Paper Explainer: Mapping Dark Matter Through the Dust of the Milky Way Part I

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Paper Explainer: Mapping Dark Matter Through the Dust of the Milky Way Part I

This is work that I did with my student, Eric Putney, then-Rutgers-postdoc Sung Hak Lim (now at the Institute for Basic Science in Daejeon), and my colleague David Shih. This is actually a continuation of work we’ve been doing for a while, starting with a paper that tested the idea on synthetic data, and then a later paper applying it to real data. I didn’t write blog posts on those because I fell behind on everything starting in 2020 and I’m only just now digging myself out. This new paper is one of a pair, Part II will be coming out in the new year.

So what’s the big idea, and what are we doing now?

In short, we have a new method that takes the motion of stars in the Milky Way and learns the gravitational potential of all the stars and gas and dark matter in the Galaxy. It does this even in the regions where we can’t see most of the stars, due to dust obscuring their light, which is the new development above and beyond the previous work. This paper is about the method, and the next paper will give the results for the gravitational potential and the dark matter density we can learn from it.

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Paper Explainer: Inferring the Morphology of the Galactic Center Excess with Gaussian Processes

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Paper Explainer: Inferring the Morphology of the Galactic Center Excess with Gaussian Processes

This is a paper I wrote with Tracy Slatyer at MIT, her student Yitian Sun (now a postdoc in McGill), Sidd Mishra-Sharma (previously a postdoc at IAIFI, newly hired as a professor at Boston University), and my student Ed Ramirez. I think it is fair to say Ed did the majority of the analysis and coding on this (quite extensive) project, and was instrumental to the project from beginning to end..

This paper is a contribution to a long-running debate within the fields of particle physics and astrophysics, so it is fairly technical in parts, but the debate itself is very interesting and — I think — very important for the field of dark matter.

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Paper Explainer: Force-feeding Supermassive Black Holes with Dissipative Dark Matter

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Paper Explainer: Force-feeding Supermassive Black Holes with Dissipative Dark Matter

There is a problem in the early Universe, one that demands an answer.

Or maybe there isn’t. But at least, there is something weird going on in the data, and as a theorist, that’s good enough for me.

JWST, our newest space telescope, is capable of peering back further into the history of the Universe than previously possible. Sensitive to the infrared (IR) wavelengths, it can see the earliest stars whose visible light has been redshifted into the IR by the expansion of the Universe. Among its many surprising discoveries, it has identified a population of “little red dots” — early galaxies with a perhaps surprising number of stars given how early they are forming and with evidence of supermassive black holes with high masses already formed in their galactic cores.

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Paper Explainer: Dark Radiation Isocurvature from Cosmological Phase Transitions

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Paper Explainer: Dark Radiation Isocurvature from Cosmological Phase Transitions

I want to tell you about my most recent paper “Dark Radiation Isocurvature from Cosmological Phase Transitions,” which I wrote with my coauthors Mitch Weikert, Peizhi Du, and Nicolas Fernandez. Peizhi and Nico are postdocs here at Rutgers, and Mitch is my grad student. All three are great and fun to work with, and you should hire them.

As the title of the paper suggests, this is a project with a bunch of moving parts, and it’s not easy (even by the standards of theoretical physics research) to explain to outsiders. Which is unfortunate, because it has to do with what we know about the very early Universe, and how we know it. It’s one of those things that is really beautiful and tremendously informative, but complicated enough that its hard to convey how and why we know the things we know.

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Simulating a galaxy without a computer

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Simulating a galaxy without a computer

For particle physicists like myself, understanding how a galaxy works is critical for understanding how dark matter works at the particle level. All our evidence for the properties of dark matter, starting with its very existence and going from there, comes from its gravitational imprint on the visible matter. The physics of the very small influences the structure of some the largest objects in the Universe, and so by studying the latter, we learn about the former.

Which is why I’m going to share the story of an incredibly cool story of the earliest simulation of galaxies. Way back in 1941.

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Paper Explainer: Applying Liouville's Theorem to Gaia Data

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Paper Explainer: Applying Liouville's Theorem to Gaia Data

This is an explainer for my recent paper with David Hogg and Adrian Price-Whelan. This is a very different kind of paper for me, as evidenced by the fact that it is coming out on arXiv’s astro-ph (astrophysics) list and not even cross-listed to hep-ph (high energy phenomenology). In the end, the goal of the research that produced this paper is to learn about dark matter, but this paper by itself barely mentions the subject. There is a connection though.

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Paper Explainer: Direct Detection Anomalies in light of Gaia Data

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Paper Explainer: Direct Detection Anomalies in light of Gaia Data

This is an explainer for my recent paper with Gopolang (Gopi) Mohlabeng and Chris Murphy on the implications of recent surveys of dark matter velocity distributions from the Gaia mission on dark matter direct detection. There are a bunch of moving parts in this paper, as we’re trying to tie together some new directions from astrophysics with a long-standing problem in particle dark matter, so let me go through them.

