Change search
Link to record
Permanent link

Direct link
Publications (8 of 8) Show all publications
Eberhardt, A., Zamora, A., Kopp, M. & Abel, T. (2024). Classical field approximation of ultralight dark matter: Quantum break times, corrections, and decoherence. Physical Review D: covering particles, fields, gravitation, and cosmology, 109(8), Article ID 083527.
Open this publication in new window or tab >>Classical field approximation of ultralight dark matter: Quantum break times, corrections, and decoherence
2024 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 109, no 8, article id 083527Article in journal (Refereed) Published
Abstract [en]

The classical field approximation is widely used to better understand the predictions of ultralight dark matter. Here, we use the truncated Wigner approximation method to test the classical field approximation of ultralight dark matter. This method approximates a quantum state as an ensemble of independently evolving realizations drawn from its Wigner function. The method is highly parallelizable and allows the direct simulation of quantum corrections and decoherence times in systems many times larger than have been previously studied in reference to ultralight dark matter. Our study involves simulation of systems in 1, 2, and 3 spatial dimensions. We simulate three systems, the condensation of a Gaussian random field in three spatial dimensions, a stable collapsed object in three spatial dimensions, and the merging of two stable objects in two spatial dimensions. We study the quantum corrections to the classical field theory in each case. We find that quantum corrections grow exponentially during nonlinear growth with the timescale being approximately equal to the system dynamical time. In stable systems the corrections grow quadratically. We also find that the primary effect of quantum corrections is to reduce the amplitude of fluctuations on the de Broglie scale in the spatial density. Finally, we find that the timescale associated with decoherence due to gravitational coupling to baryonic matter is at least as fast as the quantum corrections due to gravitational interactions. These results are consistent with the predictions of the classical field theory being accurate.

National Category
Subatomic Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-232238 (URN)10.1103/PhysRevD.109.083527 (DOI)001224283200003 ()2-s2.0-85191859662 (Scopus ID)
Available from: 2024-08-13 Created: 2024-08-13 Last updated: 2024-08-13Bibliographically approved
Kopp, M., Fragkos, V. & Pikovski, I. (2022). Nonclassicality of axionlike dark matter through gravitational self-interactions. Physical Review D: covering particles, fields, gravitation, and cosmology, 106(4), Article ID 043517.
Open this publication in new window or tab >>Nonclassicality of axionlike dark matter through gravitational self-interactions
2022 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 106, no 4, article id 043517Article in journal (Refereed) Published
Abstract [en]

Axionlike particles (ALPs) are promising dark matter candidates. They are typically described by a classical field, motivated by large phase space occupation numbers. Here we show that such a description is accompanied by a quantum effect: squeezing due to gravitational self-interactions. For a typical QCD axion today, the onset of squeezing is reached on μs scales and grows over millennia. Thus within the usual models based on the classical Schrödinger-Poisson equation, a type of Gross-Pitaevskii equation, any viable ALP is nonclassical. We also show that squeezing may be relevant on the scales of other self-gravitating systems such as galactic haloes, or solitonic cores. Conversely, our results highlight the incompleteness and limitations of the classical single field description of ALPs.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-210620 (URN)10.1103/PhysRevD.106.043517 (DOI)000861136200012 ()2-s2.0-85136098867 (Scopus ID)
Available from: 2022-10-26 Created: 2022-10-26 Last updated: 2025-02-05Bibliographically approved
Fragkos, V., Kopp, M. & Pikovski, I. (2022). On inference of quantization from gravitationally induced entanglement. AVS Quantum science, 4(4), Article ID 045601.
Open this publication in new window or tab >>On inference of quantization from gravitationally induced entanglement
2022 (English)In: AVS Quantum science, E-ISSN 2639-0213, Vol. 4, no 4, article id 045601Article in journal (Refereed) Published
Abstract [en]

Observable signatures of the quantum nature of gravity at low energies have recently emerged as a promising new research field. One prominent avenue is to test for gravitationally induced entanglement between two mesoscopic masses prepared in spatial superposition. Here, we analyze such proposals and what one can infer from them about the quantum nature of gravity as well as the electromagnetic analogues of such tests. We show that it is not possible to draw conclusions about mediators: even within relativistic physics, entanglement generation can equally be described in terms of mediators or in terms of non-local processes—relativity does not dictate a local channel. Such indirect tests, therefore, have limited ability to probe the nature of the process establishing the entanglement as their interpretation is inherently ambiguous. We also show that cosmological observations already demonstrate some aspects of quantization that these proposals aim to test. Nevertheless, the proposed experiments would probe how gravity is sourced by spatial superpositions of matter, an untested new regime of quantum physics.

