Applying the Viterbi Algorithm to Planetary-Mass Black Hole Searches

The search for subsolar mass primordial black holes (PBHs) poses achallenging problem due to the low signal-to-noise ratio, extended signalduration, and computational cost demands, compared to solar mass binary blackhole events. In this paper, we explore the possibility of investigating themass range between subsolar and planetary masses, which is not accessible usingstandard matched filtering and continuous wave searches. We propose asystematic approach employing the Viterbi algorithm, a dynamic programmingalgorithm that identifies the most likely sequence of hidden Markov statesgiven a sequence of observations, to detect signals from small mass PBHbinaries. We formulate the methodology, provide the optimal length forshort-time Fourier transforms, and estimate sensitivity. Subsequently, wedemonstrate the effectiveness of the Viterbi algorithm in identifying signalswithin mock data containing Gaussian noise. Our approach offers the primaryadvantage of being agnostic and computationally efficient.