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Paper Explainer: Gravitational probes of dark matter physics

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Paper Explainer: Gravitational probes of dark matter physics

The central thesis of the paper is that there is a huge potential to learn about the properties of dark matter: things like mass, interactions, production, etc using measurements from astronomy. This is not a completely novel idea: we know a great deal about dark matter from astronomy and cosmology (for example: dark matter is "cold" and not "hot"). However, there is an immense opportunity in the near future to do far more, thanks to improvements in simulation and some powerful new astronomical surveys which will be occurring. 

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Workshop talk: Mining LHC Data

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Workshop talk: Mining LHC Data

I'm at Fermilab for an LPC (LHC Physics Center) workshop on new ideas for LHC dark matter searches. I have been working with my fellow professor David Shih, postdocs Anthony DiFranzo and Angelo Monteux, and grad student Pouya Asadi at Rutgers on new ways to look for interesting anomalies in LHC data (see our paper and my blog post about it). Though not specifically about dark matter, it is a new idea, and so I have a talk about it. Here are the slides.

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TRISEP Summer School Lectures

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TRISEP Summer School Lectures

I'm up in Laurentian University in Sudbury, Ontario, giving three hours of lectures on "Beyond the Standard Model physics and the LHC" for the TRISEP Summer School.

TRISEP this year is mostly experimental grad students, and mostly experimental grad students working on experiments in the underground labs (such as SNOLAB in Sudbury). I'm the only lecturer who's talking about Beyond the Standard Model physics in general (though specific topics like dark matter and neutrino physics are being covered in more detail by other lecturers), and the only one talking about the LHC. Given that, and the audience, I ended up giving a broad overview: first on the sort of things we theorists have reason to think must exist beyond the Standard Model, then how the LHC works (always entertaining to have a theorist speak on how experiments work), and then lastly on how we look for new physics at the LHC. The slides are below.

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Paper Explainer: Collapsed Dark Matter Structures

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Paper Explainer: Collapsed Dark Matter Structures

This is a description of a paper I’ve written with my postdoc, Anthony DiFranzo. In our paper, we consider the possibility that dark matter could form gravitationally collapsed objects, evolving from an initial state of nearly uniform distribution across the Universe into one where it forms compact objects, analogous to have the regular matter that you and I are made of eventually formed stars and galaxies. Usually, we think this is not possible for dark matter, due to evidence that, on the largest scales, dark matter forms gravitationally bound structures that are much "fluffier" than the collapsed stars and galaxies. 

However, as we show in the paper, there is a way for dark matter to evolve into compact objects on small scales (say, a thousandth the size of the Milky Way), while still satisfying the constraints we've observed at larger scales. In demonstrating that it is possible for dark matter to do this, I think our paper makes an important point about some open questions in the field of dark matter research.

To explain why I started thinking about this particular project, I want to motivate it with a somewhat whimsical question.

Can there be planets and stars made of dark matter?

 

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Paper Explainer: Hiding Thermal Dark Matter with Leptons

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Paper Explainer: Hiding Thermal Dark Matter with Leptons

This is a description of my recent paper with my student David Feld. 

Dark matter is a problem. We know that there is a gravitational anomaly in galaxies: the stuff we can see is moving far too fast to be held together by its own gravity. Add to this the precision measurements of the echoes of the Big Bang (the Cosmic Microwave Background), which tells us that the way the Universe was expanding and matter was clumping cannot be explained without some new stuff that didn’t interact with light, and you have very solid evidence for the existence of dark matter. Then of course, there is the Bullet Cluster, where we can see the gravitational imprint of dark matter directly.

So we know it exists. We just don’t know what it is.

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Paper Explainer: Two is not always better than one: Single Top Quarks and Dark Matter

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Paper Explainer: Two is not always better than one: Single Top Quarks and Dark Matter

A few months ago, I was lucky enough to be contacted by an experimental student in the CMS collaboration, Deborah Pinna. Deborah had a question for me: in a certain set of dark matter models that I had written one of the early papers on, we only considered one particular class of final states, namely production of dark matter at the LHC along with a pair of top quarks. Why, she asked, did we not also consider the production of a single top quark, along with dark matter?

The answer was that everyone, including myself, just assumed that this channel didn’t matter. I’ll explain why in a bit, but I had just assumed that the rate at which this sort of event could occur would be so low that I never actually bothered to check. It turned out that my intuition was wrong. Deborah did check, and upon finding out that this single-top channel mattered, contacted me, assuming perhaps there was a good reason for ignoring it. There wasn’t.

I was really happy to contribute to Deborah’s project, and I want to emphasize that she and a postdoc, Alberto Zucchetta, did all of the heavy lifting on this paper.

So what was the idea? What is single versus pair production of tops, and why does it matter?

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Paper Explainer: Vector Boson Fusion Searches for Dark Matter at the LHC

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Paper Explainer: Vector Boson Fusion Searches for Dark Matter at the LHC

Here, I describe a recent paper I wrote with a group of experimentalists (Jim Brooke, Patrick Dunne, Bjoern Penning, and Miha Zgubic) and a Rutgers undergrad, John Tamanas. We investigated the ability of the Large Hadron Collider (LHC) to find dark matter using a particular type of event, one called “vector boson fusion,” or VBF.

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