Quantum Origins of the Density Operator. (arXiv:2104.07465v1 [physics.gen-ph])
| 上午10:31 | | | Mark G. Kuzyk | | | quant-ph updates on arXiv.org |
Students in quantum mechanics class are taught that the wave function contains all knowable information about an isolated system. Later in the course, this view seems to be contradicted by the mysterious density matrix, which introduces a new set of probabilities in addition to those that are built into the wave function. This paper brings attention to the fact that the density matrix can be reconciled with the underlying quantum-mechanical description using a two-particle entangled state with a one-particle subsystem as the simplest illustration of the basic principle. The extra-quantum probabilities are traced to the coefficients of superposition of the quantum state vector and the seemingly irreversible exponential population decay is shown to be compatible with the unitary time evolution of a pure state when the two particles interact. The two-particle universe thus provides the student with a tool for understanding how the density operator, with all its richness, emerges from quantum mechanics.
Twistor action for general relativity. (arXiv:2104.07031v1 [hep-th])
| 上午10:31 | | | gr-qc updates on arXiv.org |
Authors: Atul Sharma
We reformulate Euclidean general relativity without cosmological constant as an action governing the complex structure of twistor space. Extending Penrose’s non-linear graviton construction, we find a correspondence between twistor spaces with partially integrable almost complex structures and four-dimensional space-times with off-shell metrics. Using this, we prove that our twistor action reduces to Plebanski’s action for general relativity via the Penrose transform. This should lead to new insights into the geometry of graviton scattering as well as to the derivation of computational tools like gravitational MHV rules.
| 上午10:31 | | | gr-qc updates on arXiv.org |
Authors: Brett McInnes
The Weak Gravity Conjecture requires that it be possible for all (classically stable) extremal black holes to decay. The “black hole version” of the conjecture requires that it should be possible for this to occur through the emission of smaller black holes. We consider this version in the case of extremal AdS$_4$-Kerr-Newman black holes which are stable against a superradiant instability. One finds that the emitted black hole must be very exotic, having a direction-dependent causal structure. This is independent of the question as to whether the emitted black hole necessarily violates classical Cosmic Censorship. When the system is embedded in string theory, however, we find that it (probably) does.
Born-Oppenheimer meets Wigner-Weyl in Quantum Gravity. (arXiv:2104.07480v1 [gr-qc])
| 上午10:31 | | | gr-qc updates on arXiv.org |
Authors: A. Y. Kamenshchik, A. Tronconi, G. Venturi
Starting from a Born-Oppenheimer decomposition of the Wheeler-DeWitt equation for the quantum cosmology of the matter-gravity system, we have performed a Wigner-Weyl transformation and obtained equations involving a Wigner function for the scale factor and its conjugate momentum. This has allowed us to study in more detail than previously the approach to the classical limit of gravitation and the way time emerges in such a limit. To lowest order we reproduce the Friedmann equation and the previously obtained equation for the evolution of matter. We also obtain expressions for higher order corrections to the semi-classical limit.
Losing the trace to find dynamical Newton or Planck constants. (arXiv:2011.07055v2 [gr-qc] UPDATED)
| 上午10:31 | | | gr-qc updates on arXiv.org |
Authors: Pavel Jiroušek, Keigo Shimada, Alexander Vikman, Masahide Yamaguchi
We show that promoting the trace part of the Einstein equations to a trivial identity results in the Newton constant being an integration constant. Thus, in this formulation the Newton constant is a global dynamical degree of freedom which is also a subject to quantization and quantum fluctuations. This is similar to what happens to the cosmological constant in the unimodular gravity where the trace part of the Einstein equations is lost in a different way. We introduce a constrained variational formulation of these modified Einstein equations. Then, drawing on analogies with the Henneaux-Teitelboim action for unimodular gravity, we construct different general-covariant actions resulting in these dynamics. The inverse of dynamical Newton constant is canonically conjugated to the Ricci scalar integrated over spacetime. Surprisingly, instead of the dynamical Newton constant one can formulate an equivalent theory with a dynamical Planck constant. Finally, we show that an axion-like field can play a role of the gravitational Newton constant or even of the quantum Planck constant.
Modified gravity: a unified approach. (arXiv:2103.15906v2 [gr-qc] UPDATED)
| 上午10:31 | | | gr-qc updates on arXiv.org |
Authors: Christian G. Boehmer, Erik Jensko
Starting from the original Einstein action, sometimes called the Gamma squared action, we propose a new setup to formulate modified theories of gravity. This can yield a theory with second order field equations similar to those found in other popular modified gravity models. Using a more general setting the theory gives fourth order equations. This model is based on the metric alone and does not require more general geometries. It is possible to show that our new theory and the recently proposed $f(Q)$ gravity models are equivalent at the level of the action and at the level of the field equations, provided that appropriate boundary terms are taken into account. Our theory can also match up with $f(R)$ gravity which is an expected result. Perhaps more surprisingly, we can also show that this equivalence extends to $f(T)$ gravity at the level of the action and its field equations, provided that appropriate boundary terms are taken in account. While these three theories are conceptually different and are based on different geometrical settings, we can establish the necessary conditions under which their field equations are indistinguishable. The final part requires matter to couple minimally to gravity. Through this work we emphasise the importance played by boundary terms which are at the heart of our approach.
