Dark matter day and the first GPS.DM results

Well, apparently dark matter day is a thing! And perfectly timed to this inaugural event is the publication of our first GPS.DM observatory results. Happy dark matter day!

Search for domain wall dark matter with atomic clocks on board global positioning system satellites

Benjamin M. Roberts,Geoffrey Blewitt, Conner Dailey, Mac Murphy, Maxim Pospelov, Alex Rollings, Jeff Sherman, Wyatt Williams & Andrei Derevianko

Nature Communications 8, Article number: 1195 (2017)


Cosmological observations indicate that dark matter makes up 85% of all matter in the universe yet its microscopic composition remains a mystery. Dark matter could arise from ultralight quantum fields that form macroscopic objects. Here we use the global positioning system as a ~ 50,000 km aperture dark matter detector to search for such objects in the form of domain walls. Global positioning system navigation relies on precision timing signals furnished by atomic clocks. As the Earth moves through the galactic dark matter halo, interactions with domain walls could cause a sequence of atomic clock perturbations that propagate through the satellite constellation at galactic velocities ~ 300 km s−1. Mining 16 years of archival data, we find no evidence for domain walls at our current sensitivity level. This improves the limits on certain quadratic scalar couplings of domain wall dark matter to standard model particles by several orders of magnitude.

Comprehensive review on precision measurements with atoms and molecules

Search for New Physics with Atoms and Molecules

M.S. Safronova, D. Budker, D. DeMille, D. F. Jackson Kimball, A. Derevianko, C. W. Clark

This article reviews recent developments in tests of fundamental physics using atoms and molecules, including the subjects of parity violation, searches for permanent electric dipole moments, tests of the CPT theorem and Lorentz symmetry, searches for spatiotemporal variation of fundamental constants, tests of quantum electrodynamics, tests of general relativity and the equivalence principle, searches for dark matter, dark energy and extra forces, and tests of the spin-statistics theorem. Key results are presented in the context of potential new physics and in the broader context of similar investigations in other fields. Ongoing and future experiments of the next decade are discussed.

Full text for this 112 page/24 fig. review is available at arXiv (https://arxiv.org/abs/1710.01833). The paper is currently under review in Reviews of Modern Physics.  Comments/corrections are welcome.

A data archive for storing precision measurements [Physics Today]

D. Budker and A. Derevianko, Physics Today, September 2015, page 10.

Precision measurements are essential to our understanding of the fundamental laws and symmetries of nature.

Traditionally, fundamental symmetry tests focused on effects that are either time independent or subject to periodic modulation due to Earth’s rotation about its axis or its revolution around the Sun. In recent years, however, attention has been drawn to time-varying effects, starting with the searches for a possible temporal variation of fundamental “constants.” Even more recently, researchers are looking for transient effects1 and oscillating effects2 due to ultralight bosonic particles that could be components of dark matter or dark energy.

To search for nonuniform dark energy or dark matter, researchers have proposed networks of atomic magnetometers and clocks.1The readings of remotely located network sensors are synchronized—for example, using the timing provided by GPS—and analyzed for specific transient features. Also being discussed are hybrid networks consisting of different types of sensors that would be sensitive to different possible interactions with the dark sector (see http://www.nature.com/nphys/journal/v10/n12/extref/nphys3137-s1.pdf).

A compelling example of time-stamped and stored datasets is the orbit and clock estimates of the Global Navigation Satellite Systems (GNSS) available through the International GNSS Service (http://igscb.jpl.nasa.gov). This service is the backbone of modern precision geodesy. The available multiyear archival data can be used to search for transient variations of fundamental constants associated with the galactic motion through the dark-matter halo (see http://www.dereviankogroup.com/gps-dm/).

The field of precision measurement appears to be undergoing a paradigm shift, with new theoretical and experimental ideas sprouting almost daily. For instance, reanalysis of data from using atomic dysprosium to look for the variation of the fine-structure constant and to test Lorentz invariance has set new limits on the scalar dark matter.3,4 That has been made possible by the existence of well-documented, accessible data sets stored electronically.

