Searching for Dark Matter: WIMPs, Axions and Others
Shengxuan Lin
San Gabriel Academy, San Gabriel, MyTown, U.S.A.
Keywords: Dark Matter, WIMPs, Axions, Sterile Neutrinos, Detection Methods.
Abstract: It’s widely accepted that dark matter makes up nearly 27% of the universe, yet its actual nature is still
unknown. Contemporarily, scholars have devised several ideas to explain this mysterious form of matter. Two
of the most talked-about candidates are WIMPs (Weakly Interacting Massive Particles) and axions, but others
like sterile neutrinos and even tiny black holes have also been suggested. This research will go through these
possibilities, focusing mainly on how researchers try to detect them. For WIMPs, one looks at direct detection
efforts deep underground, indirect searches using signals from space, and tests done in colliders such as the
LHC. For axions, one explains their theoretical background and how experiments like ADMX and CAST use
strong magnets and sensitive equipment to find them. This study also compares the latest results and points
out what areas scientists have already ruled out. While no confirmed signals have shown up so far, newer
tools and better methods are helping narrow things down. Understanding dark matter matters not just for
physics but also for figuring out how the universe came to be and how it behaves today.
1 INTRODUCTION
Even though one can see stars, galaxies, and gas
clouds in space, scientists say all of that only makes
up about 5% of the universe. A much larger part, i.e.,
roughly 27%, is something one can’t see at all: dark
matter. The idea of dark matter came up nearly a
hundred years ago when astronomers noticed that
galaxies were moving in ways that didn’t match what
one expected based on visible matter. In 1933, Fritz
Zwicky studied galaxy clusters and realized they
were moving too fast to be held together just by what
one could see (Zwicky, 1933). Later in the 1970s,
Vera Rubin found something similar while looking at
how stars move around in galaxies. Their speed didn’t
slow down at the edges like it should have, which
again hinted at some invisible mass (Rubin, et al., 1
980).
This mysterious substance, i.e., dark matte, isn’t
just interesting for astronomers. It’s super important
because it helps explain how galaxies formed in the
first place and how the universe looks today. The
most widely used model for understanding the
universe, called the ΛCDM model, actually depends
on dark matter to explain why galaxies and clusters
formed the way they did (Planck Collaboration,
2018). Scientists think if one figures out what dark
matter really is, it could help answer some of the
biggest questions in physics and even open the door
to new discoveries beyond what one knows now
(Bertone & Hooper, 2018).
While one knows dark matter is there because of
how it affects gravity, it is still unknown what it’s
made of. That’s why scientists have come up with
different ways to try to find it. Some are looking for
tiny particles called WIMPs (Weakly Interacting
Massive Particles), which are believed to rarely hit
normal atoms. There are giant underground
experiments like XENON1T and LUX-ZEPLIN that
are trying to catch these hits (Aprile et al., 2018; LZ
Collaboration, 2022). So far, they haven’t found
anything for sure, but they’ve managed to rule out
certain kinds of WIMPs, which helps focus the
search.
Others are studying axions, which are super light
particles that were originally suggested to fix a
problem in particle physics. Axions might be turning
into tiny bits of light (photons) when passing through
a magnetic field, and experiments like ADMX and
CAST are trying to catch that signal (Du, et al., 2018;
Anastassopoulos, et al., 2017).
Some scientists are also looking into other ideas,
like sterile neutrinos, particles that barely interact
with anything, or even mini black holes that might
have formed in the early universe (Carr, et al., 2020).
Tools like the Fermi Gamma-ray Telescope and the
Lin, S.
Searching for Dark Matter: WIMPs, Axions and Others.
DOI: 10.5220/0013821900004708
Paper published under CC license (CC BY-NC-ND 4.0)
In Proceedings of the 2nd International Conference on Innovations in Applied Mathematics, Physics, and Astronomy (IAMPA 2025), pages 193-198
ISBN: 978-989-758-774-0
Proceedings Copyright © 2025 by SCITEPRESS – Science and Technology Publications, Lda.
