# Weekly Papers on Quantum Foundations (25)

A note on the inner products of pure states and their antidistinguishability. (arXiv:2206.08313v1 [quant-ph])

A set of d quantum states is said to be antidistinguishable if there exists a d-outcome POVM that can perfectly identify which state was not measured. A conjecture by Havl\’i\v{c}ek and Barrett states that if a set of d pure states has small pair-wise inner products, then the set must be antidistinguishable. In this note we provide a certificate of antidistinguishability via semidefinite programming duality and use it to provide a counterexample to this conjecture when d = 4.

Geometric Event-Based Relativistic Quantum Mechanics. (arXiv:2206.08359v1 [quant-ph])

We propose a special relativistic framework for quantum mechanics. It is based on introducing a Hilbert space for events. Events are taken as primitive notions (as customary in relativity), whereas quantum systems (e.g. fields and particles) are emergent in the form of joint probability amplitudes for position and time of events. Textbook relativistic quantum mechanics and quantum field theory can be recovered by dividing the event Hilbert spaces into space and time (a foliation) and then conditioning the event states onto the time part. Our theory satisfies the full Poincare’ symmetry as a geometric’ unitary transformation, and possesses observables for space (location of an event) and time (position in time of an event).

On efforts to decouple early universe cosmology and quantum gravity research. (arXiv:2206.07783v1 [physics.hist-ph])

Authors: Mike D. Schneider

The Big Bang singularity in standard model cosmology suggests a relationship between early universe cosmology and quantum gravity phenomenology. Inflation is usually thought to undermine that relationship by means of a dynamical diluting argument, but this argument has recently been disputed in the form of a ‘trans-Planckian censorship’ conjecture. Ijjas and Steinhardt [“Bouncing cosmology made simple”, “A new kind of cyclic universe”] implicitly advocate an alternative approach: ‘generalized cosmic censorship’. I contrast generalized cosmic censorship with the logic of its namesake: the cosmic censorship conjectures. I also remark on foundational concerns in the program of research beyond the standard model, which would be based on such a principle — a program I dub ‘cosmology done as effective field theory’, or the empirical study of an ‘effective cosmos’.

Quantum probability from causal structure. (arXiv:2112.10929v4 [quant-ph] UPDATED)

Authors: Michael Ridley

The Born probability measure describes the statistics of measurements in which observers self-locate themselves in some region of reality. In $\psi$-ontic quantum theories, reality is directly represented by the wavefunction. We show that quantum probabilities may be identified with fractions of a universal multiple-time wavefunction containing both causal and retrocausal temporal parts. This wavefunction is defined in an appropriately generalized history space on the Keldysh time contour. Our deterministic formulation of quantum mechanics replaces the initial condition of standard Schr\”odinger dynamics with a network of fixed points’ defining quantum histories on the contour. The Born measure is derived by summing up the wavefunction along these histories. We then apply the same technique to the derivation of the statistics of measurements with pre- and post-selection.

Quantum solitodynamics: Non-linear wave mechanics and pilot-wave theory. (arXiv:2205.04706v2 [quant-ph] UPDATED)

Authors: Aurélien Drezet

In 1927 Louis de Broglie proposed an alternative approach to standard quantum mechanics known as the double solution program (DSP) where particles are represented as bunched fields or solitons guided by a base (weaker) wave. DSP evolved as the famous de Broglie-Bohm pilot wave interpretation (PWI) also known as Bohmian mechanics but the general idea to use solitons guided by a base wave to reproduce the dynamics of the PWI was abandonned. Here we propose a nonlinear scalar field theory able to reproduce the PWI for the Schr\”{o}dinger and Klein-Gordon guiding waves. Our model relies on a relativistic `phase harmony’ condition locking the phases of the solitonic particle and the guiding wave. We also discuss an extension of the theory for the $N$ particles cases in presence of entanglement and external (classical) electromagnectic fields.

Quest for eternal oscillons. (arXiv:2206.07900v1 [gr-qc])

Authors: T. S. MendonçaH. P. de Oliveira

Nonlinear field theories produce unstable but long-lived configurations known as oscillons. These structures have been studied with asymmetric and symmetric double-well potentials and extended to other forms of potentials. In the present work, we examine the consequences of considering higher-order field theories, where we have used a generalization of the symmetric double-well potential and a $\phi^6$ potential. Consequently, we have found $3+1$ spherically symmetric oscillons with significantly large lifetimes without parameter fine-tuning.