An example of a new experimental idea is using precise beam-position monitors in particle accelerators to test for specific types of Lorentz-invariance violations.5

Inspired by all those exciting developments, we propose that data streams from any ongoing precision measurements be time-stamped and stored for possible future analysis. We are convinced that the cost of data storage and GPS timing is relatively small and that the data storage will be straightforward to implement technically, though, of course, the price and complexity crucially depend on the precision of the time stamp and the data rate. Conversely, failing to time-stamp and store the data is likely to be an enormous waste. The search for transient effects of the dark sector is already a good motivation to create a data archive, and additional ideas of how to use such data are likely to emerge in the future.

What information should be time-stamped and recorded as a raw data stream? Data from optical and matter interferometers, experiments measuring parity violation and looking for permanent electric dipole moments, precision-measurement ion traps, all precision experiments with antimatter, and, by default, anything measured precisely.

We live in the age of Google and GPS; our thinking about experimental data should be keeping up with the times!

  1. S. Pustelny   525, 659 (2013); http://dx.doi.org/10.1002/andp.201300061
    A. Derevianko, M. Pospelov,  10, 933 (2014). http://dx.doi.org/10.1038/nphys3137
  2. P. W. Graham, S. Rajendran,  88, 035023 (2013); http://dx.doi.org/10.1103/PhysRevD.88.035023
    B. M. Roberts   90, 096005 (2014). http://dx.doi.org/10.1103/PhysRevD.90.096005
  3. K. V. Tilburg   115, 011802 (2015). http://dx.doi.org/10.1103/PhysRevLett.115.011802
  4. Y. V. Stadnik, V. V. Flambaum, arXiv:1504.01798.
  5. B. Wojtsekhowski,  108, 31001 (2014). http://dx.doi.org/10.1209/0295-5075/108/31001



Postdoctoral position GPS.DM collaboration

GPS.DM collaboration analyzes navigational satellite and terrestrial atomic clock data for  exotic physics signatures. In particular, the collaboration searches for transient variations of fundamental constants correlated with the Earth’s galactic motion through the dark matter halo. A postdoctoral associate will be primarily responsible for  mining  massive amounts of historic GPS data and developing statistical analysis.

The postdoc will be located at the University of Nevada, Reno and will be directly collaborating with Dr. Andrei Derevianko (Physics) and Dr. Geoffrey Blewitt (Nevada Geodetic Laboratory). Strong computational skills and familiarity with statistical analysis are preferred.

To apply please contact A. Derevianko (andrei_AT_unr.edu) or G. Blewitt (gblewitt_AT_unr.edu).

Dark matter search with GPS: Q&A

In the aftermath of our paper (with Maxim Pospelov) "Hunting for topological dark matter with atomic clocks" having been published, there were quite a number of e-mails with questions about our proposal. There was even an offer for a free-of-charge use of a powerful computational cluster (thank you!). I apologize for not answering all e-mails individually - just not enough time.  One of my friends has also sent me a link to this reddit thread - there is a genuine interest to the details of the proposal. This post is intended to answer some of these questions.

First of all see the previous post that outlines the basic idea of the search.

Topological dark matter: 
There are two components that go into dark-matter model building: (i) what the dark matter objects are and (ii) how these objects interact non-gravitationally with us (baryonic or ordinary matter). I emphasize the word non-gravitationally, as the gravitational interaction is a must due to multiple observations of gravitational interactions between dark and ordinary matter (and consistency with general relativity).

Additional model constraints come from various observations and cosmological simulations. Still the allowed parameter space is enormous: even if one were to assume that the dark matter objects are made out of elementary particles, the allowed masses span 50 orders (!) of magnitude. This is just a testament to the current state of confusion in modern physics and cosmology.  The field is ripe for discoveries.

First of all I admit that our model (due to Maxim Pospelov) is speculative, but it is as good as any model out there. WIMPs and axions have additional attractive features as they also might solve other outstanding problems in physics (for example, strong-CP problem in physics can be solved with axions).

