ULTRAMAN: A Proposed ultrasound detector for macroscopic dark matter

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 target medium.

Motivation and Target Selection

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. 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. Terrestrial matter itself may perhaps be used as a controlled target for detecting macroscopic dark matter. Modern medical and laboratory diagnostics already employ highly sensitive physical probes of matter, and it is natural to ask whether these instruments themselves could respond to the passage of a macro even when the deposited energy is far below the threshold required to produce appreciable biological damage. Ultrasound is particularly well matched to the physics of macro dark matter energy deposition because it directly measures pressure disturbances propagating through matter.

ULTRAMAN Experimental Setup

The ULTRAMAN setup consists of a controlled target volume surrounded on several sides by multielement ultrasound arrays operated predominantly in a passive receiving mode. Rather than transmitting conventional imaging pulses continuously, the arrays would listen for spontaneous acoustic disturbances originating inside the target and record the raw RF response of each element with synchronized timing. Arrays placed above, below and along the lateral faces of the target would allow the same disturbance to be observed from several directions, making it possible to reconstruct whether the signals are consistent with a single compact object traversing the volume. The choice of target material is equally important because the experiment requires a medium that is acoustically well characterized, stable over long periods and sufficiently homogeneous that unusual transients are not dominated by internal imperfections. Degassed water is arguably the cleanest primary choice because its density and sound speed are precisely known, its attenuation is relatively low, it can be produced in large volumes at modest cost and removal of dissolved gas substantially suppresses bubble related acoustic backgrounds. If a solid tissue mimicking target is preferred, polyvinyl alcohol (PVA) cryogel is also attractive because it is mechanically durable and its acoustic properties can be tuned to resemble soft tissues.

Theoretical Framework for Detection

The most convenient model independent quantity is the stopping power SX, defined as the energy deposited by a macroscopic dark matter object per unit path length through the target. For a path length L through a homogeneous target, the corresponding deposited energy is given by Eq. (2). The interaction cross section controls how strongly an individual passage perturbs the target, while the mass MX primarily determines how frequently such objects cross the detector. The acoustic energy registered by element i can then be written schematically as Eac,i = ηXGiEdep. The characteristic scaling is pi ∝ vX √ σX.

Observable Signatures and Discrimination

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. The timing structure probes the trajectory and velocity, while the acoustic intensity probes the interaction strength. The measured arrival times must admit a common solution for x0, vX and the passage time. Multiple array elements would also provide redundant determinations of these quantities and hence would be an important internal consistency test. An additional consistency test can be obtained by placing two independently instrumented target volumes in series, for example one containing degassed water and another containing gelatin or PVA. A compelling case would require the same class of coherent multichannel event to be reconstructed across independent arrays, preferably across more than one target medium, with a common trajectory, a Galactic scale velocity, a consistent stopping power and no plausible acoustic, mechanical or electronic background explanation.

Event Rate and Constraints

The expected rate through an effective directional projected search area Asearch is approximately ΓX = fXρDM MX vXAsearchϵX. The characteristic dependence ΓX ∝ M−1 X is especially useful, as the strength of an individual event is governed primarily by the stopping power, whereas its expected frequency carries information about the macro mass and abundance. A null result would hence constrain only the portion of (MX, σX) space for which both the acoustic response and the expected flux are sufficiently large. The rates displayed here are intended as a conservative illustration of this effect rather than a replacement for a full recasting of every existing limit. A null result over a calibrated exposure is also informative because it constrains only the region in which the experiment is demonstrably efficient, placing an upper bound on fX as a function of σX and MX.

Conclusion and Feasibility

ULTRAMAN is realistic within present laboratory technology, since multielement ultrasound arrays, synchronized RF acquisition, passive acoustic imaging and tissue mimicking or water based substances are all already routinely available. The main experimental challenge would not be the basic hardware but instead the ability to achieve sufficiently low acoustic and electronic backgrounds, stable long duration operation, and reliable calibration of the conversion between deposited energy and measured pressure. A first proof of principle experiment could be implemented using existing research ultrasound systems and a controlled water or PVA target, while a dedicated dark matter experiment would require larger target area and substantially longer exposure. Positive or null results from such controlled ULTRAMAN installations could consequently provide useful guidance for the interpretation, optimization and eventual motivation of much larger acoustic searches as well. The apparatus is also modular and considerably easier to reproduce, allowing multiple installations to be operated at different laboratories without the infrastructure required by a large marine observatory. The central observable for us is not just the existence of an acoustic pressure pulse, but a densely sampled channel-dependent timing pattern that must be consistent with one common retarded trajectory and Galactic scale velocity. A compelling case would require the same class of coherent multichannel event to be reconstructed across independent arrays, preferably across more than one target medium, with a common trajectory, a Galactic scale velocity, a consistent stopping power and no plausible acoustic, mechanical or electronic background explanation. A null result over a calibrated exposure is also informative because it constrains only the region in which the experiment is demonstrably efficient, placing an upper bound on fX as a function of σX and MX. The signature illustrated in Fig. 3 shows the coherent channel and time response expected for several representative macroscopic dark matter benchmarks. The existence of such a coherent multichannel feature, together with its reconstructed velocity and intensity, constitutes the primary event level signature through which the experiment could identify and subsequently discriminate macroscopic dark matter candidates. The paper concludes that a compelling case would require the same class of coherent multichannel event to be reconstructed across independent arrays, preferably across more than one target medium, with a common trajectory, a Galactic scale velocity, a consistent stopping power and no plausible acoustic, mechanical or electronic background explanation. The apparatus is also modular and considerably easier to reproduce, allowing multiple installations to be operated at different laboratories without the infrastructure required by a large marine observatory. The central observable for us is not just the existence of an acoustic pressure pulse, but a densely sampled channel-dependent timing pattern that must be consistent with one common retarded trajectory and Galactic scale velocity. A compelling case would require the same class of coherent multichannel event to be reconstructed across independent arrays, preferably across more than one target medium, with a common trajectory, a Galactic scale velocity, a consistent stopping power and no plausible acoustic, mechanical or electronic background explanation <ref:2610.

1. Improved AI system can perform event-level detection for macroscopic dark matter by analyzing multichannel track consistency rather than isolated RF spikes. This is achieved by reconstructing a common trajectory and velocity from correlated arrival times across multiple synchronized ultrasound array elements, which provides a substantially stronger signature than an isolated RF spike.

2. The AI system can estimate the stopping power of a macro using the measured pressure amplitude and known parameters by inverting the relationship: SX ≃ p squared i Aeff,i∆ti ηXGiρcsL and subsequently calculating the interaction cross section. This allows for direct probing of the interaction strength through acoustic intensity.

3. The AI system can discriminate between a genuine macro event and background noise by testing consistency across different target media using the relationship: SX,1 SX,2 = ρ1v 21 ρ2v 22 and checking if the reconstructed trajectory appears in both targets while the calibrated acoustic response changes consistently with the medium.

4. The AI system can predict the expected event rate of a macroscopic dark matter candidate by calculating Gamma X using: ΓX = fXρDM MX vXAsearchϵX, allowing it to map candidates onto an observable plane that explicitly considers both the stopping power trajectories and the directly observable acoustic parameter space.

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.