ULTRAMAN: A Proposed ultrasound detector for macroscopic dark matter

summary

The gist

The gist: ULTRAMAN proposes a passive ultrasound array experiment to search for macroscopic dark matter by detecting coherent acoustic disturbances generated as compact objects traverse a controlled

In short

ULTRAMAN proposes a passive ultrasound array experiment to find macroscopic dark matter by detecting coherent acoustic disturbances from compact objects passing through a target medium. The method reconstructs individual trajectories using synchronized, multielement arrays, searching for correlated multichannel tracks consistent with a single passage. Null results will constrain the mass and abundance of these objects.

Key concepts

Macroscopic Dark Matter (Macros): These are broad dark matter candidates like nuclear density objects or primordial black holes that are much heavier than typical particle dark matter. They are characterized by a mass (Mx) and an interaction cross-section (sigmaX) with ordinary matter, and ULTRAMAN aims to detect their passage.
Stopping Power (Sx): This is the energy deposited by a macroscopic dark matter object per unit of distance it travels through the target material. It is a key quantity that determines the strength of the acoustic disturbance caused by an individual passage, linking particle physics properties to measurable acoustic signals.
Acoustic Observable Space: This refers to the space defined by measured acoustic pressure and timing data from multiple ultrasound elements. A genuine dark matter event should appear as a correlated track in this space, distinct from random noise or single-element spikes, allowing for discrimination between different macro candidates.

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This episode discusses

The paper

ULTRAMAN: A Proposed ultrasound detector for macroscopic dark matter · Read on arXiv

Oem Trivedi, Robert J Scherrer, Alfredo Gurrola

Vanderbilt University

We propose ULTRAMAN (ULTRAsound Macro ANalyzer), a passive ultrasound array experiment designed to search for macroscopic dark matter (macros) through coherent acoustic disturbances generated as compact objects traverse a controlled target medium. Unlike existing dark matter detectors that primarily rely on scintillation, ionization, or other signatures of energy deposition, ULTRAMAN exploits the acoustic response of matter to reconstruct individual highly supersonic trajectories using synchronized multielement ultrasound arrays. The framework connects macro stopping power and interaction cross section to the resulting acoustic pressure, while the expected event rate probes the macro mass and abundance. A genuine candidate would appear not as an isolated radio frequency spike, but as a correlated multichannel track consistent with a single highly supersonic passage through the target. Representative macro, nuclearite, axion quark nugget, and primordial black hole benchmarks are shown to occupy distinct regions of the resulting acoustic observable space. Existing ultrasound technology offers a realistic route to an event-level terrestrial search for macroscopic dark matter, with null observations translating into complementary constraints on its parameter space.

Transcript

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: We're looking at the paper: "ULTRAMAN: A Proposed ultrasound detector for macroscopic dark matter".

Jocelyn: Here's the gist of the paper. ULTRAMAN proposes a passive ultrasound array experiment to search for macroscopic dark matter by detecting coherent acoustic disturbances generated as compact objects traverse a controlled target medium.

Vera: Macroscopic dark matter represents a broad class of dark matter candidates organized into compact objects (macros) with masses far above the conventional particle dark matter scale, such as nuclear density objects or primordial black holes Such objects are commonly characterized by a mass MX and an effective interaction cross section σX with ordinary matter.

Jocelyn: The framework connects macro stopping power and interaction cross section to the resulting acoustic pressure, while the expected event rate probes the macro mass and abundance.

Vera: Terrestrial matter itself may perhaps be used as a controlled target for detecting macroscopic dark matter.

Paper summary: Vera: So, to wrap up what this paper is proposing, ULTRAMAN sets out to search for macroscopic dark matter by looking for specific acoustic signatures generated when these compact objects pass through a controlled target medium.

Jocelyn: The core idea hinges on using a synchronized multielement ultrasound array in passive mode to listen for these spontaneous acoustic disturbances and record the raw radio frequency response from each element with precise timing.

Subrahmanyan: They are focusing on the geometric energy deposition framework developed by Sidhu, Scherrer, and Starkman because they see it as particularly well-matched to the physics of macro dark matter energy deposition compared to methods like magnetic resonance imaging or computed tomography.

Vera: That means they are emphasizing that ultrasound directly measures pressure disturbances propagating through matter, which is a key advantage here.

Jocelyn: They discuss the choice of target material, saying degassed water is arguably the cleanest primary choice because its density and sound speed are known precisely, and it has relatively low attenuation.

Subrahmanyan: They also mention polyvinyl alcohol or PVA as an attractive solid tissue mimicker because it's mechanically durable, though they note that gelatin might be better for early calibration because of potential long-term changes with time.

Vera: The theoretical framework connects the macro stopping power and interaction cross section to the resulting acoustic pressure, showing a characteristic scaling relationship where pi is proportional to vX times the square root of sigmaX.

Jocelyn: They also discuss how an expected event rate probes both the macro mass and its abundance, which is useful for setting constraints on what kind of object we are looking for.

Conclusion: Vera: Looking at this paper's title, "ULTRAMAN: A Proposed ultrasound detector for macroscopic dark matter," it really tells you the whole goal here is to use this specific acoustic detection method to find those large, compact dark matter candidates.

Jocelyn: The authors are suggesting that while existing detectors look for different things like ionization or scintillation, ULTRAMAN offers a way to search through coherent acoustic disturbances generated by objects traversing the target.

Subrahmanyan: The implication is that this experiment could provide an event-level terrestrial search capability for macroscopic dark matter, and null results from ULTRAMAN would actually give complementary constraints on the possible mass and abundance of these objects.

Vera: It's about moving beyond just looking for energy deposition and instead focusing on reconstructing a specific multichannel track consistent with one highly supersonic passage through the target medium.

Jocelyn: They stress that a compelling case for finding something would require seeing that same class of coherent multichannel event reconstructed across independent arrays, perhaps even across different target media, with a common trajectory and velocity.

Subrahmanyan: The apparatus they propose is modular, which makes it easier to reproduce and potentially run installations at different labs without needing the massive infrastructure of a large marine observatory.

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