151 research outputs found
A Complexity for Quantum Field Theory States and Application in Thermofield Double States
This paper defines a complexity between states in quantum field theory by
introducing a Finsler structure based on ladder operators (the generalization
of creation and annihilation operators). Two simple models are shown as
examples to clarify the differences between complexity and other conceptions
such as complexity of formation and entanglement entropy. When it is applied
into thermofield double (TFD) states in -dimensional conformal field theory,
results show that the complexity density between them and corresponding vacuum
states are finite and proportional to , where is the temperature
of TFD state. Especially, a proof is given to show that fidelity susceptibility
of a TFD state is equivalent to the complexity between it and corresponding
vacuum state, which gives an explanation why they may share the same object in
holographic duality. Some enlightenments to holographic conjectures of
complexity are also discussed.Comment: Improved the language and presentation, adjusted the structure of the
paper, modified some errors and typos, added some appendices to give out more
detail
Multiple critical gravitational collapse of charged scalar with reflecting wall
In this paper, we present the results on the gravitational collapse of
charged massless scalar field in asymptotically flat spacetime with a perfectly
reflecting wall. Differing from previous works, we study the system in the
double null coordinates, by which we could simulate the system until the black
hole forms with higher precision but less performance time. We investigate the
influence of charge on the black hole formation and the scaling behavior near
the critical collapses. The gapless and gapped critical behaviors for black
hole mass and charge are studied numerically. We find that they satisfy the
scaling laws for critical gravitational collapse but the gapped critical
behavior is different from its AdS counterpart.Comment: 12 pages,8 figure
Coexistence and competition of ferromagnetism and p-wave superconductivity in holographic model
By combining a holographic p-wave superconductor model and a holographic
ferromagnetism model, we study the coexistence and competition of
ferromagnetism and p-wave superconductivity. It is found that the results
depend on the self-interaction of magnetic moment of the complex vector field
and which phase appears first. In the case that the ferromagnetic phase appears
first, if the interaction is attractive, the system shows the ferromagnetism
and superconductivity can coexist in low temperatures. If the interaction is
repulsive, the system will only be in a pure ferromagnetic state. In the case
that the superconducting phase appears first, the attractive interaction will
leads to a magnetic p-wave superconducting phase in low temperatures. If the
interaction is repulsive, the system will be in a pure p-wave superconducting
phase or ferromagnetic phase when the temperature is lowered.Comment: improved version, added some references and background knowledge
Comments on Joint Terms in Gravitational Action
This paper compares three different methods about computing joint terms in
on-shell action of gravity, which are identifying the joint term by the
variational principle in Dirichlet boundary condition, treating the joint term
as the limit contribution of smooth boundary and finding the joint term by
local SO(1,) transformation. In general metric gravitational theory, we
show that the differences between these joint terms are some variational
invariants under fixed boundary condition. We also give an explicit condition
to judge the existence of joint term determined by variational principle and
apply it into general relativity as an example.Comment: Published version with little modifications compared with previous
on
A Holographic Model for Paramagnetism/antiferromagnetism Phase Transition
In this paper we build a holographic model of
paramagnetism/antiferromagnetism phase transition, which is realized by
introducing two real antisymmetric tensor fields coupling to the background
gauge field strength and interacting with each other in a dyonic black brane
background. In the case without external magnetic field and in low
temperatures, the magnetic moments condense spontaneously in antiparallel
manner with the same magnitude and the time reversal symmetry is also broken
spontaneously (if boundary spatial dimension is more than 2, spatial rotational
symmetry is broken spontaneously as well), which leads to an antiferromagnetic
phase. In the case with weak external magnetic field, the magnetic
susceptibility density has a peak at the critical temperature and satisfies the
Curie-Weiss law in the paramagnetic phase of antiferromagnetism. In the strong
external magnetic field case, there is a critical magnetic field in
antiferromagnetic phase: when magnetic field reaches , the system will
return into the paramagnetic phase by a second order phase transition.Comment: The version published in PR
Understanding strongly coupling magnetism from holographic duality
The unusual magnetic materials are significant in both science and
technology. However, because of the strongly correlated effects, it is
difficult to understand their novel properties from theoretical aspects.
Holographic duality offers a new approach to understanding such systems from
gravity side. This paper will give a brief review of our recent works on the
applications of holographic duality in understanding unusual magnetic
materials. Some quantitative compare between holographic results and
experimental data will be shown and some predictions from holographic duality
models will be discussed.Comment: For Second LeCosPA Symposium at Taiwan National University, Taipai,
Dec. 14-18, 201
Insulator/metal phase transition and colossal magnetoresistance in holographic model
Within massive gravity, we construct a gravity dual for insulator/metal phase
transition and colossal magnetoresistance (CMR) effect found in some manganese
oxides materials. In heavy graviton limit, a remarkable
magnetic-field-sensitive DC resistivity peak appears at the Curie temperature,
where an insulator/metal phase transition happens and the magnetoresistance is
scaled with the square of field-induced magnetization. We find that metallic
and insulating phases coexist below the Curie point and the relation with the
electronic phase separation is discussed.Comment: Use massive gravity and consider reaction on the geometr
Scaling Laws in Gravitational Collapse
This paper presents two interesting scaling laws, which relate some critical
exponents in the critical behavior of spherically symmetric gravitational
collapses. These scaling laws are independent of the details of gravity theory
under consideration and share similar forms as those in thermodynamic and
geometrical phase transitions in condensed matter system. The properties of the
scaling laws are discussed and some numerical checks are given.Comment: 5 pages, 1 figur
Paramagnetism-Ferromagnetism Phase Transition in a Dyonic Black Hole
Coupling an antisymmetric tensor field to the electromagnetic field in a
dyonic Reissner-Nordstr\"om-AdS black hole background, we build a holographic
model for the paramagnetism/ferromagnetism phase transition. In the case of
zero magnetic field, the time reversal symmetry is broken spontaneously and
spontaneous magnetization happens in low temperature. The critical exponents
are in agreement with the ones from mean field theory. In the case of nonzero
magnetic field, the model realizes the hysteresis loop of single magnetic
domain and the magnetic susceptibility satisfies the Curie-Weiss law.Comment: To appear in PRD as a rapid communicatio
Gravity dualities of quantum distances
By choosing modular ground state as the reference state, this paper finds
that three most frequently-used distances and a quantum quasi-distance, i.e.
the trace distance, Fubini-Study distance, Bures distance and R\'{e}nyi
relative entropy, all have gravity dualities. Their gravity dualities have two
equivalent descriptions: one is given by the integration of the area of a
cosmic brane, the other one is given by the Euclidian on-shell action of dual
theory and the area of the cosmic brane. It then applies these dualities into
the 2-dimensional conformal field theory as examples and finds the results
match with the computations of field theory exactly.Comment: 1 figure, 11 page
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