11:15 〜 11:30
[PPS03-08] Searching for Primordial Dirac Magnetic Monopoles in a sample from Asteroid Ryugu returned by the Hayabusa2 mission
キーワード：Asteroids, Primitive Solar System Materials, Grand Unified Field Theories, Natural Remanent Magnetism
Dirac [1] demonstrated that the presence of even a single elementary particle with magnetic charge, a magnetic monopole, would force all electric charge in the universe to be quantized. This provided an elegant explanation for the observed quantization of electric charge and makes Maxwell's equations fully symmetric. Virtually every high-energy particle physics experiment includes a monopole search because their possible existence is so important to the foundations of Science.
Interest in monopoles intensified further after the mid 1970s when the work of Polyakov and ‘t Hooft [2, 3] led others to show that Grand Unified Field Theories predicted copious production of super-heavy magnetic monopoles during the high temperatures of the Big Bang. The mass of these monopoles is related to the unification scale on the order of 1016 GeV, which translates to about 10 nanograms located in a region of about 10-28 cm in size. The actual discovery and recovery of any magnetic monopoles that could be manipulated and studied in a laboratory would fundamentally transform Physics.
Primordial monopoles might still be trapped in primitive asteroids and comets [4]. Cosmic monopoles traveling through ionized giant molecular gas clouds should eventually lose their kinetic energy and come to rest with respect to dust particles, allowing them to stick to Ni-Fe flakes or other ferromagnetic particles. It is thought that these materials were gently accreted into the building materials of all asteroids and comets. Only the intense acceleration and heating during accretion to planets like Earth would dislodge them. Samples that were returned gently by JAXA from Itokawa and Ryugu might now be the only materials present on the surface of the Earth that could still retain trapped GUT Dirac Magnetic Monopoles and be accessible to Human study.
A simple and definitive test for the presence of Dirac magnetic monopoles is to pass them completely through a superconducting ring and monitor the change in magnetic flux with SQUIDs. A Dirac magnetic monopole should have quantized flux in multiples of 2Φo (= 2πℏ/e), where Φo is the flux quantum of superconductivity. Standard SQUID rock magnetometers that are in use in dozens of paleomagnetic laboratories can detect these particles in room-temperature samples with S/N ratios > 100. Using this technique, we examined a 1.3 mg sample (#C0058) of Ryugu returned by Hayabusa2 in three separate 2G instruments at the University of Tokyo, the Kochi Marine Core Center, and at Caltech. Pass-through measurements in all laboratories constrain the magnetic charge to be < 1% of a 2Φo Dirac charge, consistent with the absence of Dirac monopoles. Scanning SQUID imaging at Kochi and Caltech confirmed this result.
We also measured the Natural Remanent Magnetization (NRM) of the sample to be ~1.2 x 10-3 Am2/kg, in general agreement with recent work by Sato et al. [5]. However, the SQUID imaging in the Caltech and Kochi labs has revealed the presence multiple strong magnetic dipole sources with disperse orientations. The moments of these smaller dipoles are comparable to that of the main sample, arguing for mm-scale brecciation of the parent body consistent with the low external field of Ryugu. The observed magnetization distribution is consistent with observations that the Ryugu particles consist of brecciated fragments at the 100 – 1000 µm scale [6]. This would complicate paleointensity measurements.
We argue that all samples returned from space missions should be screened for the possible presence of Dirac Monopoles as part of the initial sample characterization protocols.
1. Dirac, P.A.M., Proc.R. Soc.London Series a, 1931. 133(821): p. 60-72.
2. Polyakov, A.M., Jetp Letters, 1974. 20(6): p. 194-195.
3. ’t Hooft, G., Nuclear Physics B, 1974. B 79(2): p. 276-284.
4. Kovalik, J.M. and J.L. Kirschvink, Phys. Rev. A, 1986. 33: p. 1183-1187.
5. Sato, M., et al.. JGR-Planets, 2022. 127(11).
6. Nakamura, T., et al.. Science, 2022. eabn8671.
Interest in monopoles intensified further after the mid 1970s when the work of Polyakov and ‘t Hooft [2, 3] led others to show that Grand Unified Field Theories predicted copious production of super-heavy magnetic monopoles during the high temperatures of the Big Bang. The mass of these monopoles is related to the unification scale on the order of 1016 GeV, which translates to about 10 nanograms located in a region of about 10-28 cm in size. The actual discovery and recovery of any magnetic monopoles that could be manipulated and studied in a laboratory would fundamentally transform Physics.
Primordial monopoles might still be trapped in primitive asteroids and comets [4]. Cosmic monopoles traveling through ionized giant molecular gas clouds should eventually lose their kinetic energy and come to rest with respect to dust particles, allowing them to stick to Ni-Fe flakes or other ferromagnetic particles. It is thought that these materials were gently accreted into the building materials of all asteroids and comets. Only the intense acceleration and heating during accretion to planets like Earth would dislodge them. Samples that were returned gently by JAXA from Itokawa and Ryugu might now be the only materials present on the surface of the Earth that could still retain trapped GUT Dirac Magnetic Monopoles and be accessible to Human study.
A simple and definitive test for the presence of Dirac magnetic monopoles is to pass them completely through a superconducting ring and monitor the change in magnetic flux with SQUIDs. A Dirac magnetic monopole should have quantized flux in multiples of 2Φo (= 2πℏ/e), where Φo is the flux quantum of superconductivity. Standard SQUID rock magnetometers that are in use in dozens of paleomagnetic laboratories can detect these particles in room-temperature samples with S/N ratios > 100. Using this technique, we examined a 1.3 mg sample (#C0058) of Ryugu returned by Hayabusa2 in three separate 2G instruments at the University of Tokyo, the Kochi Marine Core Center, and at Caltech. Pass-through measurements in all laboratories constrain the magnetic charge to be < 1% of a 2Φo Dirac charge, consistent with the absence of Dirac monopoles. Scanning SQUID imaging at Kochi and Caltech confirmed this result.
We also measured the Natural Remanent Magnetization (NRM) of the sample to be ~1.2 x 10-3 Am2/kg, in general agreement with recent work by Sato et al. [5]. However, the SQUID imaging in the Caltech and Kochi labs has revealed the presence multiple strong magnetic dipole sources with disperse orientations. The moments of these smaller dipoles are comparable to that of the main sample, arguing for mm-scale brecciation of the parent body consistent with the low external field of Ryugu. The observed magnetization distribution is consistent with observations that the Ryugu particles consist of brecciated fragments at the 100 – 1000 µm scale [6]. This would complicate paleointensity measurements.
We argue that all samples returned from space missions should be screened for the possible presence of Dirac Monopoles as part of the initial sample characterization protocols.
1. Dirac, P.A.M., Proc.R. Soc.London Series a, 1931. 133(821): p. 60-72.
2. Polyakov, A.M., Jetp Letters, 1974. 20(6): p. 194-195.
3. ’t Hooft, G., Nuclear Physics B, 1974. B 79(2): p. 276-284.
4. Kovalik, J.M. and J.L. Kirschvink, Phys. Rev. A, 1986. 33: p. 1183-1187.
5. Sato, M., et al.. JGR-Planets, 2022. 127(11).
6. Nakamura, T., et al.. Science, 2022. eabn8671.