Milena Crnogorčević

You are welcome to join the zoom event on high energy physics on October 30th at 13.00!
Speakers: Frank Wilczek, Sara Strandberg, Oksana Iarygina, and Oliver Schlotterer. The event will be moderated by Jonas Enander.
You'll find the zoom link here: indico.fysik.su.se/event/9415/ Welcome!

honored to summarize the work of so many brilliant colleagues pushing the boundaries of what we can (and can't yet) detect.

tl;dr: direct detection meets neutrino floor; indirect searches go truly multimessenger; non-WIMPs move to center; structural convergence of communities; where are we now & where are we headed---and more.

The Dark Matters at ICRC 2025 The dark matter track at ICRC~2025 showed a field in transition. Direct detection has entered the \emph{neutrino-floor era}, with XENONnT and PandaX-4T now limited by Solar neutrinos. Indirect searche...

At the International Cosmic Ray Conference (ICRC) 2025, while dark matter still refused to interact with our experiments, 1000+ of us joyfully interacted about the dark matter. ICRC 2025 dark matter rapporteur by yours truly available now for your perusing: arxiv.org/abs/2510.17473 🕵️‍♀️

Today's #PhotoOfTheWeek features AMS-02, a magnetic spectrometer for particle physics that has been operating on the International Space Station since 2011.

As someone who works on NASA missions, I can say this budget is cataclysmic—for science and for humanity. If passed, the consequences will be immediate and very hard—if not impossible—to reverse.
I beg and urge everyone who can to contact their Congress reps. Info: www.planetary.org/save-nasa-sc...

This photograph captures Sir David Attenborough seated outdoors on the rugged terrain of Skomer Island. Behind him, the ocean and coastal cliffs form a scenic backdrop under a clear sky. Sir David, dressed in a khaki jacket and light trousers, looks towards the camera with a gentle expression, exuding a sense of warmth, calm, and wisdom. Around him, puffins can be seen flying and perched on the rocky ground, illuminated in rays of golden sunlight as the sun sets behind the cliffs.

Happy 99th birthday to the man who gave voice to the wild. 🎉

Sir David Attenborough, thank you for a lifetime dedicated to the natural world, and for sharing its story with wisdom, wonder, and grace.

You've inspired generations to fall in love with nature.

In the centre is an elliptical galaxy, seen as an oval-shaped glow around a small bright core. Around this is wrapped a broad band of light, appearing like a spiral galaxy stretched and warped into a ring, with bright blue lines drawn through it where the spiral arms have been stretched into circles. A few distant objects are visible around the ring on a black background.

🆕 This new NASA/ESA/CSA James #Webb Space Telescope image shows a rare cosmic phenomenon called an 'Einstein ring' 🧪🔭

www.esa.int/ESA_Multimed... @science.esa.int @spacetelescope.bsky.social

Looking for the γ-Ray Cascades of the KM3-230213A Neutrino Source The extreme energy of the KM3-230213A event could transform our understanding of the most energetic sources in the Universe. However, it also reveals an inconsistency between the KM3NeT detection and ...

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that's where this story ends---for now. continued monitoring with Fermi and future gamma-ray missions (especially in the MeV band) could give us the full picture.

📖 In the meantime, take a look at this event with us:
arxiv.org/abs/2503.16606

🧪⚛️

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what are these two bright dots here, you ask?

we also checked two gamma ray sources nearby. one was too soft (wrong kind of spectrum), and the other (albeit harder spectrum) was the brightest 13 years *before* the neutrino showed up.

so neither is our likely culprit.

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here’s one takeaway: with no gamma rays, we can rule out a bunch of possible combinations of source distance (redshift z) and intergalactic magnetic field strength (B) that would produce a detectable cascade.

[Shaded regions = excluded by Fermi-LAT non-detection of gamma-ray cascade]

[11/]
maybe...

🤔 ...the source was far away---so far that the cascade light is too faint to detect, or
🤔 ...the space between was full of strong magnetic fields---which scattered the gamma rays, or
🤔 ...the source is "hidden"---buried in dust and matter that absorbed the light before it escaped.

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if there were gamma rays, and we didn’t see them, that tells us something about the universe between us and the source.

like...

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🚫 We find no cascade. No obvious counterpart in the gamma-ray sky.

