Is The Trace Anomaly at its Minimum Value at Neutron Star Centers?
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arXiv
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| Natura: | Preprint |
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2025
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| _version_ | 1866908748119801856 |
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| author | Cai, Bao-Jun Li, Bao-An Ma, Yu-Gang |
| author_facet | Cai, Bao-Jun Li, Bao-An Ma, Yu-Gang |
| contents | While the equation of state (EOS) $P(\varepsilon)$ of neutron star (NS) matter has been extensively studied, the EOS-parameter $ϕ= P/\varepsilon$ or equivalently the dimensionless trace anomaly $Δ= 1/3 - ϕ$, which quantifies the balance between pressure $P$ and energy density $\varepsilon$, remains far less explored, especially in NS cores. Its bounds and density profile carry crucial information about the nature of superdense matter. Physically, the EOS-parameter $ϕ$ represents the mean stiffness of matter accumulated from the stellar surface up to a given density. Based on the intrinsic structure of the Tolman--Oppenheimer--Volkoff equations, we show that $ϕ$ decreases monotonically outward from the NS center, independent of any specific input NS EOS model. Furthermore, observational evidence of a peak in the speed-of-sound squared (SSS) density-profile near the center effectively rules out a valley and a subsequent peak in the radial profile of $ϕ$ at similar densities, reinforcing its monotonic decrease. These model-independent relations impose strong constraints on the near-center behavior of the EOS-parameter $ϕ$, particularly demonstrating that the mean stiffness (or equivalently $Δ$) reaches a local maximum (minimum) at the center. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_03714 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Is The Trace Anomaly at its Minimum Value at Neutron Star Centers? Cai, Bao-Jun Li, Bao-An Ma, Yu-Gang High Energy Astrophysical Phenomena High Energy Physics - Phenomenology High Energy Physics - Theory Nuclear Experiment Nuclear Theory While the equation of state (EOS) $P(\varepsilon)$ of neutron star (NS) matter has been extensively studied, the EOS-parameter $ϕ= P/\varepsilon$ or equivalently the dimensionless trace anomaly $Δ= 1/3 - ϕ$, which quantifies the balance between pressure $P$ and energy density $\varepsilon$, remains far less explored, especially in NS cores. Its bounds and density profile carry crucial information about the nature of superdense matter. Physically, the EOS-parameter $ϕ$ represents the mean stiffness of matter accumulated from the stellar surface up to a given density. Based on the intrinsic structure of the Tolman--Oppenheimer--Volkoff equations, we show that $ϕ$ decreases monotonically outward from the NS center, independent of any specific input NS EOS model. Furthermore, observational evidence of a peak in the speed-of-sound squared (SSS) density-profile near the center effectively rules out a valley and a subsequent peak in the radial profile of $ϕ$ at similar densities, reinforcing its monotonic decrease. These model-independent relations impose strong constraints on the near-center behavior of the EOS-parameter $ϕ$, particularly demonstrating that the mean stiffness (or equivalently $Δ$) reaches a local maximum (minimum) at the center. |
| title | Is The Trace Anomaly at its Minimum Value at Neutron Star Centers? |
| topic | High Energy Astrophysical Phenomena High Energy Physics - Phenomenology High Energy Physics - Theory Nuclear Experiment Nuclear Theory |
| url | https://arxiv.org/abs/2511.03714 |