# Dark matter proposed to search on the surface of the Earth

(ORDO NEWS) — Physicists have modeled the behavior of hypothetical dark matter particles as they are captured by the gravity of stars and planets.

It turned out that as a result of this, noticeable concentrations of these particles can accumulate near the surface of celestial bodies, the authors declare 10 trillion particles per cubic centimeter near the Earth’s surface with a cross section of interaction with nucleons of the order of 10-29-10-28 square centimeters.

Despite a lot of indirect evidence of the existence of dark matter, a hypothetical form of matter that does not participate in electromagnetic interaction, it has not yet been possible to detect particles of such matter on detectors.

In addition, there is no final understanding of how these particles are arranged: different models predict different masses, cross sections for interaction with ordinary matter, and concentration distributions in space (to register dark matter, it is important to know not only the parameters of a single particle, but also to understand where they accumulate in significant amount).

Rebecca Leane from Stanford University and Juri Smirnov from the University of Liverpool proposed their own model that predicts the distribution of dark matter concentration near the surface of stars and planets.

The authors analyzed the scattering and reflection of dark matter particles on particles of the Standard Model (that is, ordinary matter).

As a result of multiple scatterings, dark matter particles gradually lose speed, and if this happens near a celestial body – a star or a planet – it may happen that the speed eventually turns out to be less than the second cosmic one, and then the gravity of the celestial body captures the particle.

Considering that the loss and annihilation of captured particles can be neglected, physicists determined the total number of dark matter particles in the volume of a celestial body as the product of the average rate of their capture (total for any number of scatterings for each particle) by the lifetime of this celestial body.

Then, in order to calculate the concentration of dark matter near the surface, the authors analytically modeled the diffusion and thermal conductivity of trapped dark matter particles in the volume of a spherical celestial body filled with ordinary matter.

At the same time, scientists believed that the concentration of dark matter is much less than the concentration of ordinary matter, and ordinary matter itself is in hydrostatic equilibrium and can be approximately described by the ideal gas equation of state.

According to the researchers, the choice of the latter is due to the fact that more accurate equations of state would complicate the calculations, but would only increase the predicted concentration of dark matter particles near the surface, which means that a simpler equation of state is sufficient for a lower estimate.

Using analytical results, the authors calculated the concentration of dark matter particles near the surface for the Earth, Jupiter, the Sun, and a brown dwarf with a mass of 50 Jupiters and an age of 10 billion years.

For simplicity, all objects except the Earth were considered by physicists to be composed entirely of hydrogen.

Scientists considered the surface layer a layer one kilometer thick for our planet (corresponding to the typical depth of underground experiments) and an area at a distance between 99.9 and 100 percent of the radius from the center of a celestial body for other objects.

It turned out that with optimistic values of the cross section for the interaction of dark matter with nucleons (of the order of 10–29–10–28 square centimeters), noticeable concentrations of dark particles will form near the surface of all considered celestial bodies: in particular, for the Earth, the concentration is estimated at 1013 particles per cubic centimeter , for the Sun – an order of magnitude more.

According to the authors, this motivates new searches for such surface particles in future experiments.

In addition, the researchers note that in the future, the results of the model can help predict how the dark matter captured by a celestial body affects the content of elements of ordinary matter in it – this could solve the problem of the solar composition (the discrepancy in the theoretical forecast and observational data for this composition at the level significance in six standard deviations).

Earlier, we talked about how the parameters of dark matter were limited using observations of Jupiter and how the accelerated expansion of the Universe was explained by the self-interaction of dark matter.

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