A
bstract
We study the thermoelectric DC conductivities of Horndeski holographic models with momentum dissipation. We compute the butterfly velocity
v
B
and we discuss the existence of universal ...bounds on charge and energy diffusivities in the incoherent limit related to quantum chaos. We find that the Horndeski coupling represents a subleading contribution to the thermoelectric conductivities in the incoherent limit and therefore it does not affect any of the proposed bounds.
A
bstract
The chase of universal bounds on diffusivities in strongly coupled systems and holographic models has a long track record. The identification of a universal velocity scale, independent of ...the presence of well-defined quasiparticle excitations, is one of the major challenges of this program. A recent analysis, valid for emergent IR fixed points exhibiting local quantum criticality, and dual to IR AdS
2
geometries, suggests to identify such a velocity using the time and length scales at which hydrodynamics breaks down — the equilibration velocity. The latter relates to the radius of convergence of the hydrodynamic expansion and it is extracted from a collision between a hydrodynamic diffusive mode and a non-hydrodynamic mode associated to the IR AdS
2
region. In this short note, we confirm this picture for holographic systems displaying the spontaneous breaking of translational invariance. Moreover, we find that, at zero temperature, the lower bound set by quantum chaos and the upper one defined by causality and hydrodynamics exactly coincide, determining uniquely the diffusion constant. Finally, we comment on the meaning and universality of this newly proposed prescription.
It has been shown that holographic massive gravities can effectively realize spontaneous breaking of translational symmetry in homogenous manners. In this work, we consider a toy model of such ...category by adding a special gauge-axion coupling to the bulk action. Firstly, we identify the existence of spontaneous breaking of translations by the analysis on the UV expansion. In the absence of explicit breaking, the black hole solution is simply the same as the Reissner-Nodström(RN) black holes, regardless of the non-trivial profile of the bulk axions. The associated Goldstone modes exist only when the charge density is non-zero. Then, we investigate the optical conductivity both analytically as well as numercially. Our result perfectly agrees with that for a clean system, while the incoherent conductivity gets modified due to the symmetry breaking. The transverse Goldstone modes are dispersionless since the solution is dual to a
liquid
state. Finally, the effect of momentum relaxation to the transverse modes is considered. In this case, the would-be massless modes are pinned at certain frequency, which is another key difference from the unbroken states.
A
bstract
In this paper, we show that a simple generalization of the holographic axion model can realize spontaneous breaking of translational symmetry by considering a special gauge-axion higher ...derivative term. The finite real part and imaginary part of the stress tensor imply that the dual boundary system is a viscoelastic solid. By calculating quasi-normal modes and making a comparison with predictions from the elasticity theory, we verify the existence of phonons and pseudo-phonons, where the latter is realized by introducing a weak explicit breaking of translational symmetry, in the transverse channel. Finally, we discuss how the phonon dynamics affects the charge transport.
A
bstract
Using holographic methods in the Einstein-Maxwell-dilaton-axion (EMDA) theory, it was conjectured that the thermal diffusion in a strongly coupled metal without quasi-particles saturates an ...universal lower bound that is associated with the chaotic property of the system at infrared (IR) fixed points
1
. In this paper, we investigate the thermal transport and quantum chaos in the EMDA theory with a small Weyl coupling term. It is found that the Weyl coupling correct the thermal diffusion constant
D
Q
and butterfly velocity
v
B
in different ways, hence resulting in a modified relation between the two at IR fixed points. Unlike that in the EMDA case, our results show that the ratio
D
Q
/(
v
B
2
τ
L
) always contains a
non-universal
Weyl correction which depends also on the bulk fields as long as the U(1) current is marginally relevant in the IR.
A
bstract
Transport in strongly-disordered, metallic systems is governed by diffusive processes. Based on quantum mechanics, it has been conjectured that these diffusivities obey a lower bound
D/v
2
...≳ ℏ
/k
B
T
, the saturation of which provides a mechanism for the T-linear resistivity of bad metals. This bound features a characteristic velocity
v
, which was later argued to be the butterfly velocity
v
B
, based on holographic models of transport. This establishes a link between incoherent metallic transport, quantum chaos and Planckian timescales. Here we study higher derivative corrections to an effective holographic action of homogeneous disorder. The higher derivative terms involve only the charge and translation symmetry breaking sector. We show that they have a strong impact on the bound on charge diffusion
D
c
/
ν
B
2
≳
ℏ
/
k
B
T
, by potentially making the coefficient of its right-hand side arbitrarily small. On the other hand, the bound on energy diffusion is not affected.
