77 research outputs found
Vector chiral and multipolar orders in the spin-1/2 frustrated ferromagnetic chain in magnetic field
We study the one-dimensional spin-1/2 Heisenberg chain with competing
ferromagnetic nearest-neighbor J_1 and antiferromagnetic next-nearest-neighbor
J_2 exchange couplings in the presence of magnetic field. We use both numerical
approaches (the density matrix renormalization group method and exact
diagonalization) and effective field-theory approach, and obtain the
ground-state phase diagram for wide parameter range of the coupling ratio
J_1/J_2. The phase diagram is rich and has a variety of phases, including the
vector chiral phase, the nematic phase, and other multipolar phases. In the
vector chiral phase, which appears in relatively weak magnetic field, the
ground state exhibits long-range order (LRO) of vector chirality which
spontaneously breaks a parity symmetry. The nematic phase shows a quasi-LRO of
antiferro-nematic spin correlation, and arises as a result of formation of
two-magnon bound states in high magnetic fields. Similarly, the higher
multipolar phases, such as triatic (p=3) and quartic (p=4) phases, are formed
through binding of p magnons near the saturation fields, showing quasi-LRO of
antiferro-multipolar spin correlations. The multipolar phases cross over to
spin density wave phases as the magnetic field is decreased, before
encountering a phase transition to the vector chiral phase at a lower field.
The implications of our results to quasi-one-dimensional frustrated magnets
(e.g., LiCuVO_4) are discussed.Comment: v1. 20 pages, 18 figures: v2: 21 pages, 19 figures, Title modified
slightly. Some references, Fig.16, and a note are added. To appear in Phys.
Rev.
Reckoning with the Mother of all non-Fermi liquids: alien bosonization vs predator holography
This note addresses the problem of computing fermion propagators in a broad
variety of strongly correlated systems that can be mapped onto the theory of
fermions coupled to an (over)damped bosonic mode. A number of the previously
applied approaches and their results are reviewed, including the conventional
diagrammatic resummation and eikonal technique, as well as the 'experimental'
higher dimensional bosonization and generalized (i.e., 'bottom-up' or
'non-AdS/non-CFT') holographic conjecture. It appears that, by and large, those
results remain either in conflict or incomplete, thereby suggesting that the
ultimate solution to this ubiquitous problem is yet to be found.Comment: Latex, 12 pages, few typos correcte
Contrasting SYK-like Models
We contrast some aspects of various SYK-like models with large- melonic
behavior. First, we note that ungauged tensor models can exhibit symmetry
breaking, even though these are 0+1 dimensional theories. Related to this, we
show that when gauged, some of them admit no singlets, and are anomalous. The
uncolored Majorana tensor model with even is a simple case where gauge
singlets can exist in the spectrum. We outline a strategy for solving for the
singlet spectrum, taking advantage of the results in arXiv:1706.05364, and
reproduce the singlet states expected in . In the second part of the
paper, we contrast the random matrix aspects of some ungauged tensor models,
the original SYK model, and a model due to Gross and Rosenhaus. The latter,
even though disorder averaged, shows parallels with the Gurau-Witten model. In
particular, the two models fall into identical Andreev ensembles as a function
of . In an appendix, we contrast the (expected) spectra of AdS quantum
gravity, SYK and SYK-like tensor models, and the zeros of the Riemann Zeta
function.Comment: 45 pages, 17 figures; v2: minor improvements and rearrangements, refs
adde
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