Astronomy Colloquium for 2018-10-31

Series: Astronomy Colloquium
Date: Wednesday 31-Oct-2018
Time: 16:05-17:00 (4:05-5:00 pm)
Location: ATL 2400
Speaker: Dr. David Neufeld (JHU/UMD)
Title: Dark matter that interacts with baryons: density distribution within the Earth, new constraints on the interaction cross-section, and a dark matter search currently under way in my basement

For dark matter (DM) particles with masses in the 0.6 - 6 proton mass range, we may set stringent constraints on the interaction cross-sections for scattering with ordinary baryonic matter. These constraints follow from the recognition that such particles can be captured by - and thermalized within - the Earth, leading to a substantial accumulation and concentration of DM that interact with baryons. I will discuss the probability that DM intercepted by the Earth will be captured, the number of DM particles thereby accumulated over Earth's lifetime, the fraction of such particles retained in the face of evaporation, and the density distribution of such particles within the Earth. This analysis provides an estimate of the DM particle density at Earth's surface, which may exceed 1.E+14 cm-3, and leads to constraints on various scattering cross-sections, which are placed by: (1) the lifetime of the relativistic proton beam at the Large Hadron Collider; (2) the orbital decay of spacecraft in low Earth orbit; (3) the vaporization rate of cryogenic liquids in well-insulated storage dewars; and (4) the thermal conductivity of Earth's crust. For the scattering cross-sections that were invoked recently in Barkana's original explanation for the anomalously deep 21 cm absorption reported by EDGES, DM particle masses in the 0.6 - 4 GeV/c^2 range are excluded. Finally, I will discuss a tabletop experiment (that we are currently conducting in my basement) to further constrain the interaction cross-sections for a variety of atomic nuclei.

Colloquia are usually preceded by espresso and ice cream at 1:45 pm outside room PSC 1150 and are followed by an informal reception at 5:15 pm in that room. Anyone interested in talking with the speaker, or being added to the colloquium announcement email list, should contact the colloquium organizer. Lunch will normally be reserved for the speaker to talk to graduate students.

Colloquium Organizer: Prof. Richard Mushotzky


Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.


Directions and information about parking can be found here.

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