But this is still interesting---I promise!

[here’s a sneak-peak into the year-by-year look at the gamma-ray sky around the neutrino.]

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Now is the time to welcome our favorite space-based gamma-ray observatory, Fermi! 🛰️

So, we dig into 17 years of Fermi-LAT data... searching really hard around the neutrino location in all kinds of time intervals, looking for steady signals or flares.
And…

[7/]

This just means we have to think a bit harder about the signal we are searching for, but fret not---Carlos' code to the rescue! We use a code called γ-Cascade to model how the gamma rays would travel, scatter, and arrive at Earth. 🧑‍💻

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If a neutrino this powerful was detected, where are the gamma rays that should follow it?

Well, we can look for them. But there is a catch: high-energy gamma rays can't travel very far through space---they crash into the cosmic background light and cascade down to lower energies (GeV--TeV).

[5/]

Charged pions decay into muons and -neutrinos-.
Neutral pions decay into -gamma rays-.

If neutrinos are being produced in these processes, gamma rays should be created right alongside them.

Also, lucky for us: gamma rays interact more readily with detectors!

[4/]

Let's put our physicist's hat on and ask: how was this high-energy neutrino produced?

We suspect it was produced in a hadronic interaction---where a high-energy cosmic ray---crashes into surrounding matter or light.

This kind of collision creates unstable particles: pions.

[3/]

Neutrinos barely interact with our usual surroundings. they zip through planets, stars... about 100 trillion neutrinos pass through our bodies every second.

Detecting a neutrino is hard. Detecting one with this energy?

Unprecedented.

[2/]

like...a lot.

30x more than the previous highest-energy neutrino.

or... think about the most powerful accelerator on Earth (Large Hadron Collider). LHC smashes particles at 13.6 TeV. This neutrino had ~220,000 TeV --- packed into *one tiny particle*.

[1/]
back in February 2023, the KM3NeT detector---sitting 3 km deep in the Mediterranean Sea---saw a neutrino so energetic, it shattered records.

Neutrino KM3-230213A carried ~220 PeV of energy.

that's a lot.

📜 HOT OFF THE PRESS: Carlos Blanco, @trlinden.bsky.social, and yours truly searched for gamma-ray counterpart to the *most* energetic neutrino ever seen! #KM3NeT

what we found (and didn't find) helps us understand the high-energy universe a bit better! let's dig in. 🧵

YouTube video by The Oskar Klein Centre Exploring the Universe from La Palma

🍿 Plan for the weekend! Our observers Cameron Lemon and Nikki Arendse from the Oskar Klein Centre in Sweden made a high quality documentary footage during their last visit to NOT.

🔭 Thank you for this great outreach action!

m.youtube.com/watch?v=TnPP...

@stockholmuni.bsky.social #telescope

Thanks for the comment and bringing the paper to my attention, Kev --- I remember discussing it in our group last year! Very interesting and relevant to our work as well.

8/ 🦁 Finally, a special shoutout to Nadia Kuritzén, a HIGH SCHOOL STUDENT who did a lion's share of the data analysis! Colleges, keep an eye out!

📄 Full Paper: arxiv.org/abs/2501.14865
#DarkMatter #GammaRays #Astrophysics #FermiLAT

7/ ...our work also motivates the importance of future gamma-ray instruments (like CTA, or prospective MeV missions) to push these bounds even further (or maybe detect some of DM particles)!

I, for one, can't wait to see what the future holds!

6/ ✨ Why is This Exciting?
1) it challenges DM explanation of the Galactic Center Excess, a long-standing mystery in gamma-ray astronomy
2) it reshapes where we look for DM and puts clusters as crucial testing grounds for future searches
3) but that's not all...

Upper limits on the dark matter annihilation cross-section to bb final state in the Virgo cluster. Our limits (magenta solid) rule out the thermal annihilation cross-section (black dashed) for dark matter masses below 200 GeV, exceeding constraints from the stacking of dwarf spheroidal galaxies (blue dashed) and from the IGRB (orange dashed). These results are in tension with dark matter explanations for the Galactic Center Excess (green region). The light-shaded region indicates the excluded parameter space.

5/ 🤯 The Results?
No big gamma-ray excess---but a null result can be incredibly powerful! We set some of the tightest constraints on DM annihilation below a few hundred GeV.