Keywords
Tabletop experiments, signatures of Quantum gravity
National Category
Other Physics Topics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-238908 (URN)10.1116/5.0101334 (DOI)001099661300001 ()2-s2.0-85144332552 (Scopus ID)
Available from: 2025-02-03 Created: 2025-02-03 Last updated: 2025-05-05Bibliographically approved
Eberhardt, A., Zamora, A., Kopp, M. & Abel, T. (2022). Single classical field description of interacting scalar fields. Physical Review D: covering particles, fields, gravitation, and cosmology, 105(3), Article ID 036012.
Open this publication in new window or tab >>Single classical field description of interacting scalar fields
2022 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 105, no 3, article id 036012Article in journal (Refereed) Published
Abstract [en]

We test the degree to which interacting Bosonic systems can be approximated by a classical field as total occupation number is increased. This is done with our publicly available code repository, QIBS, a new massively parallel solver for these systems. We use a number of toy models well studied in the literature and track when the classical field description admits quantum corrections, called the quantum breaktime. This allows us to test claims in the literature regarding the rate of convergence of these systems to the classical evolution. We test a number of initial conditions, including coherent states, number eigenstates, and field number states. We find that of these initial conditions, only number eigenstates do not converge to the classical evolution as occupation number is increased. We find that systems most similar to scalar field dark matter exhibit a logarithmic enhancement in the quantum breaktime with total occupation number. Systems with contact interactions or with field number state initial conditions, and linear dispersions, exhibit a power law enhancement. Finally, we find that the breaktime scaling depends on both model interactions and initial conditions.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:su:diva-203134 (URN)10.1103/PhysRevD.105.036012 (DOI)000761170800003 ()2-s2.0-85126015434 (Scopus ID)
Available from: 2022-03-23 Created: 2022-03-23 Last updated: 2022-03-23Bibliographically approved
Eberhardt, A., Kopp, M. & Abel, T. (2022). When quantum corrections alter the predictions of classical field theory for scalar field dark matter. Physical Review D: covering particles, fields, gravitation, and cosmology, 106(10), Article ID 103002.
Open this publication in new window or tab >>When quantum corrections alter the predictions of classical field theory for scalar field dark matter
2022 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 106, no 10, article id 103002Article in journal (Refereed) Published
Abstract [en]

We investigate the timescale on which quantum corrections alter the predictions of classical field theory for scalar field dark matter. This is accomplished by including second-order terms in the evolution proportional to the covariance of the field operators. When this covariance is no longer small compared to the mean field value, we say that the system has reached the “quantum breaktime,” and the predictions of classical field theory will begin to differ from those of the full quantum theory. While holding the classical field theory evolution fixed, we determine the change of the quantum breaktime as the total occupation number is increased. This provides a novel numerical estimation of the breaktime based at high occupations ntot and mode number N=256. We study the collapse of a sinusoidal overdensity in a single spatial dimension. We find that the breaktime scales as log(ntot) prior to shell crossing and then as a power law following the collapse. If we assume that the collapsing phase is representative of halos undergoing nonlinear growth, this implies that the quantum breaktime of typical systems may be as large as ∼30 of dynamical times even at occupations of ntot∼10100.