193

Large Hadron Collider (LHC) are also being used to
see if they can find any indirect signs of dark matter
(Aaboud, et al., 2017; Fermi-LAT Collaboration,
2015).
Even though no one has directly found dark
matter yet, the search has become more exciting
because one now has better technology and more
ideas. The goal of this paper is to take a closer look at
the three most talked-about types of dark matter
candidates: WIMPs, axions, and some of the more
unusual options like sterile neutrinos and tiny black
holes. Each type comes from different theories in
physics and requires different tools to detect.
The paper is organized into several parts. First,
this study will explain what dark matter is and the
main types that scientists think it might be. Then, this
study will go into more detail about WIMPs,
including what they are, how trying to detect them,
and what results gotten so far. After that, this study
will do the same for axions, talking about where they
come from and how scientists are searching for them.
The next section will focus on other possible dark
matter candidates that don’t get as much attention but
are still important. Finally, this study will compare all
of these options, what is still unknown, and what
future research might look like. By going over these
different ideas and experiments, this paper aims to
give a clear picture of where dark matter research
stands today and where it might go next.
2 DESCRIPTIONS
Most of what one sees in the universe, e.g., stars,
planets, and galaxies, only makes up a small part of
what’s out there. Scientists think that around 27% of
the universe is made of something called dark matter.
As shown in Fig. 1, the pie chart represents the
percentage of matter in the universe. Dark matter
cannot be observed for now, and it does not give off
light or energy, but one knows it is there because it
affects the things one sees. For example, galaxies spin
faster than they should base on the matter one can
detect. That tells scientists that something else must
be adding extra gravity (Bergström, 2012). Dark
matter can be split into two main groups: baryonic
and non-baryonic. Baryonic dark matter is made of
regular stuff like too-faint stars or black holes that
don’t shine. However, the problem is that there is just
not enough of this kind of matter to explain what one
sees in space. That is why scientists believe most dark
matter is non-baryonic, completely different from the
normal matter one knows (Feng, 2010).
Figure 1: Proportion of matter (Photo/Picture credit:
Original).
Non-baryonic dark matter is also sorted into types
based on how fast its particles were moving in the
early universe:
● Cold dark matter (CDM) is made of slow-
moving particles. They stick together and help form
galaxies. WIMPs, or Weakly Interacting Massive
Particles, are one of the top candidates for CDM
(Roszkowski et al., 2017).
● Warm dark matter (WDM) particles are a bit
faster and might explain some things that CDM can’t.
● Hot dark matter (HDM) moves really fast
(e.g., neutrinos), but this type doesn’t help form
structures very well.
So far, WIMPs are the most widely studied. These
particles would barely interact with normal matter,
which is why one hasn’t seen them directly. Scientists
use big labs like the Large Hadron Collider (LHC) to
try to create or spot them, but no proof has been found
yet (Roszkowski, et al., 2017). Another interesting
idea is the axion. This particle is super light and
comes from theories trying to fix problems in particle
physics. Axions might have been created early in the
universe, and scientists are now testing if they can
turn into light under certain conditions (Feng, 2010).
There’s also a theory about sterile neutrinos. They’d
be even harder to detect than regular neutrinos, but
some experiments are trying to find signs of them by
looking at how they might decay (Bergström, 2012).
In short, even though dark matter is still invisible to
us, one has good reasons to think it’s real. And with
better tools and ideas, scientists are slowly narrowing
down what it could be.
68%
27%
5%
Dark energy Dark matter Ordinary matter
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3 WIMPs
One of the most talked-about ideas for what dark
matter might be is something called WIMPs, or
Weakly Interacting Massive Particles. These are
particles that are thought to have mass and only
interact through gravity and the weak nuclear force,
which is why one can’t see or feel them. Even though
WIMPs haven’t been discovered yet, they’re still one
of the most popular dark matter candidates in modern
physics (Roszkowski, et al., 2018).
