Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The mass-flow error in the Numerical Renormalization Group method and
  the critical behavior of the sub-ohmic spin-boson model   We discuss a particular source of error in the Numerical Renormalization
Group (NRG) method for quantum impurity problems, which is related to a
renormalization of impurity parameters due to the bath propagator. At any step
of the NRG calculation, this renormalization is only partially taken into
account, leading to systematic variation of the impurity parameters along the
flow. This effect can cause qualitatively incorrect results when studying
quantum critical phenomena, as it leads to an implicit variation of the phase
transition's control parameter as function of the temperature and thus to an
unphysical temperature dependence of the order-parameter mass. We demonstrate
the mass-flow effect for bosonic impurity models with a power law bath
spectrum, J(w) ~ w^s, namely the dissipative harmonic oscillator and the
spin-boson model. We propose an extension of the NRG to correct the mass-flow
error. Using this, we find unambiguous signatures of a Gaussian critical fixed
point in the spin-boson model for s<1/2, consistent with mean-field behavior as
expected from quantum-to-classical mapping.

37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
11
The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
6
The categories of this paper are: astro-ph
17
The categories of this paper are: q-fin