National Category
Other Physics Topics Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-212607 (URN)10.1103/PhysRevD.106.103002 (DOI)000886058300012 ()2-s2.0-85142174343 (Scopus ID)
Available from: 2022-12-09 Created: 2022-12-09 Last updated: 2022-12-09Bibliographically approved
Ilić, S., Kopp, M., Skordis, C. & Thomas, D. B. (2021). Dark matter properties through cosmic history. Physical Review D: covering particles, fields, gravitation, and cosmology, 104(4), Article ID 043520.
Open this publication in new window or tab >>Dark matter properties through cosmic history
2021 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 104, no 4, article id 043520Article in journal (Refereed) Published
Abstract [en]

We perform the first test of dark matter (DM) stress-energy evolution through cosmic history, using cosmic microwave background measurements supplemented with baryon acoustic oscillation data and the Hubble Space Telescope key project data. We constrain the DM equation of state (EoS) in 8 redshift bins, and its sound speed and (shear) viscosity in 9 redshift bins, finding no convincing evidence for non-ΛCDM values in any of the redshift bins. Despite this enlarged parameter space, the sound speed and viscosity are constrained relatively well at late times (due to the inclusion of CMB lensing), whereas the EoS is most strongly constrained around recombination. These results constrain for the first time the level of “coldness” required of DM across various cosmological epochs at both the background and perturbative levels. We show that simultaneously allowing time dependence for both the EoS and sound speed parameters shifts the posterior of the DM abundance before recombination to a higher value, while keeping the present day DM abundance similar to the ΛCDM value. This shifts the posterior for the present day Hubble constant compared to ΛCDM, suggesting that DM with time-dependent parameters is well-suited to explore possible solutions to persistent tensions within the ΛCDM model. We perform a detailed comparison with our previous study involving a vanishing sound speed and viscosity using the same datasets in order to explain the physical mechanism behind these shifts.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-198457 (URN)10.1103/PhysRevD.104.043520 (DOI)000686912800003 ()
Available from: 2021-11-08 Created: 2021-11-08 Last updated: 2022-02-25Bibliographically approved
Eberhardt, A., Kopp, M., Zamora, A. & Abel, T. (2021). Field moment expansion method for interacting bosonic systems. Physical Review D: covering particles, fields, gravitation, and cosmology, 104(8), Article ID 083007.
Open this publication in new window or tab >>Field moment expansion method for interacting bosonic systems
2021 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 104, no 8, article id 083007Article in journal (Refereed) Published
Abstract [en]

We introduce a numerical method and PYTHON package, CHiMES, that simulates quantum systems initially well approximated by mean field theory using a second order extension of the classical field approach. We call this the field moment expansion method. In this way, we can accurately approximate the evolution of first and second field moments beyond where the mean field theory breaks down. This allows us to estimate the quantum break time of a classical approximation without any calculations external to the theory. We investigate the accuracy of the field moment expansion using a number of well studied quantum test problems. Interacting bosonic systems similar to scalar field dark matter are chosen as test problems. We find that successful application of this method depends on two conditions: the quantum system must initially be well described by the classical theory, and the growth of the higher order moments must be hierarchical.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-198829 (URN)10.1103/PhysRevD.104.083007 (DOI)000704656000002 ()
Available from: 2021-11-16 Created: 2021-11-16 Last updated: 2022-02-25Bibliographically approved
Eberhardt, A., Banerjee, A., Kopp, M. & Abel, T. (2020). Investigating the use of field solvers for simulating classical systems. Physical Review D: covering particles, fields, gravitation, and cosmology, 101(4), Article ID 043011.
Open this publication in new window or tab >>Investigating the use of field solvers for simulating classical systems
2020 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 101, no 4, article id 043011Article in journal (Refereed) Published
Abstract [en]

We explore the use of field solvers as approximations of classical Vlasov-Poisson systems. This correspondence is investigated in both electrostatic and gravitational contexts. We demonstrate the ability of field solvers to be excellent approximations of problems with cold initial condition into the nonlinear regime. We also investigate extensions of the Schrodinger-Poisson system that employ multiple stacked cold streams, and the von Neumann-Poisson equation as methods that can successfully reproduce the classical evolution of warm initial conditions. We then discuss how appropriate simulation parameters need to be chosen to avoid interference terms, aliasing, and wave behavior in the field solver solutions. We present a series of criteria clarifying how parameters need to be chosen in order to effectively approximate classical solutions.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-180420 (URN)10.1103/PhysRevD.101.043011 (DOI)000513575900004 ()
Available from: 2020-03-30 Created: 2020-03-30 Last updated: 2022-02-26Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3875-9712

Search in DiVA

Show all publications