Because WIMPs don’t give off or reflect light,
scientists must look for them using indirect methods.
There are three main ways to do this: direct detection,
indirect detection, and particle collider experiments.
Direct detection is all about trying to “catch” a WIMP
as it passes through Earth. Scientists build
underground labs with detectors filled with liquid
xenon or argon. These detectors are placed deep
underground to block out background noise from
cosmic rays. One of the newest and most advanced
experiments is XENONnT, located in Italy. In 2023,
the team announced the results of their first run. They
didn’t find WIMPs yet, but they set some of the
strictest limits on what kind of WIMPs might still be
out there (Aprile, et al., 2023).
Another major direct detection experiment is
LUX-ZEPLIN (LZ), which is located in South
Dakota, USA. Like XENONnT, it uses liquid xenon
to detect tiny flashes of light caused by potential
WIMP collisions. The liquid xenon detector is filled
with very pure liquid xenon, and if a WIMPs hits a
xenon atom, it might cause a tiny flash of light or
release a small electric signals. And scientists use
these signals to figure out if a dark matter particle
might have passed through. Their first results,
published in 2022, didn’t detect any WIMPs either,
but just like XENONnT, the experiment helped rule
out many earlier models that are now considered
unlikely (LZ Collaboration, 2022).
The second method, indirect detection, doesn’t
look for WIMPs themselves but for the signals they
might leave behind. If two WIMPs smash into each
other, they could produce gamma rays or neutrinos.
Telescopes and detectors like Fermi or IceCube are
used to look for these kinds of signals. So far, none of
the signals have been strong or clear enough to
confirm the existence of WIMPs.
The third approach involves collider experiments,
especially at the Large Hadron Collider (LHC) in
Switzerland. This massive machine smashes particles
together at high speeds. If WIMPs are created in these
collisions, scientists might see signs like “missing
energy” in the data. But even though LHC results
from 2022 showed some unusual patterns, none of
them were strong enough to confirm a WIMP
discovery (ATLAS Collaboration, 2022).
Even though all three methods haven’t found
WIMPs yet, scientists aren’t giving up. In fact, each
experiment helps narrow down what WIMPs could
be, i.e., if they exist at all. These results help design
better detectors and improve future experiments.
Plus, the search for WIMPs is helping scientists better
understand the universe, even if the particles stay
hidden for now.
4 AXIONS
Axions are one of the lesser-known, but really
important, dark matter candidates. They weren’t
originally invented to explain dark matter. Instead,
they were proposed as a solution to a weird puzzle in
particle physics called the strong CP problem.
Basically, this is something that should make
particles behave in an unbalanced way—but in real
experiments, they don’t. So, scientists came up with
a new particle, the axion, to fix that. Later, they
realized axions also had the right properties to explain
dark matter. Because axions are tiny, stable, and don’t
interact much with regular matter, they could be
floating around in the universe without us noticing
them (Sikivie, 2021).
What makes axions different from other dark
matter particles like WIMPs is that they’re very light.
But even if they’re tiny, they could exist in huge
numbers; enough to make up a large part of the
universe. The problem is that they’re so weakly
interacting that one needs special tools to have a
chance of detecting them.
There are two main ways scientists are trying to
detect axions: haloscope and helioscope experiments.
Haloscope experiments look for axions in the galaxy
that might be passing through the Earth all the time.
These experiments rely on the fact that axions are
predicted to sometimes turn into photons (particles of
light) when they pass through a strong magnetic field.
That’s where detectors like ADMX come in. ADMX
stands for Axion Dark Matter eXperiment. It uses a
strong magnet and a special chamber called a
microwave cavity to look for tiny signals—like an
axion changing into a photon that gives off a bit of
energy (Bartram, et al., 2021).
