We propose a new effective theory for the critical region of quantum fluctuation
driven transitions and derive a renormalization group equation, suitable for
numerical evaluation via Quantum Monte Carlo analysis, that rigorously defines
the mapping between critical features in zero temperature and finite temperature
chains. We comment on the Mermin-Wagner theorem, and its rotational symmetry
breaking extensions, in this context.