674 research outputs found
Deconfined quantum criticality in spin-1/2 chains with long-range interactions
We study spin-1/2 chains with long-range power-law decaying unfrustrated (bipartite) Heisenberg exchange J_r ∝ r^- and multi-spin interactions Q favoring a valence-bond solid (VBS) ground state. Employing quantum Monte Carlo techniques and Lanczos diagonalization, we analyze order parameters and excited-state level crossings to characterize quantum states and phase transitions in the (,Q) plane. For weak Q and sufficiently slowly decaying Heisenberg interactions (small ), the system has a long-range-ordered antiferromagnetic (AFM) ground state, and upon increasing there is a continuous transition into a quasi long-range ordered (QLRO) critical state of the type in the standard Heisenberg chain. For rapidly decaying long-range interactions, there is transition between QLRO and VBS ground states of the same kind as in the frustrated J_1-J_2 Heisenberg chain. Our most important finding is a direct continuous quantum phase transition between the AFM and VBS states - a close analogy to the 2D deconfined quantum-critical point. In previous 1D analogies the ordered phases both have gapped fractional excitations, and the critical point is a conventional Luttinger-Liquid. In our model the excitations fractionalize upon transitioning from the AFM state, changing from spin waves to deconfined spinons. We extract critical exponents at the AFM-VBS transition and use order-parameter distributions to study emergent symmetries. We find emergent O(4) symmetry of the O(3) AFM and scalar VBS order parameters. Thus, the order parameter fluctuations exhibit the covariance of a uniaxially deformed O(4) sphere (an "elliptical" symmetry). This unusual quantum phase transition does not yet have any known field theory description, and our detailed results can serve to guide its construction. We discuss possible experimental realizations.First author draf
Quasinormal modes for asymptotic safe black holes
Under the hypothesis of asymptotic safety of gravity, the static, spherically
symmetric black hole solutions in the infrared limit are corrected by
non-perturbative effects. Specifically, the metric is modified by the running
of gravitational couplings. In this work, we investigate the effects of this
correction to the quasinormal modes (QNMs) of a test scalar field propagating
in this kind of black hole background analytically and numerically. It is found
that although the quasi-period frequencies and the damping of oscillations are
respectively enhanced and weakened by the quantum correction term, the
stability of the black hole remains.Comment: 11 pages, 1 figures, accepted for publication in CQG. arXiv admin
note: text overlap with arXiv:1007.131
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