British physicists have shown that the effects associated with quantum gravity lead to strong restrictions on the possible mass of dark matter particles.
The ranges of allowable masses obtained in this way for different types of dark particles turned out to be significantly narrower than the earlier theoretical limitations, and exclude the existence of very light and very heavy particles of dark matter. In the future, such a result may be useful in the course of experimental searches for dark matter.
Evidence for the existence of dark matter
Physicists have a lot of indirect evidence for the existence of dark matter – a hypothetical form of matter that does not participate in electromagnetic interaction. Without the assumption of the existence of such a dark analog of ordinary matter, it is very difficult to explain a number of phenomena that physicists call hidden mass effects.
Moreover, these effects are manifested on a variety of spatial and temporal scales of our Universe. For example, dark matter makes it possible to simultaneously explain both the abnormally high rotational speeds of the peripheral regions of galaxies and the features in the data on relic microwave radiation, although these effects are based on completely different physics, and they arose at different stages of the evolution of the Universe.
Therefore, physicists are confident in the existence of dark matter, despite the fact that so far they have not been able to directly register it.
Dark matter, however, has no place in the Standard Model – a well-established theoretical construction in particle physics that accurately describes the accumulated body of experimental data in this area. Therefore, to describe the nature of dark matter, scientists need new theories, and to test the proposed hypotheses – experimental data on the characteristics of dark particles, the most important of which is their mass.
Narrowing down the ranges of allowable masses of dark matter
Previously proposed theoretical constructs said that the mass of dark matter particles should lie in the range between about 10 -22 eV and 10 19 GeV. Based on these limitations, experiments on the direct registration of dark matter are also designed. New theoretical limits on the mass of dark particles would allow narrowing the scope of experimental searches.
Now, Xavier Calmet and Folkert Kuipers from the University of Sussex have significantly narrowed the range of possible masses of dark matter particles in their theoretical study. In it, scientists used the generally accepted assumption that the interaction of dark matter with itself and with ordinary matter not through gravity is negligible. But it was possible to obtain stronger restrictions on the mass of dark matter precisely by considering the action of gravity on it and in its quantum form.
The supposed quantum nature of gravity gave physicists a limit on the upper mass limit: particles that are too heavy over the past lifetime of the universe would undergo decay due to quantum effects. In the case of dark particles that are too light, the effects of quantum gravity would lead to the appearance of the so-called fifth force.
During the study, the scientists considered the case of scalar and pseudoscalar (axions) dark matter particles, as well as dark fermions (with spin 1/2) and particles with spin 2, all of which were singlet with respect to the gauge transformation.
As a result, dark fermions were most strongly limited, the mass of which physicists placed in the range from 10 2 to 10 10 electron volts. Slightly weaker restrictions were obtained for scalar particles and dark matter with spin 2: for them, the permissible mass turned out to be between 10 -3 and 10 7 electron-volts.
The same values were obtained for dark axions if the laws of quantum gravity violate parity, in the opposite case, the mass of dark pseudoscalar particles should be between 10 -21 and 10 7 electronvolts. In addition, physicists considered the case of a vector particle with spin 1: its mass was limited to 10 -22 and 10 7 electron-volts.
Scientists note that they received such restrictions by considering quantum gravity in the weakest of its possible variations, that is, acting on scales no more than the Planck mass. This is the worst option for the considered theory in terms of the strength of finite restrictions, and if quantum gravity is stronger, the resulting restrictions on the mass of dark matter will only increase.
On the other hand, it is also important that the results obtained are valid only for gauge-invariant fields: in the opposite case, the gauge invariance will “save” the particles from decay and the appearance of the fifth force, which means that the obtained restrictions will not apply.
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• Calmet, X., & Kuipers, F. (2021, January 13). Theoretical bounds on dark matter masses.
• Mann, A. (2020, September 22). What is dark matter?
• Metcalfe, T. (2021, February 05). Scientists narrow down the ‘weight’ of dark matter trillions of trillions of times.
• Sutter, P. (2021, February 06). Narrowing down the mass of dark matter.
• University of Sussex. (2021, January 27). How heavy is dark Matter? Scientists radically narrow the potential mass range for the first time.