Ben Safdi

Wino and Real Minimal Dark Matter Excluded by Fermi Gamma-Ray Observations We show that minimal, fermionic dark matter (DM) models in the $n$-dimensional representation of the weak force with zero hypercharge that make up 100% of the DM under the standard cosmological histor...

Excited to put out arxiv.org/abs/2507.15934 with Linda Xu (SLAC) where we use Fermi data to conclusively rule out the thermal wino as DM, in addition to the quintuplet and 7-plet. The doublet (higgsino) is the remaining, untested minimal DM model and a strong motivation for future searches.

Discovering the Higgsino at CTAO-North within the Decade We demonstrate that higgsino dark matter (DM) could be discovered within the next few years using the Cherenkov Telescope Array Observatory's soon-to-be-operational northern site (CTAO-North). A 1.1 T...

Higgsinos are one of the best-motivated WIMP dark matter candidates, but mostly invisible to direct detection. We showed today arxiv.org/abs/2506.08084 that the soon-to-be operational CTAO-North detectors in the Canary Islands might be able to detect higgsino annihilation in gamma-rays before 2030!

Fun times at PLANCK 2025 in Padua

YouTube video by Berkeley hepph video abstracts String Theory and Grand Unification Suggest a Sub-Microelectronvolt QCD Axion

New paper youtu.be/nuWv7HtBsTA arxiv.org/abs/2505.15884 out today showing that axions from string theory need to have sub-microelectronvolt masses to be consistent with grand unification. This provides additional motivation to think about experiments such as ABRACADABRA/DMRadio and CASPEr.

YouTube video by Berkeley hepph video abstracts Search for Axions in Magnetic White Dwarf Polarization at Lick and Keck Observatories

Fun paper youtu.be/Ma0Pc0M6v8k arxiv.org/abs/2504.12377 led by my grad student Josh Benabou along with Chris Dessert and Alex Filippenko's group in Berkeley astronomy. We used Keck and Lick to look for axion-induced polarization from white dwarfs. No luck this time -- but we set strong limits!

😔

YouTube video by Berkeley hepph video abstracts Probing the Axion-Electron Coupling with NuSTAR Observations of Galaxies

New paper - youtu.be/ZyNDm764obQ arxiv.org/abs/2503.09682 - searching for axions produced through the axion-electron coupling in stars converting to X-rays in galactic B-fields. We looked with NuSTAR data towards M82/M87/M31 and didn't see a signal, setting upper limits. The search continues!

New survey supports a strong Berkeley Bike Plan: Op-ed The authors commissioned a professional poll from a nonpartisan research agency to learn more about what Berkeley wants in its bike infrastructure.

Hey, Berkeley, it turns out a huge majority of us want more bike infrastructure. Don’t listen to all the haters, all the anti-safety Save Hopkins people, they represent less than 20% of folks. www.berkeleyscanner.com/2025/03/03/t...

Berkeley Axion Workshop 2025 Axion dark matter has deep motivations from string theory to the strong CP problem. However, only recently has it been understood how to build instruments that can probe much of the most well motivate...

We are hosting a workshop on axion physics at UC Berkeley and LBNL from May 7 - 9, 2025: indico.physics.lbl.gov/event/3134/. Talks will range from experiments to string theory. Abstract submission closes March 14 -- junior researchers are especially encouraged. Spread the word!

Berkeley Bike Plan Focused Update - Public Input Map & Survey The City of Berkeley is updating its Bicycle Plan for everyone who wants to bike or roll in Berkeley – including skateboarding, scooting, or other personal wheeled mobility devices.

Hey Berkeleyans! Does your kid bike to school? Do you wish they could but don't feel it's safe enough?

There’s a BUSD-specific listening session on the Bike Plan update: Tue 2/25, 6:30-8:30pm at King! Would be great to get input from families on how Berkeley can make it safer to bike to school.

WIMP-nucleon, spin-independent cross section as a function of the WIMP mass. The new COSINE-100 exclusion limit is shown as a black curve, together with the green and yellow 1- and 2-sigma band, respectively.

The COSINE-100 experiment in South Korea achieved an improved energy threshold of 0.7 keV in their NaI(Tl) crystals and now fully excludes the DAMA/LIBRA signal as originating from dark matter interactions: arxiv.org/abs/2501.13665

I’m down for that.

Let’s make Telegraph car-free! Join TFP on Monday at 7pm to make the next big step towards pedestrianizing the 2nd busiest pedestrian street in the East Bay.

Trump says he will personally investigate California high-speed rail project President Donald Trump says he will personally investigate California's high-speed rail project, claiming it is billions of dollars over budget.

Can we have no nice things anymore?

www.sfchronicle.com/california/a...

Science funding agency threatened with mass layoffs National Science Foundation staff heard the plans at a meeting Tuesday.

I don't know how else to put this: This is fucking insane.

NSF, a $10 billion grantmaking agency, is planning to lay off between a quarter and a half of its staff in the next two months.

My thoughts today, precisely.

Have views about Berkeley's bike lanes? The city wants to hear from you Pop-up events and listening sessions in January and February will focus on residents' priorities for the city's bike lane network.

Berkeley’s updating its bike plan! Learn more and weigh in at upcoming events.
www.berkeleyside.org/2025/01/21/b...

Diversity, equity, and inclusion are all good things. They don’t happen automatically, we have to actively work to bring them about. Shout it from the rooftops.

Such a pleasure to have lunch with Georg Raffelt today in Berkeley after the “Baha Balantekin and George Fuller Fest.” He is an inspiration and has been doing axion physics since well before it was cool 😎. Also very neat to hear stories about his time in Berkeley in the 80’s.

I had lots of fun today giving a blackboard talk at #kitp on “What is axion theory?” Any talk followed by surfing in the sunshine is a success 🏄‍♂️

An artist's impression of the Gaia spacecraft.

The @esa.int Gaia satellite will take its final scientific measurements on Wednesday. 🔭

This will conclude a 12 year series of continuous observations.

Larger Gaia data releases are still in progress, but Gaia has already had a HUGE impact on our understanding of the #milkyway.

(Image: ESA)

He was asked to give an intro set of lectures on dark matter to postdocs and faculty in adjacent fields. I believe he agreed so long as he “didn’t have to do rotation curves” 😆. It was actually super informative. He described effectively every known DM production mechanism.

Josh Ruderman doing a heroic job on the “Joy of Dark Matter” at KITP

Less than 2 weeks ago we were hiking in Malibu and playing on the beach in Pacific Palisades and Santa Monica. Absolutely tragic to see what is happening down there and especially surreal being in Santa Barbara, which is so close but also feeling — for now — very normal.

California has its problems but is a pretty amazing place. Spent the past two weeks on a family road trip from skiing in Tahoe to surfing the coast to rock climbing in Joshua Tree. Upcoming: #KITP at #UCSB to discuss "What is Particle Theory?"

So cool! I hope this will come to SF next to help support public transit and safer streets for bikers and pedestrians.

We searched with Fermi data towards 4 "recent" SN, from the 1600's to a SN from this year. No evidence for axions :-( -- 2 sigma from SN1987A, but it is busy in the LMC. Still, we ruled out a lot of parameter space and maybe this method leads to a future discovery. It is motivated parameter space!

We consider ~MeV - GeV axions that couple to QCD and QED, as expected if there are e.g. GUTs. They don't solve strong CP but also could exist with a lighter QCD axion that does, as in axiverse constructions. They are produced in supernovae and decay to gamma rays with significant time delays.