Axion detectors are built around the idea that
these particles might very rarely turn into light when
they pass through strong magnetic fields. That’s why
many experiments use powerful magnets as their
main component. In halo scope setups like ADMX, a
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very strong magnet is placed around a microwave
cavity—a specially designed metal chamber that
resonates at certain frequencies. If an axion turns into
a photon inside the cavity, it will create a tiny amount
of energy that the system can pick up. The trick is that
the signal is extremely small, so the whole setup must
be kept super cold and shielded from noise to catch
even the slightest effect. On the other hand,
helioscope experiments like CAST and the upcoming
IAXO aim their magnets toward the Sun, hoping to
catch axions that might be flying out from it. If one of
those axions turns into a photon in the magnet, a
sensor can detect the light. These tools need to be
extremely precise, since the expected signals are
weaker than anything dealing with in everyday life.
That’s why scientists keep building better magnets
and more sensitive detectors. Even though one hasn’t
seen axions yet, every test brings us closer to either
finding them or ruling out where they might be
hiding.
The ADMX team made a big leap in 2021 by
searching a new range of axion masses. This range is
one of the most likely regions where axions are
predicted to be. They didn’t detect anything yet, but
they showed that the detector is sensitive enough to
find axions if they’re out there.
The other approach is called a helioscope. Instead
of looking for axions coming from space in general,
these detectors look at the Sun. Some theories say that
axions could be created in the Sun’s core and fly out
into space. When they pass through a magnet here on
Earth, they could turn into photons. The CERN Axion
Solar Telescope (CAST) did this for years. Now, a
newer, more powerful version called IAXO (the
International Axion Observatory) is being built. It
will have stronger magnets and better detectors,
which should make it possible to search a wider range
of axion masses (Irastorza & Redondo, 2022).
Other experiments like HAYSTAC and QUAX
are also trying different ways to find axions. Some are
using quantum sensors to boost their sensitivity. Even
though no one has found axions yet, more and more
of the possible axion “mass space” is being tested. In
physics, ruling things out is just as important as
making discoveries. The fact that axions might solve
not just one, but two big mysteries—dark matter and
the strong CP problem—makes them worth all the
effort. Axion research might not be as famous as
WIMPs or black holes, but it’s one of the most
promising areas in the search for dark matter. With
better tools and more experiments on the way,
scientists hope that one might be getting closer to the
answer.
5 OTHER CANDIDATES
Even though WIMPs and axions usually get most of
the attention when people talk about dark matter, they
aren’t the only ideas out there. Some scientists are
also looking into different kinds of particles or
objects, like neutrinos and primordial black holes
(PBHs). These aren’t new theories, but they’re still
being taken seriously and are part of the bigger search
to figure out what dark matter really is.
Neutrinos are super tiny particles that hardly
interact with anything at all. They’re flying through
everything (Earth, the bodies, even solid rock)
basically all the time, and one barely notices them.
Since they have a little bit of mass, they were once
thought to be a good candidate for dark matter. But
the thing is, they move fast. That makes them bad at
“clumping together,” which is something dark matter
has to do to help galaxies form. Because of that, most
scientists think neutrinos can’t be the main part of
dark matter. Still, some newer ideas suggest that in
certain conditions, like if they form something called
condensates, neutrinos might act more like slower-
moving cold dark matter and maybe be part of the
bigger picture (Buettner & Morley, 2022).
Then there are primordial black holes, which are
way different from the black holes one hears about in
space documentaries. These didn’t come from
exploding stars. Instead, they might have been
created right after the Big Bang, when parts of the
universe were so dense that they could’ve collapsed
into black holes. They could come in all sorts of
sizes—from teeny ones to one’s way bigger than the
Sun. Since they only mess with things through
gravity, they could totally act like dark matter. Some
scientists, (e.g., Carr & Kühnel, 2020), think it’s still
possible that PBHs could make up dark matter,
especially in a few mass ranges that haven’t been
ruled out yet.