| 上午10:31 | | | gr-qc updates on arXiv.org |
We focus on two types of coherent states, the coherent states of multi graviton states and the coherent states of giant graviton states, in the context of gauge/gravity correspondence. We conveniently use a phase shift operator and its actions on the superpositions of these coherent states. We find $N$-state Schrodinger cat states which approach the one-row Young tableau states, with fidelity between them asymptotically reaches 1 at large $N$. The quantum Fisher information of these states is proportional to the variance of the excitation energy of the underlying states, and characterizes the localizability of the states in the angular direction in the phase space. We analyze the correlation and entanglement between gravitational degrees of freedom using different regions of the phase space plane in bubbling AdS. The correlation between two entangled rings in the phase space plane is related to the area of the annulus between the two rings. We also analyze two types of noisy coherent states, which can be viewed as interpolated states that interpolate between a pure coherent state in the noiseless limit and a maximally mixed state in the large noise limit.
Scientific Conclusions Need Not Be Accurate, Justified, or Believed by their Authors
| 上午2:27 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Dang, Haixin and Bright, Liam Kofi (2021) Scientific Conclusions Need Not Be Accurate, Justified, or Believed by their Authors. [Preprint]
Numerical instability and dynamical systems
| 上午2:25 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Ardourel, Vincent and Jebeile, Julie (2021) Numerical instability and dynamical systems. [Preprint]
Geometric objects and perspectivalism
| 上午2:25 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Read, James (2021) Geometric objects and perspectivalism. [Preprint]
Tunnelling Times in Quantum Mechanics
| 上午2:23 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Puleston, James (2020) Tunnelling Times in Quantum Mechanics. UNSPECIFIED, Cambridge.
Localizable Particles in the Classical Limit of Quantum Field Theory
| 2021年4月14日 星期三 下午2:38 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Feintzeig, Benjamin and Librande, Jonah and Soiffer, Rory (2021) Localizable Particles in the Classical Limit of Quantum Field Theory. Foundations of Physics.
| 2021年4月14日 星期三 下午2:37 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Loewer, Barry (2021) Are Humean Laws Flukes? [Preprint]
Quantum superpositions and the measurement problem
| 2021年4月13日 星期二 下午2:09 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Henriksson, Andreas (2021) Quantum superpositions and the measurement problem. [Preprint]
Fidelity and mistaken identity for symplectic quantum states
| 2021年4月13日 星期二 下午2:08 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Henriksson, Andreas (2021) Fidelity and mistaken identity for symplectic quantum states. [Preprint]
| 2021年4月13日 星期二 上午8:00 | | | Latest Results for Synthese |
Abstract
Predictive processing theories are increasingly popular in philosophy of mind; such process theories often gain support from the Free Energy Principle (FEP)—a normative principle for adaptive self-organized systems. Yet there is a current and much discussed debate about conflicting philosophical interpretations of FEP, e.g., representational versus non-representational. Here we argue that these different interpretations depend on implicit assumptions about what qualifies (or fails to qualify) as representational. We deploy the Free Energy Principle (FEP) instrumentally to distinguish four main notions of representation, which focus on organizational, structural, content-related and functional aspects, respectively. The various ways that these different aspects matter in arriving at representational or non-representational interpretations of the Free Energy Principle are discussed. We also discuss how the Free Energy Principle may be seen as a unified view where terms that traditionally belong to different ontologies—e.g., notions of model and expectation versus notions of autopoiesis and synchronization—can be harmonized. However, rather than attempting to settle the representationalist versus non-representationalist debate and reveal something about what representations are simpliciter, this paper demonstrates how the Free Energy Principle may be used to reveal something about those partaking in the debate; namely, what our hidden assumptions about what representations are—assumptions that act as sometimes antithetical starting points in this persistent philosophical debate.
Necessitarianism and Dispositions
| 2021年4月12日 星期一 下午2:34 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Gozzano, Simone (2020) Necessitarianism and Dispositions. [Preprint]
Quantum Gravity and Mereology: Not So Simple
| 2021年4月12日 星期一 下午2:31 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Baron, Samuel and Le Bihan, Baptiste (2021) Quantum Gravity and Mereology: Not So Simple. [Preprint]
Measurement of the proton spin structure at long distances
| 2021年4月12日 星期一 上午8:00 | | | Z. W. Zhao | | | Nature Physics – Issue – nature.com science feeds |
Nature Physics, Published online: 12 April 2021; doi:10.1038/s41567-021-01198-z
Measurements of the proton’s spin structure in experiments scattering a polarized electron beam off polarized protons in regions of low momentum transfer squared test predictions from chiral effective field theory of the strong interaction.
Physicalism without the idols of mathematics
| 2021年4月12日 星期一 上午6:48 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |
Szabo, Laszlo E. (2021) Physicalism without the idols of mathematics. [Preprint]
