272,915 research outputs found
Fragility of the Free-Energy Landscape of a Directed Polymer in Random Media
We examine the sensitiveness of the free-energy landscape of a directed
polymer in random media with respect to various kinds of infinitesimally weak
perturbation including the intriguing case of temperature-chaos. To this end,
we combine the replica Bethe ansatz approach outlined in cond-mat/0112384, the
mapping to a modified Sinai model and numerically exact calculations by the
transfer-matrix method. Our results imply that for all the perturbations under
study there is a slow crossover from a weakly perturbed regime where rare
events take place to a strongly perturbed regime at larger length scales beyond
the so called overlap length where typical events take place leading to chaos,
i.e. a complete reshuffling of the free-energy landscape. Within the replica
space, the evidence for chaos is found in the factorization of the replicated
partition function induced by infinitesimal perturbations. This is the reflex
of explicit replica symmetry breaking.Comment: 29 pages, Revtex4, ps figure
A New Solution to the Plasma Starved Event Horizon Magnetosphere: Application to the Forked Jet in M87
© 2018 ESO. Reproduced with permission from Astronomy & Astrophysics. Content in the UH Research Archive is made available for personal research, educational, and non-commercial purposes only. Unless otherwise stated, all content is protected by copyright, and in the absence of an open license, permissions for further re-use should be sought from the publisher, the author, or other copyright holder.Very Long Baseline Interferometry observations at 86 GHz reveal an almost hollow jet in M87 with a forked morphology. The detailed analysis presented here indicates that the spectral luminosity of the central spine of the jet in M87 is a few percent of that of the surrounding hollow jet 200-400 μ as from the central black hole. Furthermore, recent jet models indicate that a hollow "tubular" jet can explain a wide range of plausible broadband spectra originating from jetted plasma located within ~30 μ as of the central black hole, including the 230 GHz correlated flux detected by the Event Horizon Telescope. Most importantly, these hollow jets from the inner accretion flow have an intrinsic power capable of energizing the global jet out to kiloparsec scales. Thus motivated, this paper considers new models of the event horizon magnetosphere (EHM) in low luminosity accretion systems. Contrary to some models, the spine is not an invisible powerful jet. It is an intrinsically weak jet. In the new EHM solution, the accreted poloidal magnetic flux is weak and the background photon field is weak. It is shown how this accretion scenario naturally results in the dissipation of the accreted poloidal magnetic flux in the EHM not the accumulation of poloidal flux required for a powerful jet. The new solution indicates less large scale poloidal magnetic flux (and jet power) in the EHM than in the surrounding accretion flow and cannot support significant EHM driven jets.Peer reviewe
Weak-coupling phase diagrams of bond-aligned and diagonal doped Hubbard ladders
We study, using a perturbative renormalization group technique, the phase
diagrams of bond-aligned and diagonal Hubbard ladders defined as sections of a
square lattice with nearest-neighbor and next-nearest-neighbor hopping. We find
that for not too large hole doping and small next-nearest-neighbor hopping the
bond-aligned systems exhibit a fully spin-gapped phase while the diagonal
systems remain gapless. Increasing the next-nearest-neighbor hopping typically
leads to a decrease of the gap in the bond-aligned ladders, and to a transition
into a gapped phase in the diagonal ladders. Embedding the ladders in an
antiferromagnetic environment can lead to a reduction in the extent of the
gapped phases. These findings suggest a relation between the orientation of
hole-rich stripes and superconductivity as observed in LSCO.Comment: Published version. The set of RG equations in the presence of
magnetization was corrected and two figures were replace
Spectral features of a many-body localized system weakly coupled to a heat bath
We study many-body-localized (MBL) systems that are weakly coupled to
thermalizing environments, focusing on the spectral functions of local
operators. We argue that these spectral functions carry signatures of
localization even away from the limit of perfectly isolated systems. We find
that, in the limit of vanishing coupling to a bath, MBL systems come in two
varieties, with either discrete or continuous local spectra. Both varieties of
MBL systems exhibit a "soft gap" at zero frequency in the spatially-averaged
spectral functions of local operators, which serves as a diagnostic for
localization. We estimate the degree to which coupling to a bath broadens these
spectral features, and find that characteristics of incipient localization
survive as long as the system-bath coupling is much weaker than the
characteristic energy scales of the system. Since perfect isolation is
impossible, we expect the ideas discussed in this paper to be relevant for all
experiments on many-body localization.Comment: Expanded discussion of multiple lengthscales and of properties as a
quantum memor
Adiabatic freezing of long-range quantum correlations in spin chains
We consider a process to create quasi long-range quantum discord between the
non-interacting end spins of a quantum spin chain, with the end spins weakly
coupled to the bulk of the chain. The process is not only capable of creating
long-range quantum correlation but the latter remains frozen, when certain weak
end-couplings are adiabatically varied below certain thresholds. We term this
phenomenon as adiabatic freezing of quantum correlation. We observe that the
freezing is robust to moderate thermal fluctuations and is intrinsically
related to the cooperative properties of the quantum spin chain. In particular,
we find that the energy gap of the system remains frozen for these adiabatic
variations, and moreover, considering the end spins as probes, we show that the
interval of freezing can detect the anisotropy transition in quantum XY spin
chains. Importantly, the adiabatic freezing of long-range quantum correlations
can be simulated with contemporary experimental techniques.Comment: Main text (6 pages, 6 figures) and Supplemental material (4 pages, 4
figures), REVTeX 4-
Intrinsic Coulomb blockade in multi-wall carbon nanotubes
Carbon nanotubes provide a new class of molecular wires that display new and
exciting mesoscopic transport properties. We provide a detailed theoretical
description for transport in multi-wall nanotubes, where both disorder and
strong interactions are important. The interplay of both aspects leads to a
particularly effective intrinsic Coulomb blockade for tunneling. The relation
to recent experiments is discussed.Comment: 13 pages, incl 2 figs, for: Special issue "Transport in Molecular
Wires" in Chemical Physics, ed. by P. Hanggi, M. Ratner, S. Yalirak
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