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Cosmic acceleration in f(Q) gravity: a nonlinear equation of state approach.

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Title: Cosmic acceleration in f(Q) gravity: a nonlinear equation of state approach.
Authors: Özansoy, Mehmet1 (AUTHOR) ozansoy.mhmt@gmail.com, Shukla, Bhupendra Kumar2 (AUTHOR) bhupendrashukla695@gmail.com, Sofuoğlu, Değer3 (AUTHOR) degers@istanbul.edu.tr, Beesham, Aroonkumar4,5,6,7 (AUTHOR) abeesham@yahoo.com, Tripathi, Rajnee8 (AUTHOR) rajneetripathi@hotmail.com
Source: European Physical Journal C -- Particles & Fields. Feb2026, Vol. 86 Issue 2, p1-17. 17p.
Subjects: Equations of state, Expanding universe, Physical cosmology, Hubble constant, Markov chain Monte Carlo
Abstract: We investigate late-time cosmic acceleration within the framework of f(Q) gravity supplemented by a phenomenological nonlinear equation of state of the form p = A ρ - B ρ. Adopting a power-law ansatz f (Q) = γ , (Q / Q 0) n , we derive analytic expressions for the energy density and Hubble function and confront the model with a combined dataset consisting of CC, SNIa, BAO, quasar, and GRB observations covering 0.106 < z < 2.33. A Bayesian MCMC analysis constrains the parameter set H 0 , A , B , c , n and yields H 0 ≃ 71. 6 - 1.9 + 1.0 km s - 1 Mpc - 1 for the joint sample, together with a transition redshift z tr ≈ 0.68. Cosmographic diagnostics indicate a present-day deceleration parameter q 0 ≈ - 0.59 , with mild deviations of the jerk and snap parameters from their Λ CDM values at low redshift. Thermodynamic and causal consistency is ensured by the condition 0 ≤ c s 2 (z) ≤ 1 , while the matter-sector energy conditions remain satisfied up to z ∼ O (1). A statistical comparison with the concordance model shows that the proposed f (Q) + nEoS scenario achieves a goodness of fit comparable to Λ CDM over the same dataset, with χ 2 min model = 255.93 versus χ 2 min Λ CDM = 260.5 and χ red 2 ≈ 0.96 for both cases. The Akaike Information Criterion yields Δ AIC ≈ 1.4 , indicating statistical equivalence with a mild preference for Λ CDM due to its smaller parameter space. Therefore, the model provides a viable description of the late-time expansion history, allowing controlled deviations from Λ CDM that modestly alleviate, though do not resolve, the H 0 tension. Several other interesting properties of a nEoS are also elucidated upon. [ABSTRACT FROM AUTHOR]
Copyright of European Physical Journal C -- Particles & Fields is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Cosmic acceleration in f(Q) gravity: a nonlinear equation of state approach.
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  Data: &lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22&#214;zansoy%2C+Mehmet%22&quot;&gt;&#214;zansoy, Mehmet&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;i&gt; ozansoy.mhmt@gmail.com&lt;/i&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Shukla%2C+Bhupendra+Kumar%22&quot;&gt;Shukla, Bhupendra Kumar&lt;/searchLink&gt;&lt;relatesTo&gt;2&lt;/relatesTo&gt; (AUTHOR)&lt;i&gt; bhupendrashukla695@gmail.com&lt;/i&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Sofuoğlu%2C+Değer%22&quot;&gt;Sofuoğlu, Değer&lt;/searchLink&gt;&lt;relatesTo&gt;3&lt;/relatesTo&gt; (AUTHOR)&lt;i&gt; degers@istanbul.edu.tr&lt;/i&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Beesham%2C+Aroonkumar%22&quot;&gt;Beesham, Aroonkumar&lt;/searchLink&gt;&lt;relatesTo&gt;4,5,6,7&lt;/relatesTo&gt; (AUTHOR)&lt;i&gt; abeesham@yahoo.com&lt;/i&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Tripathi%2C+Rajnee%22&quot;&gt;Tripathi, Rajnee&lt;/searchLink&gt;&lt;relatesTo&gt;8&lt;/relatesTo&gt; (AUTHOR)&lt;i&gt; rajneetripathi@hotmail.com&lt;/i&gt;
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  Data: We investigate late-time cosmic acceleration within the framework of f(Q) gravity supplemented by a phenomenological nonlinear equation of state of the form p = A ρ - B ρ. Adopting a power-law ansatz f (Q) = γ , (Q / Q 0) n , we derive analytic expressions for the energy density and Hubble function and confront the model with a combined dataset consisting of CC, SNIa, BAO, quasar, and GRB observations covering 0.106 &lt; z &lt; 2.33. A Bayesian MCMC analysis constrains the parameter set H 0 , A , B , c , n and yields H 0 ≃ 71. 6 - 1.9 + 1.0 km s - 1 Mpc - 1 for the joint sample, together with a transition redshift z tr ≈ 0.68. Cosmographic diagnostics indicate a present-day deceleration parameter q 0 ≈ - 0.59 , with mild deviations of the jerk and snap parameters from their Λ CDM values at low redshift. Thermodynamic and causal consistency is ensured by the condition 0 ≤ c s 2 (z) ≤ 1 , while the matter-sector energy conditions remain satisfied up to z ∼ O (1). A statistical comparison with the concordance model shows that the proposed f (Q) + nEoS scenario achieves a goodness of fit comparable to Λ CDM over the same dataset, with χ 2 min model = 255.93 versus χ 2 min Λ CDM = 260.5 and χ red 2 ≈ 0.96 for both cases. The Akaike Information Criterion yields Δ AIC ≈ 1.4 , indicating statistical equivalence with a mild preference for Λ CDM due to its smaller parameter space. Therefore, the model provides a viable description of the late-time expansion history, allowing controlled deviations from Λ CDM that modestly alleviate, though do not resolve, the H 0 tension. Several other interesting properties of a nEoS are also elucidated upon. [ABSTRACT FROM AUTHOR]
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  Data: &lt;i&gt;Copyright of European Physical Journal C -- Particles &amp; Fields is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder&#39;s express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.&lt;/i&gt; (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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      – Type: doi
        Value: 10.1140/epjc/s10052-026-15310-1
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      – Code: eng
        Text: English
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        PageCount: 17
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    Subjects:
      – SubjectFull: Equations of state
        Type: general
      – SubjectFull: Expanding universe
        Type: general
      – SubjectFull: Physical cosmology
        Type: general
      – SubjectFull: Hubble constant
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      – SubjectFull: Markov chain Monte Carlo
        Type: general
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      – TitleFull: Cosmic acceleration in f(Q) gravity: a nonlinear equation of state approach.
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            NameFull: Özansoy, Mehmet
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            NameFull: Shukla, Bhupendra Kumar
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              Text: Feb2026
              Type: published
              Y: 2026
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