Analysis of Dark Matter: Invisible Foundation of Cosmic Structure

Tianfu Sun

Malvern college Qingdao, Qingdao, China

Keywords: Dark Matter, Cosmology, WIMPs, Axions, Galactic Dynamics.

Abstract: As a matter of fact, dark matter plays a key role in cosmology. This study presents a comprehensive

examination of dark matter, the mysterious substance that constitutes approximately 27% of the universe's

total mass-energy content. This research summarizes the historical development of dark matter theory,

beginning with early observational evidence and progressing to contemporary detection efforts. The paper

analyses multiple lines of evidence supporting dark matter's existence, including galactic rotation curves,

gravitational lensing effects, cosmic microwave background measurements, and large-scale structure

formation. One evaluates leading theoretical candidates such as Weakly Interacting Massive Particles

(WIMPs), axions, and sterile neutrinos, discussing their respective strengths and challenges. Current detection

methodologies are examined in detail, encompassing direct detection experiments, indirect observation

techniques, and collider-based searches. This study concludes with an assessment of future research directions

and the potential implications of dark matter discovery for particle physics and cosmology.

1 INTRODUCTION

The composition of the universe presents one of the

most profound mysteries in modern science.

Astronomical observations consistently demonstrate

that the visible matter comprising stars, planets, and

interstellar gas accounts for merely 5% of the total

cosmic mass-energy budget. The remaining 95%

consists of two enigmatic components: dark energy

(68%) and dark matter (27%). While dark energy

drives the accelerating expansion of the universe,

dark matter serves as the invisible scaffolding that

shapes cosmic structure on all scales (Bertone, 2010;

Bertone, G., Hooper, D., 2018).

The concept of dark matter emerged from early

20th century astronomical observations that revealed

discrepancies between visible mass and gravitational

effects. Swiss astronomer Fritz Zwicky first

postulated the existence of "dunkle Materie" (dark

matter) in 1933 when studying the Coma galaxy

cluster. His measurements of galactic velocities

indicated nearly ten times more mass than could be

accounted for by luminous matter alone. This

revolutionary idea gained substantial support in the

1970s through Vera Rubin's meticulous work on

galactic rotation curves, which demonstrated that

stars orbit galactic centres at velocities inconsistent

with Newtonian predictions based on visible mass.

Modern cosmology incorporates dark matter as a

fundamental component of the ΛCDM (Lambda Cold

Dark Matter) model, currently the most successful

framework for understanding cosmic evolution. This

model accurately predicts observed features of the

cosmic microwave background, large-scale structure

distribution, and galactic dynamics. However, despite

overwhelming indirect evidence for dark matter's

gravitational influence, its fundamental nature

remains unknown. The identification of dark matter's

particle properties represents one of the most pressing

challenges in contemporary physics, with profound

implications for the understanding of the universe (de

Swart, et al., 2017; Rubin, 2004).

This paper systematically examines the evidence

for dark matter, evaluates leading theoretical

candidates, reviews detection methodologies, and

discusses future research directions. By synthesizing

observational data, theoretical models, and

experimental results, one aims to provide a

comprehensive overview of current knowledge and

outstanding questions in dark matter research.

2 HISTORICAL DEVELOPMENT

OF DARK MATTER THEORY

The historical trajectory of dark matter research

reveals how astronomical observations progressively

Sun, T.

Analysis of Dark Matter: Invisible Foundation of Cosmic Structure.

DOI: 10.5220/0013834400004708

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 615-619

ISBN: 978-989-758-774-0

615

forced scientists to confront the limitations of visible

matter explanations. The earliest indications emerged

from studies of galactic motion in the 1930s. Fritz

Zwicky's analysis of the Coma Cluster using the virial

theorem showed that the cluster's mass-to-light ratio

exceeded expectations by an order of magnitude. His

conclusion that "dark matter is present in much

greater amount than luminous matter" initially met

with scepticism, as alternative explanations involving

modified dynamics or measurement errors seemed

plausible.

