Relativistic Dispersion Spectra across Lorentz boosted frames: Spurious modes and the enigma of causality

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Hauptverfasser: Bhattacharyya, Sayantani, Mitra, Sukanya, Roy, Shuvayu, Singh, Rajeev
Format: Preprint
Veröffentlicht: 2025
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author Bhattacharyya, Sayantani
Mitra, Sukanya
Roy, Shuvayu
Singh, Rajeev
author_facet Bhattacharyya, Sayantani
Mitra, Sukanya
Roy, Shuvayu
Singh, Rajeev
contents The analysis of excitation spectra in gradient-expanded relativistic fluid theories frequently leads to pathologies under Lorentz boosts. However, extracting the dispersion modes in a Lorentz boosted inertial frame can be nontrivial. Motivated by this problem, we develop a general framework for deriving the linearized dispersion spectra in Lorentz boosted frames using only information from the local rest-frame dispersion structure, particularly its mode-expansion coefficients. We observe that, under a Lorentz transformation from the local rest frame, additional boosted solutions may appear that conflict with the causality of the theory; we refer to these as "spurious modes." The key developments presented here are: (i) a convenient method for obtaining dispersion spectra across inertial frames, bypassing the traditional procedure of solving the boosted polynomial, and (ii) the establishment of a direct connection between mode conservation and the causality of a theory, supported by a detailed proof.
format Preprint
id arxiv_https___arxiv_org_abs_2512_12450
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Relativistic Dispersion Spectra across Lorentz boosted frames: Spurious modes and the enigma of causality
Bhattacharyya, Sayantani
Mitra, Sukanya
Roy, Shuvayu
Singh, Rajeev
High Energy Physics - Theory
General Relativity and Quantum Cosmology
High Energy Physics - Phenomenology
Nuclear Theory
The analysis of excitation spectra in gradient-expanded relativistic fluid theories frequently leads to pathologies under Lorentz boosts. However, extracting the dispersion modes in a Lorentz boosted inertial frame can be nontrivial. Motivated by this problem, we develop a general framework for deriving the linearized dispersion spectra in Lorentz boosted frames using only information from the local rest-frame dispersion structure, particularly its mode-expansion coefficients. We observe that, under a Lorentz transformation from the local rest frame, additional boosted solutions may appear that conflict with the causality of the theory; we refer to these as "spurious modes." The key developments presented here are: (i) a convenient method for obtaining dispersion spectra across inertial frames, bypassing the traditional procedure of solving the boosted polynomial, and (ii) the establishment of a direct connection between mode conservation and the causality of a theory, supported by a detailed proof.
title Relativistic Dispersion Spectra across Lorentz boosted frames: Spurious modes and the enigma of causality
topic High Energy Physics - Theory
General Relativity and Quantum Cosmology
High Energy Physics - Phenomenology
Nuclear Theory
url https://arxiv.org/abs/2512.12450