Neutrinos are usually studied using huge
underground labs. One example is IceCube in
Antarctica. It’s basically a giant sensor frozen into the
ice that looks for tiny light flashes when a neutrino
hits something. It’s a cool setup and has helped us
learn a lot, but it hasn’t proven that neutrinos are the
dark matter looking for. PBHs are trickier. The
smallest ones should’ve already disappeared through
a process called Hawking radiation. But the bigger
ones might still be around. Scientists try to find them
by looking at how their gravity bends light from
faraway stars. This is called microlensing. Another
way is by looking for gravitational waves—ripples in
space made when black holes crash into each other.
LIGO has found some of these collisions, and a few
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scientists wonder if the black holes involved could’ve
been primordial.
Thus, neutrinos and PBHs aren’t the most popular
theories right now, but they haven’t been ruled out
either. And looking into all these different ideas helps
scientists keep an open mind. In the end, even if
they’re not the final answer, they’re helping us get
closer to figuring out what’s really going on in the
universe.
6 COMPARISON, LIMITATIONS
AND PROSPECTS
After learning about all the different dark matter
candidates, it's clear that each one has its strengths
and weaknesses. WIMPs, axions, neutrinos, and
primordial black holes all try to explain the same
mystery, but they come from totally different ideas in
physics.
WIMPs are still one of the most popular
candidates because they fit nicely with theories like
supersymmetry. They’re also supposed to have the
right kind of mass and speed to match how dark
matter should behave. The problem is that after
decades of searching, one still hasn’t found one.
Experiments like LUX-ZEPLIN and XENONnT are
super sensitive now, but they keep coming up empty.
Thus, while WIMPs still make sense on paper, it’s
hard to stay confident without real evidence.
Axions are different. They were invented for
something else, solving the strong CP problem in
particle physics, but ended up being a possible dark
matter solution too. What makes them cool is that
they're super light and barely interact with anything.
Experiments like ADMX are finally reaching the
sensitivity needed to look for them, and there’s a lot
of excitement about what future detectors like IAXO
might find. However, again, no solid results yet.
Then, there are the "other" candidates. Neutrinos
are interesting because one knows they exist, and they
have mass. Nevertheless, they move too fast to
explain how galaxies formed the way they did. Still,
people are thinking of ways they might act differently
under certain conditions. Primordial black holes are
probably the weirdest idea, they come from the early
universe and wouldn’t interact with anything except
gravity. There’s no need to invent new particles, but
it’s also hard to prove they’re even there. The big
limitation in all of this is the fact that scholars haven’t
found anything directly. Most of the work so far is
based on ruling things out rather than finding what
works. That’s frustrating, but it’s also part of science.
Human beings are asking questions no one has ever
answered before, and the tools one needs are just now
becoming good enough.
One big reason to be optimistic is that detection
technology is improving fast. Scientists are finding
ways to reduce background noise, cool detectors to
even lower temperatures, and use more stable
magnets. At the same time, new methods like
quantum sensing are helping increase sensitivity to
the tiniest signals. Another key improvement is in
energy resolution, the ability to tell apart very small
differences in energy. By designing better microwave
cavities and using more precise amplifiers,
experiments can now scan a narrower range of
frequencies more carefully. That means they’re less
likely to miss something just because it was slightly
outside the expected range. Bit by bit, these upgrades
make it more likely that one will finally catch a signal
that’s been hiding in the noise all along.
7 CONCLUSIONS
To sum up, the search for dark matter remains one of
the most important questions in modern physics. This
study examined several leading candidates: WIMPs,
axions, neutrinos, and primordial black holes. Each of
them offers a possible explanation, but none have
been confirmed. WIMPs were long considered the
most likely, but no direct evidence has been found.
Axion experiments are becoming more sensitive and
show promise. Neutrinos are well understood but
likely too light and fast. Primordial black holes
present an alternative approach but are difficult to
detect. Although no candidate has been verified,
ongoing experiments continue to narrow the
possibilities and improve the understanding. Every
test, even those that rule something out, brings us
closer to the truth.