The case for dark matter strengthened

considerably in the 1970s with Vera Rubin and Kent

Ford's systematic studies of galactic rotation curves.

Their observations of spiral galaxies revealed flat

rotation curves - stellar orbital velocities remained

constant rather than decreasing with radius as

predicted by Keplerian mechanics. This anomaly

suggested the presence of extended mass distributions

(dark matter halos) surrounding visible galactic disks.

Rubin's work demonstrated that dark matter was not

just a cluster-scale phenomenon but a fundamental

component of individual galaxies.

The 1980s saw the development of numerical

simulations incorporating dark matter, which

successfully reproduced the observed large-scale

structure of the universe. These simulations showed

that cold dark matter (slow-moving particles) could

explain the formation of galaxies and galaxy clusters

through hierarchical clustering. The cosmic

microwave background measurements by COBE in

1992 and subsequent missions provided further

compelling evidence, revealing density fluctuations

consistent with dark matter's gravitational influence

in the early universe.

Modern dark matter research has expanded into

multiple directions, including direct detection

experiments, particle collider searches, and

increasingly precise astronomical observations. The

persistent failure to detect dark matter particles has

led to vigorous debates about alternative theories, but

the preponderance of evidence continues to support

the existence of non-baryonic dark matter as the most

plausible explanation for numerous astronomical

observations.

3 OBSERVATIONAL EVIDENCES

FOR DARK MATTER

3.1 Galactic Rotation Curves

The study of galactic rotation curves provides some

of the most direct evidence for dark matter's existence.

In a system governed solely by visible mass, stars'

orbital velocities should follow a Keplerian decline

with increasing distance from the galactic centre.

However, observations of spiral galaxies consistently

show flat rotation curves - orbital velocities remain

approximately constant across large radial distances.

This phenomenon can be explained by postulating an

extended dark matter halo surrounding each galaxy.

The halo's mass distribution follows an

approximately isothermal profile, with density

decreasing as 1/r² at large radii. This configuration

produces a flat rotation curve because the enclosed

mass M(r) increases linearly with radius, maintaining

a constant v² = GM(r)/r relationship (Mayet, et al.,

2016).

Recent observations using HI gas tracing in the

outer regions of galaxies have extended rotation curve

measurements to unprecedented distances, in some

cases out to 100 kiloparsecs. These studies continue

to show no evidence of Keplerian decline, reinforcing

the need for dark matter halos. Notable examples

include:

⚫ The Andromeda galaxy (M31), where rotation

curve measurements extend to 38 kpc

⚫ NGC 3198, with a well-measured flat rotation

curve extending to 30 kpc

⚫ Ultra-diffuse galaxies, which exhibit extremely

high mass-to-light ratios

3.2 Gravitational Lensing

Einstein's theory of general relativity predicts that

massive objects distort spacetime, bending light from

background sources. This gravitational lensing effect

provides a powerful tool for mapping mass

distributions independent of luminosity. Strong

lensing (multiple images or Einstein rings) and weak

lensing (statistical distortions of background galaxies)

both reveal substantial mass concentrations not

accounted for by visible matter. The Bullet Cluster

(1E 0657-558) presents perhaps the most dramatic

demonstration of dark matter's existence. This system

consists of two colliding galaxy clusters where:

⚫ X-ray observations reveal hot gas (the majority

of baryonic matter) concentrated between the

clusters

⚫ Weak lensing reconstruction shows the mass

peaks displaced from the gas, following the

galaxy distributions

This spatial separation demonstrates that most of

the mass is non-interacting (dark matter), while the

gas experiences hydrodynamic drag. Similar

observations in other merging clusters (e.g., MACS

J0025.4-1222) reinforce this conclusion.

