Searching Dark Matter Candidate Based on the State-of-Art

Facilities: Evidence from WIMPs and ALPs

Yingxu Zhao

Department of Astrophysics, Mcmaster University, Hamilton, Canada

Keywords: Dark Matter Search, WIMPs, ALPs.

Abstract: In contemporary astrophysics and cosmology, dark matter (DM) remains one of the most fundamental

mysteries, derived from its gravitational pull-on radiation, observable matter, and the universe's large-scale

structure. This study explores recent advancements in detecting DM candidates, focusing on WIMPs and

ALPs. Significant progress in WIMP detection is highlighted by the TREX-DM detector achieving a low

energy threshold and background level, enabling the exploration of sub-GeV WIMPs. Similarly,

advancements in ALP detection have been marked by innovative experiments leveraging strong magnetic

fields and novel techniques like nuclear magnetic resonance. These methods have improved sensitivity limits

and explored previously uncharted mass ranges and coupling constants. The continual refinement in detection

technologies and methodologies drives deeper investigations into DM properties. These advancements not

only set stringent limits on DM interaction cross-sections but also open new avenues for exploration in the

search for elusive DM candidates. This research is important because it can unravel the characteristics of DM,

advancing a thorough knowledge of the genesis and development of the universe and directing upcoming

astrophysical and cosmological research projects.

1 INTRODUCTION

Dark matter (DM) is one of the most profound

mysteries in modern astrophysics and cosmology. Its

gravitational pull-on radiation, observable matter,

and the universe's large-scale structure suggests its

existence. The concept of DM was first proposed by

Fritz Zwicky in the 1930s, when he observed the

peculiar motion of galaxies within the Coma Cluster,

suggesting the presence of unseen mass to account for

the observed gravitational effects (Zwicky, 1937).

For decades, evidence for DM has cumulated through

various astro observations, such as cosmic microwave

background (CMB) radiation, gravitational lensing,

and galaxy rotational curves (Rubin, 1970).

The significance of DM research is very crucial.

It is estimated that DM makes up roughly 27% of the

universe's total mass-energy content, this is in stark

contrast to 5% baryons which is ordinary matter. For

a complete picture of the creation and evolution of the

universe, understanding DM is essential (Bertone,

2018). Its elusive nature challenges the current

https://orcid.org/0009-0007-4449-9121

understanding of physics, pointing to potential new

particles and interactions beyond the Standard Model.

Recent developments in WIMPs detection have

been marked by the deployment of highly sensitive

detectors designed to identify rare interactions

between WIMPs and ordinary matter. The TREX-

DM detector has shown promising results through

reaching a background level of 80 counts

𝑘𝑒𝑉



𝑘𝑔



𝑑𝑎𝑦



in the 1 to 7 keV range, and a low

energy threshold of 1 keV. This sensitivity makes it

possible to investigate WIMPs with masses smaller

than 1 𝐺𝑒𝑉/𝑐



, which is a breakthrough in the area

(Castel, 2024). Ongoing improvements in reducing

background noise and lowering energy thresholds are

expected to further enhance the sensitivity of WIMP

detection. Parallel to WIMP research, Considerable

advancements have been achieved in the hunt for

ALPs. Considerable advancements have been

achieved in the hunt for ALPs, which are considered

another well-motivated DM candidate (Castel, 2024).

Current experiments have leveraged strong magnetic

fields to detect the electromagnetic interactions of

ALPs. A study using ferromagnets and SQUIDs

276

Zhao, Y.

Searching Dark Matter Candidate Based on the State-of-Art Facilities: Evidence from WIMPs and ALPs.

DOI: 10.5220/0013074900004601

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 1st International Conference on Innovations in Applied Mathematics, Physics and Astronomy (IAMPA 2024), pages 276-281

ISBN: 978-989-758-722-1

(Superconducting Quantum Interference Devices)

has pushed the boundaries of detection sensitivity,

improving restrictions in specific mass ranges on the

ALP-photon coupling constant (Gramolin, 2020).

These experiments have begun to explore the mass

and coupling regions where ALPs might explain

anomalies in TeV gamma-ray transparency, thus

opening new avenues in DM research. Previous

studies have also employed novel techniques like

nuclear magnetic resonance and spin-based

amplifiers to detect ALPs, significantly improving the

constraints on ALP-photon coupling. The

NASDUCK collaboration has achieved

unprecedented sensitivity in detecting the interactions

of ALPs with nucleons, covering a previously

unexplored mass range (Bloch, 2023).