REFERENCES
Aaboud, M., Aad, G., Abbott, B., et al., 2017. Search for
dark matter at √s = 13 TeV in final states containing an
energetic photon and large missing transverse
momentum with the ATLAS detector. European
Physical Journal C, 77, 393.
Anastassopoulos, V., Aune, S., Barth, K., et al., 2017. New
CAST limit on the axion–photon interaction. Nature
Physics, 13, 584–590.
Aprile, E., Aalbers, J., Agostini, F., et al., 2018. Dark matter
search results from a one ton-year exposure of
XENON1T. Physical Review Letters, 121(11), 111302.
Searching for Dark Matter: WIMPs, Axions and Others
197

Aprile, E., Aalbers, J., Agostini, F., et al., 2023. First Dark
Matter Search Results from the XENONnT
Experiment. Physical Review Letters, 131(3), 031001.
ATLAS Collaboration. 2022. Search for new phenomena in
events with an energetic jet and missing transverse
momentum in pp collisions at √s = 13 TeV with the
ATLAS detector. Journal of High Energy Physics,
2022(10), 61-91.
Bartram, C., Bowring, D., Carosi, G., et al., 2021. Search
for invisible axion dark matter in the 3.3–4.2 μeV mass
range. Physical Review Letters, 127(26), 261803.
Bergström, L., 2012. Dark matter evidence, particle physics
candidates and detection methods. Annalen der Physik,
524(9–10), 479–496.
Bertone, G., Hooper, D., 2018. A history of dark matter.
Reviews of Modern Physics, 90(4), 045002.
Buettner, D. J., Morley, P. D., 2022. Why not Neutrinos as
the Dark Matter? A Critical Review, KATRIN and New
Research Directions. arXiv preprint arXiv:2208.06460.
Carr, B., Kühnel, F., Sandstad, M., 2020. Primordial black
holes as dark matter. Annual Review of Nuclear and
Particle Science, 70, 355–394.
Du, N., Force, N., Khatiwada, R., et al., 2018. Search for
invisible axion dark matter with the Axion Dark Matter
Experiment. Physical Review Letters, 120(15), 151301.
Feng, J. L., 2010. Dark matter candidates from particle
physics and methods of detection. Annual Review of
Astronomy and Astrophysics, 48, 495–545.
Fermi-LAT Collaboration, 2015. Searching for dark matter
annihilation from Milky Way dwarf spheroidal galaxies
with six years of Fermi-LAT data. Physical Review
Letters, 115(23), 231301.
Irastorza, I. G., Redondo, J., 2022. The International Axion
Observatory: Status and prospects. Progress in Particle
and Nuclear Physics, 126, 103966.
LZ Collaboration., 2022. Results from the First Science
Run of the LUX-ZEPLIN Dark Matter Experiment.
Physical Review Letters, 129(6), 061101.
Planck Collaboration, 2018. Planck 2018 results. VI.
Cosmological parameters. Astronomy & Astrophysics,
641, A6.
Roszkowski, L., Sessolo, E. M., Trojanowski, S., 2018.
WIMP dark matter candidates and searches: Current
status and future prospects. Reports on Progress in
Physics, 81(6), 066201.
Rubin, V. C., Ford, W. K., Thonnard, N., 1980. Rotational
properties of 21 SC galaxies with a large range of
luminosities and radii. Astrophysical Journal, 238,
471–487.
Sikivie, P., 2021. Invisible axion search methods. Reviews
of Modern Physics, 93(1), 015004.
Smyth, N., Profumo, S., & English, S., 2020. Astrophysical
constraints on subsolar mass primordial black holes.
Physical Review D, 101(6), 063005.
Zwicky, F., 1933. Die Rotverschiebung von
extragalaktischen Nebeln. Helvetica Physica Acta, 6,
110–127.
IAMPA 2025 - The International Conference on Innovations in Applied Mathematics, Physics, and Astronomy
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