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3.3 Cosmic Microwave Background

Anisotropies

Precision measurements of the cosmic microwave

background (CMB) provide crucial evidence for dark

matter's existence and properties. The Planck

satellite's measurements of temperature and

polarization anisotropies reveal an angular power

spectrum that matches ΛCDM model predictions

with remarkable accuracy. Key features requiring

dark matter include:

⚫ The relative heights of acoustic peaks, which

indicate the relative densities of baryonic and

non-baryonic matter

⚫ The observed matter density parameter Ωm ≈

0.315, far exceeding the baryonic density Ωb ≈

0.049

⚫ The Silk damping tail at small angular scales,

which reflects photon diffusion in the early

universe

CMB measurements also constrain dark matter's

temperature (favoring cold over warm or hot dark

matter) and its lack of significant interactions with

photons or baryons.

3.4 Large-Scale Structure Formation

The observed distribution of galaxies in the universe

forms a cosmic web of filaments, voids, and clusters

that developed through gravitational instability.

Numerical simulations demonstrate that this structure

formation requires dark matter's additional

gravitational influence to:

⚫ Explain the rapid growth of density

perturbations in the early universe

⚫ Account for observed cluster masses and

galaxy velocities

⚫ Reproduce the measured power spectrum

of matter fluctuations.

The Baryon Acoustic Oscillation (BAO) feature

in galaxy correlation functions provides a standard

ruler that further constrains dark matter's role in

structure formation. Measurements from surveys like

SDSS and DES consistently favor ΛCDM predictions

incorporating dark matter.

4 THEORETICAL CANDIDATES

FOR DARK MATTER

4.1 Weakly Interacting Massive

Particles (WIMPs)

WIMPs represent the most extensively studied dark

matter candidate, with theoretical roots in

supersymmetry (SUSY). These particles would

(Roszkowski, et al., 2018):

⚫ Have masses between 10 GeV and 10 TeV

⚫ Interact through the weak nuclear force and

gravity

⚫ Naturally achieve the correct relic abundance

through thermal freeze-out

The "WIMP miracle" refers to the remarkable

coincidence that weak-scale particles freezing out in

the early universe would naturally leave a density

matching observed dark matter values. SUSY models

predict several potential WIMP candidates, including

the neutralino (a linear combination of super partners

to the photon, Z boson, and Higgs).

4.2 Axions

Axions emerge as a solution to the Strong CP

Problem in quantum chromodynamics (QCD). These

ultra-light particles would (Schumann, 2019; Tao,

2020):

⚫ Have masses between 10⁻⁶ and 10⁻³ eV

⚫ Interact extremely weakly with ordinary

matter

⚫ Be produced non-thermally in the early

universe

Axion dark matter would behave as a coherent

classical field rather than individual particles.

Detection efforts exploit their predicted coupling to

electromagnetism, searching for axion-photon

conversion in strong magnetic fields.

4.3 Sterile Neutrinos

Sterile neutrinos represent a minimal extension to the

Standard Model that could explain dark matter. These

particles would:

⚫ Have masses in the keV range

⚫ Mix weakly with active neutrinos

⚫ Be produced through neutrino oscillations or

other mechanisms

Sterile neutrino dark matter could potentially

explain observed X-ray emission lines through

radiative decay channels. However, stringent

constraints from X-ray observations and structure

formation have limited viable parameter space.

4.4 Alternative Candidates

Other theoretically motivated dark matter candidates

include:

⚫ Primordial black holes: Hypothetical black

holes formed in the early universe

Analysis of Dark Matter: Invisible Foundation of Cosmic Structure

617

⚫ Self-interacting dark matter: Proposed to

solve small-scale structure problems

⚫ -Q-balls: Non-topological solitons in

supersymmetric theories

⚫ Hidden sector particles: Dark matter

connected to additional gauge symmetries

Each candidate presents distinct experimental

signatures and challenges for detection.