Lorentz Symmetry Violation of Cosmic Photons. (arXiv:2206.08180v1 [astro-ph.HE])

Authors: Ping HeBo-Qiang Ma

As a basic symmetry of space-time, Lorentz symmetry has played important roles in various fields of physics, and it is a glamorous question whether Lorentz symmetry breaks. Since Einstein proposed special relativity, Lorentz symmetry has withstood very strict tests, but there are still motivations for Lorentz symmetry violation (LV) research from both theoretical consideration and experimental feasibility, that attract physicists to work on LV theories, phenomena and experimental tests with enthusiasm. There are many theoretical models including LV effects, and different theoretical models predict different LV phenomena, from which we can verify or constrain LV effects. Here, we introduce three types of LV theories: quantum gravity theory, space-time structure theory and effective field theory with extra-terms. Limited by the energy of particles, the experimental tests of LV are very difficult; however, due to the high energy and long propagation distance, high-energy particles from astronomical sources can be used for LV phenomenological researches. Especially with cosmic photons, various astronomical observations provide rich data from which one can obtain various constraints for LV researches. Here, we review four common astronomical phenomena which are ideal for LV studies, together with current constraints on LV effects of photons.

Thinking outside the box: Numerical Relativity with particles. (arXiv:2205.08130v2 [gr-qc] UPDATED)

Authors: S. RosswogP. DienerF. Torsello

To date, essentially all simulation codes that solve the full set of Einstein’s equations are performed in the framework of Eulerian hydrodynamics. The exception is our recently developed Numerical Relativity code SPHINCS_BSSN which solves the commonly used BSSN formulation of the Einstein equations on a structured mesh and the matter equations via Lagrangian particles. We show here, for the first time, SPHINCS_BSSN neutron star merger simulations with piecewise polytropic approximations to four nuclear matter equations of state. In this set of neutron star merger simulations we focus on perfectly symmetric binary systems that are irrotational and have 1.3 $M_\odot$ masses. We introduce some further methodological refinements (a new way of steering dissipation, an improved particle-mesh mapping) and we explore the impact of the exponent that enters in the calculation of the thermal pressure contribution. We find that it leaves a noticeable imprint on the gravitational wave amplitude (calculated via both quadrupole approximation and the $\Psi_4$-formalism) and has a noticeable impact on the amount of dynamic ejecta. Consistent with earlier findings, we only find a few times $10^{-3}$ \Msun as dynamic ejecta in the studied equal mass binary systems, with softer equations of state (which are more prone to shock formation) ejecting larger amounts of matter. In all of the cases, we see a credible high-velocity ($\sim0.5 .. 0.7c$) ejecta component of $\sim 10^{-4}$ \Msun that is launched at contact from the interface between the two neutron stars. Such a high-velocity component has been suggested to produce an early, blue precursor to the main kilonova emission and it could also potentially cause a kilonova afterglow.

The Epiphenomena Argument for Symmetry-to-Reality Inference

Baker, David John (2022) The Epiphenomena Argument for Symmetry-to-Reality Inference. In: UNSPECIFIED.

Free Energy: A User’s Guide

Mann, Stephen Francis and Pain, Ross and Kirchhoff, Michael (2022) Free Energy: A User’s Guide. Biology & Philosophy. ISSN 1572-8404

Modest Scientific Realism and Belief in Astronomical Entities

Allzén, Simon (2022) Modest Scientific Realism and Belief in Astronomical Entities. In: UNSPECIFIED.

T Falls Apart: On the Status of Classical Temperature in Relativity

Chua, Eugene (2022) T Falls Apart: On the Status of Classical Temperature in Relativity. In: UNSPECIFIED.

The Π-Theorem as a Guide to Quantity Symmetries and the Argument Against Absolutism

Jalloh, Mahmoud (2022) The Π-Theorem as a Guide to Quantity Symmetries and the Argument Against Absolutism. UNSPECIFIED.

A No-Go Theorem for psi-Ontic Models

Carcassi, Gabriele and Aidala, Christine A and Oldofredi, Andrea (2022) A No-Go Theorem for psi-Ontic Models. [Preprint]

Consciousness and Quantum Mechanics

Gao, Shan (2022) Consciousness and Quantum Mechanics. [Preprint]