56 research outputs found
Solving the Complex Phase Problem in a QCD Related Model
We discuss an effective theory for QCD at finite chemical potential and
non-zero temperature, where QCD is reduced to its center degrees of freedom.
The effective action can be mapped to a flux representation, where the complex
phase problem is solved and the theory accessible to Monte Carlo techniques. In
this work, we use a generalized Prokof'ev-Svistunov worm algorithm to perform
the simulations and determine the phase diagram as a function of temperature,
quark mass and chemical potential. It turns out that the transition is
qualitatively as expected for QCD.Comment: 6 pages and 3 figures, proceedings for "Excited QCD", Les Houches,
France, 20 - 25 February, 201
Chebyshev expansion for Impurity Models using Matrix Product States
We improve a recently developed expansion technique for calculating real
frequency spectral functions of any one-dimensional model with short-range
interactions, by postprocessing computed Chebyshev moments with linear
prediction. This can be achieved at virtually no cost and, in sharp contrast to
existing methods based on the dampening of the moments, improves the spectral
resolution rather than lowering it. We validate the method for the exactly
solvable resonating level model and the single impurity Anderson model. It is
capable of resolving sharp Kondo resonances, as well as peaks within the
Hubbard bands when employed as an impurity solver for dynamical mean-field
theory (DMFT). Our method works at zero temperature and allows for arbitrary
discretization of the bath spectrum. It achieves similar precision as the
dynamical density matrix renormalization group (DDMRG), at lower cost. We also
propose an alternative expansion, of 1-exp(-tau H) instead of the usual H,
which opens the possibility of using established methods for the time evolution
of matrix product states to calculate spectral functions directly.Comment: 13 pages, 9 figure
Universal front propagation in the quantum Ising chain with domain-wall initial states
We study the melting of domain walls in the ferromagnetic phase of the transverse Ising chain, created by flipping the order-parameter spins along one-half of the chain. If the initial state is excited by a local operator in terms of Jordan-Wigner fermions, the resulting longitudinal magnetization profiles have a universal character. Namely, after proper rescalings, the profiles in the noncritical Ising chain become identical to those obtained for a critical free-fermion chain starting from a step-like initial state. The relation holds exactly in the entire ferromagnetic phase of the Ising chain and can even be extended to the zero-field XY model by a duality argument. In contrast, for domain-wall excitations that are highly non-local in the fermionic variables, the universality of the magnetization profiles is lost. Nevertheless, for both cases we observe that the entanglement entropy asymptotically saturates at the ground-state value, suggesting a simple form of the steady state
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