5 DETECTION

METHODOLOGIES

5.1 Direct Detection Experiments

Direct detection efforts aim to observe dark matter

particles scattering off atomic nuclei in underground

detectors (Chadha-Day, et al., 2022; Semertzidis &

Youn, 2022). Key technologies include:

⚫ Cryogenic detectors (SuperCDMS,

CRESST): Measure phonon and

ionization signals at millikelvin

temperatures

⚫ Liquid noble gas detectors (XENONnT,

LUX-ZEPLIN, PandaX): Use xenon or

argon as target materials

⚫ Directional detectors (DM-TPC,

CYGNUS): Attempt to reconstruct

scattering direction

Current experiments have reached sensitivities to

WIMP-nucleon cross sections below 10⁻⁴⁶ cm²,

probing much of the theoretically favoured parameter

space.

5.2 Indirect Detection

Indirect methods search for products of dark matter

annihilation or decay, including:

⚫ Gamma rays (Fermi-LAT, H.E.S.S.,

MAGIC)

⚫ Neutrinos (IceCube, ANTARES)

⚫ Antimatter (AMS-02, PAMELA)

Notable excesses like the Galactic Center gamma-

ray excess remain potential (though controversial)

dark matter signals.

5.3 Collider Searches

High-energy colliders like the LHC can produce dark

matter particles through:

⚫ Missing energy signatures in monojet events

⚫ Displaced vertices from long-lived particles

⚫ Exotic Higgs decays

ATLAS and CMS experiments have placed

stringent constraints on various dark matter models.

5.4 Astrophysical Probes

Complementary astrophysical constraints come from:

⚫ Dwarf spheroidal galaxies (excellent targets

for indirect detection)

⚫ 21 cm cosmology (probes early universe

dark matter effects)

⚫ Stellar streams (sensitive to dark matter

substructure)

6 CURRENT CHALLENGES AND

FUTURE DIRECTIONS

Despite decades of increasingly sensitive searches, no

definitive dark matter detection has been made

(Bergström, 2012; Misiaszek, & Rossi, 2024). This

null result has led to several possible interpretations:

⚫ Dark matter particles may have properties

outside traditional search windows

⚫ The understanding of dark matter's

astrophysical distribution may be

incomplete

⚫ Alternative gravitational theories may need

reconsideration

Future directions include:

⚫ Next-generation detectors (DARWIN,

ARGO, ADMX-Gen2)

⚫ Novel detection concepts (quantum sensors,

nuclear clocks)

⚫ Multi-messenger astrophysics approaches

⚫ Continued theoretical development

The resolution of the dark matter problem will

undoubtedly require persistent experimental efforts

across multiple fronts, coupled with theoretical

innovation. Success would revolutionize the

understanding of fundamental physics and the

cosmos.

7 CONCLUSIONS

The enigma of dark matter stands as one of the most

significant unsolved problems in modern physics.

Extensive observational evidence from multiple

independent lines of inquiry consistently points to the

existence of non-baryonic dark matter as the most

plausible explanation for numerous astrophysical

phenomena. While the nature of dark matter remains

elusive, the convergence of evidence from galactic

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dynamics, gravitational lensing, cosmic microwave

background measurements, and large-scale structure

formation presents a compelling case for its existence.

Theoretical models have proposed various

candidates, with WIMPs and axions currently

representing the most promising possibilities.

Experimental efforts spanning direct detection,

indirect observation, and collider production have

dramatically advanced the understanding while

simultaneously revealing the complexity of the dark

matter problem. The continued null results have

prompted healthy scepticism and alternative

approaches, yet the preponderance of evidence

continues to support the dark matter paradigm.

Future research directions hold tremendous

promise for resolving this fundamental mystery.

Next-generation experiments with improved

sensitivity, novel detection techniques, and

innovative theoretical approaches may finally unveil

dark matter's true nature. Such a discovery would not

only solve one of cosmology's greatest puzzles but

would also open new frontiers in the understanding of

particle physics and the fundamental nature of the

universe.

As one stands at the frontier of this profound

scientific quest, the investigation of dark matter

continues to push the boundaries of human

knowledge, challenging the most fundamental

assumptions about the composition and evolution of

the cosmos. The solution to the dark matter problem

will undoubtedly rank among the most significant

scientific achievements of the time, with implications

reaching far beyond astrophysics into the very

foundations of physical law.

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