The motivation for this research stems from the

ongoing gaps in the knowledge of the composition

and characteristics of DM. Despite extensive efforts,

the identity of DM remains unknown. This research

aims to contribute to the ongoing quest by exploring

various detection methods and theoretical models. By

synthesizing recent experimental results and

theoretical developments, this study seeks to provide

a comprehensive overview and propose new avenues

for investigation. The rest part of the paper is

organized as follows. The Sec. 2 introduces the

definition and classification of DM, including

potential candidates like WIMPs and axions, and their

theoretical underpinnings. The Sec. 3 focuses on the

theoretical description of axions, including Feynman

diagrams and scattering cross-sections, detection

methods, and typical instruments. It will present

recent results and include figures from relevant

studies. The Sec. 4 covers WIMPs, detailing their

theoretical framework, detection principles, and key

experiments. Recent findings will be discussed, with

accompanying charts and graphs from recent

literature. The Sec. 5 explores other DM candidates,

their theoretical models, and detection techniques.

Recent results will be illustrated with figures from

studies conducted in the past few years. The Sec. 6

discusses the current limitations of DM research and

outline potential future directions for overcoming

these challenges. Eventually, a conclude remark is

given in Sec. 7.

2 DESCRIPTIONS OF DM

Since DM doesn't emit, absorb, or reflect light, it is

invisible to telescopic technology as they exist now.

Even though its invisible, the gravitational pull of DM

on observable matter, such galaxies and stars,

suggests that DM exists. Fritz Zwicky first put up the

concept of DM in the 1930s when he noticed that a

galaxy's motion within clusters indicated the presence

of unseen mass, significantly exceeding the mass of

observable objects (Zwicky, 1937).

DM is broadly categorized into two types: cold

DM (CDM) and hot DM (HDM). CDM consists of

relatively massive particles that move slowly, while

HDM includes lighter particles that travel at higher

velocities (Press, 1990). For Cold Dark Matter

(CDM):

 WIMPs. Among the most well-liked CDM

contenders, WIMPs are hypothesized to interact

only via gravity and the weak nuclear force.

Their masses range from a few 𝐺𝑒𝑉/𝑐



to a few

𝑇𝑒𝑉/𝑐



 Axions. Axions are hypothetical particles with

extremely low masses, suggested as a solution

to strong CP problem in QCD. If they exist,

axions could also form part of the CDM (Peccei,

1977).

For Hot Dark Matter (HDM), there are some Light

Neutrinos. Early cosmological models considered

light neutrinos as potential HDM candidates.

Neutrinos are very light, travel at relativistic speeds,

and contribute minimally to the overall DM density

(Press, 1990).

The most auspicious applicants for DM include

WIMPs and axions. WIMPs are one of the leading

contenders for DM. They exclusively interact through

gravity and the weak nuclear force; neither the strong

nuclear force nor the electromagnetic force is

involved. WIMPs are classified as CDM due to their

relatively large mass and slow movement compared

to the speed of light. The "freeze-out" mechanism

describes how WIMPs decoupled from the thermal

equilibrium of the early cosmos, leading to the DM

density observed today. The density parameter for

WIMPs can be expressed as:

𝛺



ℎ















~(3 ×













〈







〉

) (1)

Here, Ω

denotes the density parameter, h denotes the

Hubble constant, ⟨σ

v⟩ denotes the average

interaction cross-section multiplied by the velocity

(Press, 1990). Axions are lightweight hypothetical

particles initially proposed to address the strong CP

problem in QCD. It is anticipated that their masses

will vary between 10



eV and 10



eV. Axions

interact weakly with photons, which allows indirect

detection methods. The density parameter for axions

can be described by the equation:

𝛺











=10



(









)(







)(









)



ℎ



(2)

Where Ωa is the density parameter, fa is the Peccei-

Quinn symmetry-breaking scale (Peccei, 1977).

Searching Dark Matter Candidate Based on the State-of-Art Facilities: Evidence from WIMPs and ALPs

277

Despite the fact that DM cannot be seen directly, it is

supported substantiated by cosmological

observations and gravitational effects. Candidates

such as WIMPs and axions offer plausible

explanations for DM. Ongoing and future

experiments aim to reveal more about the

characteristics of DM, advancing the comprehension

of the universe's composition and evolution.

3 SEARCHING FOR AXION

ALPs are hypothesized to address the strong CP

problem in QCD. They are pseudoscalar bosons with

no intrinsic spin. The axion-photon exchange is

described by the Lagrangian:

ℒ⊃−





𝑔



𝑎𝐹



𝐹





(3)

where a denotes the axion field, gaγγ denotes the

axion-photon coupling constant, 𝐹



denotes the

electromagnetic field tensor, and 𝐹





is its dual.