Traditional Chinese medicine treatment of diseases has been recognized, but the material basis and mechanisms are not clear. In this study, target prediction of the antigastric cancer (GC) effect of ...Guiqi Baizhu (GQBZP) and the analysis of potential key compounds, key targets, and key pathways for the therapeutic effects against GC were carried out based on the method of network analysis and Kyoto Encyclopedia of Genes and Genomes enrichment. There were 33 proteins shared between GQBZP and GC, and 131 compounds of GQBZP had a high correlation with these proteins, indicating that the PI3K‐AKT signaling pathway might play a key role in GC. From these studies, we selected human epidermal growth factor receptor 2 (HER2) and programmed cell death 1‐ligand 1 (PD‐L1) for docking; the results showed that 385 and 189 compounds had high docking scores with HER2 and PD‐L1, respectively. Six compounds were selected for microscale thermophoresis (MST). Daidzein/quercetin and isorhamnetin/formononetin had the highest binding affinity for HER2 and PD‐L1, with Kd values of 3.7 μmol/L and 490, 667, and 355 nmol/L, respectively. Molecular dynamics simulation studies based on the docking complex structures as the initial conformation yielded the binding free energy between daidzein/quercetin with HER2 and isorhamnetin/formononetin with PD‐L1, calculated by molecular mechanics Poisson‐Boltzmann surface area, of −26.55, −14.18, −19.41, and −11.86 kcal/mol, respectively, and were consistent with the MST results. In vitro experiments showed that quercetin, daidzein, and isorhamnetin had potential antiproliferative effects in MKN‐45 cells. Enzyme activity assays showed that quercetin could inhibit the activity of HER2 with an IC50 of 570.07 nmol/L. Our study provides a systematic investigation to explain the material basis and molecular mechanism of traditional Chinese medicine in treating diseases.
We are committed to establishing a systematic research method based on network pharmacology, multitarget molecular docking, molecular dynamics simulation, and protein and experimental verification in vitro and in vivo, to establish a systematic analysis method for traditional Chinese medicine (TCM) treatment of diseases. We aim to provide a possible theoretical and experimental basis for the standardization and internationalization of TCM.
A
bstract
We study the linear stability of holographic homogeneous solids (HHS) at finite temperature and in presence of a background shear strain by means of a large scale quasi-normal mode analysis ...which extends beyond the hydrodynamic limit. We find that mechanical instability can arise either as a result of a complex speed of sound — gradient instability — or of a negative diffusion constant. Surprisingly, the simplest HHS models are linearly stable for arbitrarily large values of the background strain. For more complex HHS, the onset of the diffusive instability always precedes that of the gradient instability, which becomes the dominant destabilizing process only above a critical value of the background shear strain. Finally, we observe that the critical strains for the two instabilities approach each other at low temperatures. We conclude by presenting a phase diagram for HHS as a function of temperature and background shear strain which shows interesting similarities with the physics of superfluids in presence of background superfluid velocity.
We study the presence of universal bounds on transport in homogeneous
holographic models with broken translations. We verify numerically that,
in holographic systems with momentum dissipation, the ...viscosity to
entropy bound might be violated but the shear diffusion constant remains
bounded by below. This confirms the idea that
\eta/s
η
/
s
loses its privileged role in non-relativistic systems and that, in order
to find more universal bounds, one should rather look at diffusion
constants. We strengthen this idea by showing that, in presence of
spontaneously broken translations, the Goldstone diffusion constant
satisfies a universal lower bound in terms of the Planckian relaxation
time and the butterfly velocity. Additionally, all the diffusive
processes in the model satisfy an upper bound, imposed by causality,
which is given in terms of the thermalization time – the imaginary part
of the first non-hydrodynamic mode in the spectrum – and the speed of
longitudinal sound. Finally, we discuss the existence of a bound on the
speed of sound in holographic conformal solids and we show that the
conformal value acts as a lower (and not upper) bound on the speed of
longitudinal phonons. Nevertheless, we show that the stiffness
\partial p/\partial \epsilon
∂
p
/
∂
ϵ
is still bounded by above by its conformal value. This suggests that the
bounds conjectured in the past have to be considered on the stiffness of
the system, related to its equation of state, and not on the propagation
speed of sound.
A
bstract
We study a relation between the thermal diffusivity (
D
T
) and two quantum chaotic properties, Lyapunov time (τ
L
) and butterfly velocity (
v
B
) in strongly correlated systems by using a ...holographic method. Recently, it was shown that
E
i
:
=
D
T
,
i
/
v
B
,
i
2
τ
L
i
=
x
,
y
is universal in the sense that it is determined only by some scaling exponents of the IR metric in the low temperature limit regardless of the matter fields and ultraviolet data. Inspired by this observation, by analyzing the anisotropic IR scaling geometry carefully, we find the concrete expressions for
E
i
in terms of the critical dynamical exponents
z
i
in each direction,
E
i
=
z
i
/
2
z
i
−
1
. Furthermore, we find the lower bound of
E
i
is always 1
/
2, which is not affected by anisotropy, contrary to the
η/s
case. However, there may be an upper bound determined by given fixed anisotropy.
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