So what is the model? (here you might get lost, just read on). For experts, technical discussion can be found in the extensive supplementary material to our paper.

Well, you start with a quantum field and this field has some self-interaction built in. The interaction is such that it allows for several identical minima. For example, the same value of potential minima could be reached at two distinct values of the field +A and -A. Now when the Universe expands it cools down and the field has to settle at the minima of the potential. The field is torn apart by which value to chose - the choice of +A or -A are equivalent. So in some regions of space it picks +A and in the other regions it picks -A. This is called "spontaneous symmetry breaking".

Nature does not like discontinuities and you have to smoothly connect  +A and  -A domains. This transition region is the topological defect or cosmic wall. The thickness of the wall is given by the particle Compton wavelength = h/(m c), where m is the particle mass, is the Plank constant and c is the speed of light.

This example is overly-simplistic but it demonstrates the idea of how topological defects are formed as the Universe cools down: in fact, for a dark-matter model you would like to have the field to be zero everywhere except inside the defects (see the supplement). All the energy (or mass) is stored in topological defects.

Depending on the field's degrees of freedom (scalar vs vector fields) and the self-interaction potential  one may form defects of various geometry: monopoles, strings or domain walls. Especially interesting is the case of monopoles (spherically-symmetric objects) as the gravitationally-interacting gas of monopoles mimics dark matter. The size of the defect is a free parameter - we do not have constraints on how large it could be. GPS would be sensitive to Earth-sized monopoles (huge Compton wavelength translating into particle mass ~10^-14 eV).

Here is a real-life example of spontaneous symmetry breaking and topological defects (due to Rafael Lang, the interview to appear in Sensing Our Planet magazine)

“There’s a wedding and a hundred people are sitting at this big round table. Somebody starts eating the salad. They pick up the fork on their left, so the person next to them has to pick up the fork on the left. Now the bride also starts eating, picking up the fork on the right, so everybody around the bride picks up the right fork. At some point in between this poor guy will be sitting with no fork; on his other side will be someone with two forks. Those two guys are called a topological defect. There’s nothing special going on around the left, the right, but where those two guys are sitting, there’s a disruption of the forks.”

Ok so we are done with choosing dark-matter objects. Now the second ingredient is the non-gravitational interaction between dark matter objects and us. Here you do need to pick one that is "reasonable" (e.g., Lorentz-invariant)  and is sufficiently weak that it went unnoticeable in dedicated experiments and observations. The interaction that we picked is of this kind. Effectively when the defect overlaps with us, it pulls on the particle (electron, proton, neutron, etc) masses and forces acting between the particles. Mind you this pull is really weak, otherwise we would have noticed it. However, there are ultra-sensitive devices, like atomic clocks (see this post) that may be sensitive to such pulls. You might ask - why it might have gone unnoticed before in atomic clocks -  some of the reasons are purely psychological and are related to how an experimentalist discerns signal from noisy background (see this post.)


A common mistake of beginners is the desire to understand everything completely right away. In real life understanding comes gradually, as one becomes accustomed to the new ideas. One of the difficulties of scientific research is that it is impossible to make progress without clear understanding, yet this understanding can come only from the work itself; every completed piece of research represents a victory over this contradiction.

 This quote comes from the preface of one of my favorite books "Qualitative Methods in Quantum Theory"  by a great practitioner of theoretical physics Arkady Migdal.

Nature bibliography style bst-file with no URLs

If you ever went through the grueling process of re-formatting your LaTeX manuscript to match Nature style, you would appreciate this  little trick.

A typical LaTeX distro includes nature package with nature.bst file included. *.bst files govern how the BibTeX bibliographies are formatted. The nature.bst file does not handle URLs well and Peter Komar  has hacked the original nature.bst file to remove URLs from the bibliography.

Peter has generously agreed to share his hack with the community.  The file naturemag_noURL.bst can be downloaded here.

The easiest solution is to place this file into the directory with your manuscript files and  to add  \bibliographystyle{naturemag_noURL} to your tex document.

Happy TeX-ing!