Feynman diagrams depict axion interactions, like the

conversion of photons to axions in a magnetic field

(Preskill, 1983).

A number of experimental strategies designed in

order to identify ALPs and axions., mainly relying on

their weak coupling to photons. Common methods

include:

 Haloscope Searches. In these studies, axions are

converted into observable photons by use of

high-quality-factor microwave cavities

submerged in a strong magnetic field.

 Helioscope Searches. These involve telescopes

intended to use a high magnetic field to

transform axions created in the Sun into X-rays,

which would then be detected.

 LSW Experiments. These experiments involve

shining a laser beam at a wall where axions are

expected to convert to photons, which can then

be detected on the other side of the wall.

 Axion Interferometry. This method exploits the

interference patterns produced by axion-

modulated laser beams in optical cavities

(Gramolin, 2020).

For typical detectors, there are several follows:

 ADMX. This haloscope experiment makes

advantage of a microwave cavity inside a strong

magnetic field to find axion-photon conversion

at specific resonance frequencies corresponding

to the axion mass range of interest.

 CAST. A helioscope that aims to find axions

created in the Sun by their conversion to X-rays

using a powerful magnet (Gramolin, 2020).

 ABRACADABRA. This experiment looks for

axion DM by detecting the magnetic fields

induced by axions in a toroidal magnet

configuration.

The SHAFT experiment demonstrated significant

improvements in response to DM that is axion-like.

The experiment enhanced the static magnetic field by

using toroidal magnets with ferromagnetic powder

cores made of iron-nickel alloy. The setup involved

two independent detection channels with stacked

toroids, each magnetized to create an oscillating

magnetic field detectable by SQUID magnetometers.

Results showed improved limits on a wide mass range

of the axion-photon coupling constant (Gramolin,

2020). The ADBC experiment proposed a novel

approach to interferometry employing a birefringent

cavity to detect axion-modulated laser light. Over a

broad range of axion masses, this architecture

improves sensitivity to the axion-photon coupling,

Using a realistic bowtie cavity design with adjustable

mirror angles. The expected limits on the axion

coupling from this experiment indicate significant

improvements over previous methods (Gramolin,

2020).

The results from these experiments typically

include exclusion plots showing the limitations of the

axion-photon coupling constant gaγγ in relation to the

mass of the axion ma. These plots help illustrate the

sensitivity improvements and the parameter space

explored by each experiment. Fig. 1 is an example of

a graphical representation from the SHAFT

experiment. It shows the axion-photon coupling

strength exclusion limits for various axion masses,

demonstrating the enhanced sensitivity of the SHAFT

experiment compared to previous limits set by the

CAST helioscope and other experiments (Gramolin,

2020).

Figure 1: Graphical representation from the SHAFT

experiment for searching cross sections (Gramolin, 2020).

IAMPA 2024 - International Conference on Innovations in Applied Mathematics, Physics and Astronomy

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4 SEARCHING FOR WIMPS

WIMPs are an ideal candidate for DM, arising

naturally in supersymmetric models as the lightest

supersymmetric particle. They communicate using

gravity and the weak nuclear force, and their

theoretical framework can be illustrated using

Feynman diagrams. A common interaction is the

destruction of WIMPs into particles in the Standard

Model through intermediate states like the Z boson or

the Higgs boson. The effective Lagrangian describing

WIMP interactions includes terms such as:

ℒ = ℒ

𝒮ℳ







𝑊







−











𝑊









𝐵





−











𝐵



+ . .. (4)

where LSM represents the standard model

Lagrangian, 𝑊





𝐵



 represents the gauge group

SU(2)L (U(1)Y) field strength tensor, D denotes the

covariant derivative, while m represents the WIMP's

mass. The scattering cross-section, crucial for

detection, can be calculated using these interactions,

often focusing on spin-independent or spin-

dependent interactions depending on the experiment

(Fukuda, 2024).

There are several methods for detection:

 Direct Detection. Measures the recoil energy of

nuclei after scattering with WIMPs. Key

principles include:

 Elastic Scattering. WIMPs elastically scatter off

target nuclei, transferring kinetic energy.

 Threshold Energy. Detectors are sensitive to

specific recoil energy thresholds to distinguish

WIMP interactions from background noise

(Fukuda, 2024).

 Indirect Detection. Searches for WIMP

annihilation or decay products, such as

neutrinos, gamma rays, or positrons.

