Ben Safdi
@bensafdi.bsky.social
Theoretical particle physicist at UC Berkeley looking for dark matter. Let me know if you find it! When not not-finding dark matter, I like to climb.
Pinned
Ben Safdi
@bensafdi.bsky.social
· Jul 23
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...
arxiv.org
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.
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.
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...
arxiv.org
July 23, 2025 at 8:19 AM
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.
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!
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...
arxiv.org
June 11, 2025 at 8:27 AM
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
May 29, 2025 at 7:26 AM
Fun times at PLANCK 2025 in Padua
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.
String Theory and Grand Unification Suggest a Sub-Microelectronvolt QCD Axion
YouTube video by Berkeley hepph video abstracts
youtu.be
May 23, 2025 at 7:08 PM
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.
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!
Search for Axions in Magnetic White Dwarf Polarization at Lick and Keck Observatories
YouTube video by Berkeley hepph video abstracts
youtu.be
April 18, 2025 at 3:45 PM
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!
😔
The decision came as the Trump administration has threatened to withhold funding from universities with DEI initiatives.
UC to no longer require diversity statements in faculty hiring
The decision came as the Trump administration has threatened to withhold funding from universities with DEI initiatives.
www.berkeleyside.org
March 20, 2025 at 4:23 PM
😔
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!
Probing the Axion-Electron Coupling with NuSTAR Observations of Galaxies
YouTube video by Berkeley hepph video abstracts
youtu.be
March 14, 2025 at 4:25 AM
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!
Reposted by Ben Safdi
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...
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.
www.berkeleyscanner.com
March 3, 2025 at 7:37 PM
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...
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 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...
indico.physics.lbl.gov
February 25, 2025 at 6:10 PM
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!
Reposted by Ben Safdi
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.
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.
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.
www.BerkeleyBikePlan.org
February 16, 2025 at 2:39 AM
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.
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.
Reposted by Ben Safdi
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
February 14, 2025 at 3:29 PM
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.
Nearly 200,000 Danes are supporting a comedic petition to buy California from the U.S., in what appeared to be a jab at President Donald Trump’s repeated threats to seize Greenland, an autonomous territory of Denmark.
‘We’ll never run out of avocado toast’: Danes launch petition to buy California
After President Donald Trump’s threats to purchase Greenland, Denmark's citizens launched a petition to purchase California from the U.S.
www.sfchronicle.com
February 13, 2025 at 2:53 AM
I’m down for that.
Reposted by Ben Safdi
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.
February 9, 2025 at 9:59 PM
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.
Reposted by Ben Safdi
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.
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.
Science funding agency threatened with mass layoffs
National Science Foundation staff heard the plans at a meeting Tuesday.
www.politico.com
February 5, 2025 at 12:08 PM
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.
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.
I think I'm going to have to log off of the internet for a bit before the news cycle breaks my brain entirely. Hundreds of millennia of human evolution have not provided us the cognitive tools required to process this level of administrative chaos.
January 29, 2025 at 8:00 PM
My thoughts today, precisely.
Reposted by Ben Safdi
Berkeley’s updating its bike plan! Learn more and weigh in at upcoming events.
www.berkeleyside.org/2025/01/21/b...
www.berkeleyside.org/2025/01/21/b...
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.
www.berkeleyside.org
January 24, 2025 at 12:12 AM
Berkeley’s updating its bike plan! Learn more and weigh in at upcoming events.
www.berkeleyside.org/2025/01/21/b...
www.berkeleyside.org/2025/01/21/b...
Reposted by Ben Safdi
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.
January 23, 2025 at 12:43 AM
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.
January 19, 2025 at 1:51 AM
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 🏄♂️
January 15, 2025 at 1:13 AM
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 🏄♂️
Reposted by Ben Safdi
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)
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)
January 12, 2025 at 5:25 PM
Josh Ruderman doing a heroic job on the “Joy of Dark Matter” at KITP
January 10, 2025 at 11:31 PM
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.
January 10, 2025 at 5:40 AM
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.
