18,870 research outputs found
More on complexity of operators in quantum field theory
Recently it has been shown that the complexity of SU() operator is
determined by the geodesic length in a bi-invariant Finsler geometry, which is
constrained by some symmetries of quantum field theory. It is based on three
axioms and one assumption regarding the complexity in continuous systems. By
relaxing one axiom and an assumption, we find that the complexity formula is
naturally generalized to the Schatten -norm type. We also clarify the
relation between our complexity and other works. First, we show that our
results in a bi-invariant geometry are consistent with the ones in a
right-invariant geometry such as -local geometry. Here, a careful analysis
of the sectional curvature is crucial. Second, we show that our complexity can
concretely realize the conjectured pattern of the time-evolution of the
complexity: the linear growth up to saturation time. The saturation time can be
estimated by the relation between the topology and curvature of SU() groups.Comment: Modified the Sec. 4.1, where we offered a powerful proof: if (1) the
ket vector and bra vector in quantum mechanics contain same physics, or (2)
adding divergent terms to a Lagrangian will not change underlying physics,
then complexity in quantum mechanics must be bi-invariant
Principles and symmetries of complexity in quantum field theory
Based on general and minimal properties of the {\it discrete} circuit
complexity, we define the complexity in {\it continuous} systems in a
geometrical way. We first show that the Finsler metric naturally emerges in the
geometry of the complexity in continuous systems. Due to fundamental symmetries
of quantum field theories, the Finsler metric is more constrained and
consequently, the complexity of SU() operators is uniquely determined as a
length of a geodesic in the Finsler geometry. Our Finsler metric is
bi-invariant contrary to the right-invariance of discrete qubit systems. We
clarify why the bi-invariance is relevant in quantum field theoretic systems.
After comparing our results with discrete qubit systems we show most results in
-local right-invariant metric can also appear in our framework. Based on the
bi-invariance of our formalism, we propose a new interpretation for the
Schr\"{o}dinger's equation in isolated systems - the quantum state evolves by
the process of minimizing "computational cost."Comment: Published version; added a short introduction on Finsler geometr
Electrical Control of Magnetization in Charge-ordered Multiferroic LuFe2O4
LuFe2O4 exhibits multiferroicity due to charge order on a frustrated
triangular lattice. We find that the magnetization of LuFe2O4 in the
multiferroic state can be electrically controlled by applying voltage pulses.
Depending on with or without magnetic fields, the magnetization can be
electrically switched up or down. We have excluded thermal heating effect and
attributed this electrical control of magnetization to an intrinsic
magnetoelectric coupling in response to the electrical breakdown of charge
ordering. Our findings open up a new route toward electrical control of
magnetization.Comment: 14 pages, 5 figure
Portfolio Optimization on Multivariate Regime Switching GARCH Model with Normal Tempered Stable Innovation
We propose a Markov regime switching GARCH model with multivariate normal
tempered stable innovation to accommodate fat tails and other stylized facts in
returns of financial assets. The model is used to simulate sample paths as
input for portfolio optimization with risk measures, namely, conditional value
at risk and conditional drawdown. The motivation is to have a portfolio that
avoids left tail events by combining models that incorporates fat tail with
optimization that focuses on tail risk. In-sample test is conducted to
demonstrate goodness of fit. Out-of-sample test shows that our approach yields
higher performance measured by Sharpe-like ratios than the market and equally
weighted portfolio in recent years which includes some of the most volatile
periods in history. We also find that suboptimal portfolios with higher return
constraints tend to outperform optimal portfolios
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Spatiomechanical Modulation of EphB4-Ephrin-B2 Signaling in Neural Stem Cell Differentiation.
Interactions between EphB4 receptor tyrosine kinases and their membrane-bound ephrin-B2 ligands on apposed cells play a regulatory role in neural stem cell differentiation. With both receptor and ligand constrained to move within the membranes of their respective cells, this signaling system inevitably experiences spatial confinement and mechanical forces in conjunction with receptor-ligand binding. In this study, we reconstitute the EphB4-ephrin-B2 juxtacrine signaling geometry using a supported-lipid-bilayer system presenting laterally mobile and monomeric ephrin-B2 ligands to live neural stem cells. This experimental platform successfully reconstitutes EphB4-ephrin-B2 binding, lateral clustering, downstream signaling activation, and neuronal differentiation, all in a configuration that preserves the spatiomechanical aspects of the natural juxtacrine signaling geometry. Additionally, the supported bilayer system allows control of lateral movement and clustering of the receptor-ligand complexes through patterns of physical barriers to lateral diffusion fabricated onto the underlying substrate. The results from this study reveal a distinct spatiomechanical effect on the ability of EphB4-ephrin-B2 signaling to induce neuronal differentiation. These observations parallel similar studies of the EphA2-ephrin-A1 system in a very different biological context, suggesting that such spatiomechanical regulation may be a common feature of Eph-ephrin signaling
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