 Cosmic Ray Observations. Observatories

monitor excesses in cosmic rays which may

indicate WIMP annihilation.

 Neutrino Telescopes. Detect neutrinos from the

Sun's or Earth's WIMP annihilations (Fukuda,

2024).

 Collider Searches. Producing WIMPs in high-

energy collisions, inferred by missing

transverse energy (MET).

 Mono-jet and Mono-photon Channels.

Characterized by a single high-energy jet or

photon and large MET, indicative of WIMPs

escaping detection (Fukuda, 2024).

Typical detectors are as follows:

TREX-DM. Using a high-pressure gas TPC with

Micromegas readout for detecting low-mass WIMPs.

Operated at the Canfranc Underground Laboratory, it

aims to achieve low background levels and energy

thresholds (Castel, 2024; Fukuda, 2024).

XENON1T. A liquid xenon detector designed for

ultra-low background levels, searching for WIMP-

induced nuclear recoils.

LUX-ZEPLIN (LZ). Another liquid xenon detector,

an upgrade from LUX, with improved sensitivity to

WIMP interactions (Fukuda, 2024).

The TREX-DM experiment has achieved significant

milestones in WIMP detection. The detector, with an

active volume filled with argon or neon mixtures,

demonstrated the ability to attain an 80 counts

ke 𝑉



𝑘𝑔



𝑑𝑎𝑦



background level and a low

energy threshold of 1 keVee. Recent developments

include a new readout plane integrating GEM and

Micromegas technologies with the goal of achieve

single-electron ionization energy thresholds. These

developments set up TREX-DM to investigate WIMP

masses lower than 1 GeV/c

. Future muon colliders

offer promising prospects for WIMP detection

through both direct and indirect methods. Indirect

detection benefits from analyzing the elastic µ+µ+

scattering's angular distribution, with beam

polarization enhancing sensitivity. Studies indicate

that with sufficient luminosity and beam polarization,

these colliders could probe thermal WIMP masses,

including the 2.7 TeV wino and 1 TeV Higgsino,

highlighting their potential in improving the

comprehension of DM (Fukuda, 2024). Fig. 2

demonstrates how the scattering cross-section's

angular distribution is impacted by the WIMP, with

polarization enhancing detection sensitivity.

Figure 2: Δ(θ) for various WIMP candidates

(Higgsino, Wino, 5-plet minimal dark matter) at

sqrt(s) = 10 TeV. The solid and dashed lines represent

unpolarized and polarized (Pµ+ = 0.8) initial muons,

respectively (Fukuda, 2024).

Searching Dark Matter Candidate Based on the State-of-Art Facilities: Evidence from WIMPs and ALPs

279

5 SEARCHING FOR OTHER

TYPES

Sterile neutrinos are hypothetical neutrinos that

interact without using the weak force, making them

hard to detect. They could have been created in the

early universe by oscillations from active neutrinos.

Their interactions can be represented by Feynman

diagrams showing the transition from active to sterile

neutrinos and vice versa (Akerib, 2020). The LZ

experiment is a state-of-the-art direct detection search

for WIMPs DM. It is a successor to the LUX and

ZEPLIN-III experiments and is designed to explore

WIMP-nucleon interactions with unprecedented

sensitivity.

WIMPs are hypothesized to interact with ordinary

matter through weak nuclear forces. These

interactions can be described using Feynman

diagrams, which depict the WIMP interacting with a

nucleon through the mediator particle's exchange,

such as a Z boson. The SI WIMP-nucleon cross-

section is a crucial element for characterizing these

interactions. The LZ experiment has set stringent

limits on this cross-section, particularly rejecting

values above 9.2 × 10



𝑐𝑚



at a 36GeV/cm

WIMP mass with 90% confidence (Aalbers, 2023).

The LZ detector employs a dual-phase xenon TPC to

search the characteristic low-energy nuclear recoils

(NR) caused by WIMP interactions. The TPC is

protected by a 4300-meter-water-equivalent

overburden at the SURF in Lead, South Dakota

(Aalbers, 2023). The detection process involves two

primary signals:

 Scintillation Light (S1): Prompt photons

produced by the interaction.

 Ionization Electrons (S2): Electrons freed from

xenon atoms, which drift to the liquid-gas

interface and generate secondary scintillation in

the gas phase.

It is possible to distinguish between NR and ER

using the ratio of S2 to S1, the latter being mainly due

to background radiation (Aalbers,2023) (Akerib,

2020). The LZ TPC is a cylindrical chamber with a

diameter and height of around 1.5 meters, filled by10

tonnes of liquid xenon. It is monitored by the top and

bottom of the chamber are equipped with arrays of

494 PMTs to detect S1 and S2 signals (Aalbers, 2023).

To reduce background noise, the TPC is encircled by

two additional detectors. A liquid xenon "skin"

detector between the cryostat wall and the TPC,

comprising 38 2-inch and 93 1-inch PMTs. An outer

detector comprising 17 tons of liquid scintillator filled

with gadolinium to absorb neutrons (Aalbers, 2023;

Akerib, 2020).

In its first 60 live days of operation, LZ's search

data showed no significant WIMP signal, resulting in

increased upper bounds on the cross-sections of

WIMP-nucleon. The spin-independent WIMP-

nucleon cross-section was given the strictest

constraint, particularly for a WIMP mass of 36

GeV/𝑐𝑚



(Aalbers,2023). The following plot from

the experiment illustrates the spin-independent

WIMP cross-section vs WIMP mass with a 90%

confidence level as depicted in Fig. 3. The LUX-

ZEPLIN experiment signifies a significant milestone

in DM research. By utilizing advanced detection

methods and sophisticated instrumentation, it has

achieved remarkable sensitivity in probing WIMP

interactions, setting stringent limits on their possible

cross-sections. These efforts contribute to narrowing

down the parameter space for WIMPs and guide

future explorations in the quest to understand DM.

Figure 3: The WIMP cross-section's upper limit

(black line), where the 1σ and 2σ sensitivity bands are

indicated, respectively, by the green and yellow bands.

(Aalbers, 2023).

6 LIMITATIONS AND

PROSPECTS

Despite significant advances, DM research faces

several limitations. One primary challenge is the

absence of direct detection, even with highly sensitive

experiments such as TREX-DM and LUX-ZEPLIN.

These experiments have only been able to set upper

limits on interaction cross-sections, indicating the

need for even more sensitive detectors and innovative

techniques to reduce background noise and lower

energy thresholds. Theoretical uncertainties further

complicate the search for DM. The vast parameter

space of potential DM particle masses and interaction

strengths means that current experiments may not be

probing the correct ranges. This ambiguity makes it

IAMPA 2024 - International Conference on Innovations in Applied Mathematics, Physics and Astronomy

280

challenging to design experiments that are both

comprehensive and sufficiently sensitive.

Despite these challenges, the prospects for DM

research are promising. Future experiments, such as

upgrades to existing detectors like LUX-ZEPLIN and

ADMX, aim to enhance sensitivity and explore new

parameter spaces. Innovations in detector technology,

including novel materials and quantum sensing

techniques, hold potential for breakthroughs in both

WIMP and axion searches. Interdisciplinary

collaborations and the integration of theoretical and

experimental efforts are expected to accelerate

progress. Advances in computational techniques,

particularly machine learning, can help analyze vast

datasets to identify potential DM signals amidst

background noise. Theoretical advancements in

understanding particle interactions and cosmological

implications will guide future experimental designs.

International collaborations will be crucial in

overcoming financial and technological barriers.

Projects like the Large Hadron Collider (LHC) and

future muon colliders offer complementary

approaches to DM research, potentially providing

indirect evidence through particle collisions and

decay signatures.

In summary, while DM research faces significant

limitations, ongoing technological advancements,

interdisciplinary efforts, and international

collaborations provide a hopeful outlook for future

discoveries. By continuing to push the frontiers of

detection capabilities and exploring novel theoretical

models, the scientific community is poised to make

significant strides in comprehending DM.

7 CONCLUSIONS

In summary, DM remains one of the biggest puzzles

in contemporary cosmology and astrophysics. This

study has provided a comprehensive overview of DM

research, concentrating on the leading candidates,

WIMPs and axions. It detailed their theoretical

underpinnings, detection methods, and recent

experimental advancements. Despite extensive

efforts, direct detection has not been achieved,

underscoring the challenges posed by DM's elusive

nature. However, significant progress has been made

in setting stringent limits on interaction cross-sections

and improving detection sensitivity. Looking forward,

the prospects for DM research are promising. Future

experiments, technological innovations, and

interdisciplinary collaborations are expected to

enhance sensitivity and explore new parameter spaces,

bringing us closer to a potential breakthrough. The

research's significance rests in its capacity to reveal

fundamental aspects of the universe's composition

and evolution. A thorough understanding of DM is

essential to understanding cosmic history, making

this research essential for advancing the knowledge

of the universe and guiding future explorations in the

quest to comprehend DM.

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