Quintom scenario

In this scenario, the equation of state (EoS) $\backslash omega\; =\; p/\backslash rho$ of the dark energy, relating its pressure and energy density, can cross the boundary $\backslash omega\; =\; -1$ associated with the cosmological constant. The boundary separates the phantom-energy-like behavior with from the quintessence-like behavior with $\backslash omega\; >\; -1$.

According to a no-go theorem, a single-field, single-fluid scalar model cannot cross $\backslash omega\; =\; -1$. Achieving such a crossing requires at least two degrees of freedom in dark energy models built from ideal fluids or scalar fields. To allow the effective equation of state to cross $-1$, possible approaches include:

• Multiple fields & extra degrees of freedom, e.g. additional scalar fields or fermion fields;
• Higher-order derivative terms, e.g. Galileon theory;
• Modified gravities, e.g. $f(R)$, $f(T)$, $f(Q)$ gravity, metric-affine theory, or Horndeski gravity;
• Matter-dark energy interactions, e.g. interacting dark sector;
• Extra dimension effects, e.g. DGP gravity.

The Quintom scenario was applied in 2008 to produce a model of inflationary cosmology with a Big Bounce instead of a Big Bang singularity.

Current cosmological observations have given a clue in favor of the Quintom scenario. Since 2024, DESI has released the first year data and provided a possible "Quintom-B" scenario,{{cite arXiv | eprint=2504.06118 | title=Dynamical Dark Energy in light of the DESI DR2 Baryonic Acoustic Oscillations Measurements | last1=Gu | first1=Gan | last2=Wang | first2=Xiaoma | last3=Wang | first3=Yuting | last4=Zhao | first4=Gong-Bo | last5=Pogosian | first5=Levon | last6=Koyama | first6=Kazuya | last7=Peacock | first7=John A. | last8=Cai | first8=Zheng | last9=Cervantes-Cota | first9=Jorge L. | last10=Zhao | first10=Ruiyang | last11=Ahlen | first11=Steven | last12=Bianchi | first12=Davide | last13=Brooks | first13=David | last14=Claybaugh | first14=Todd | last15=Cole | first15=Shaun | last16=de la Macorra | first16=Axel | last17=De Mattia | first17=Arnaud | last18=Doel | first18=Peter | last19=Ferraro | first19=Simone | last20=Forero-Romero | first20=Jaime E. | last21=Gaztañaga | first21=Enrique | last22=Gontcho | first22=Satya Gontcho A. | last23=Gutierrez | first23=Gaston | last24=Hahn | first24=Changhoon | last25=Howlett | first25=Cullan | last26=Ishak | first26=Mustapha | last27=Kehoe | first27=Robert | last28=Kirkby | first28=David | last29=Kneib | first29=Jean-Paul | last30=Lahav | first30=Ofer | date=2025 | display-authors=1 }} with the equation of state crossing the boundary from below to above.{{Cite journal|author1=DESI Collaboration |title=DESI 2024 VI: Cosmological constraints from the measurements of baryon acoustic oscillations |date=2024-11-04 |arxiv=2404.03002 |last2=Adame |first2=A. G. |last3=Aguilar |first3=J. |last4=Ahlen |first4=S. |last5=Alam |first5=S. |last6=Alexander |first6=D. M. |last7=Alvarez |first7=M. |last8=Alves |first8=O. |last9=Anand |first9=A.|journal=Journal of Cosmology and Astroparticle Physics |volume=2025 |issue=2 |page=021 |doi=10.1088/1475-7516/2025/02/021 }} The DESI data release 2 shows a deviation from the ΛCDM model compared with dynamical dark energy, preferring a Quintom-B behavior crossing $\backslash omega\; =\; -1$ from below to above. {{cite arXiv |eprint=2503.14738 |class=astro-ph.CO |first1=DESI |last1=Collaboration |first2=M. |last2=Abdul-Karim |title=DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints |date=2025 |last3=Aguilar |first3=J. |last4=Ahlen |first4=S. |last5=Alam |first5=S. |last6=Allen |first6=L. |last7=Allende Prieto |first7=C. |last8=Alves |first8=O. |last9=Anand |first9=A. |last10=Andrade |first10=U. |last11=Armengaud |first11=E. |last12=Aviles |first12=A. |last13=Bailey |first13=S. |last14=Baltay |first14=C. |last15=Bansal |first15=P. |last16=Bault |first16=A. |last17=Behera |first17=J. |last18=BenZvi |first18=S. |last19=Bianchi |first19=D. |last20=Blake |first20=C. |last21=Brieden |first21=S. |last22=Brodzeller |first22=A. |last23=Brooks |first23=D. |last24=Buckley-Geer |first24=E. |last25=Burtin |first25=E. |last26=Calderon |first26=R. |last27=Canning |first27=R. |last28=Carnero Rosell |first28=A. |last29=Carrilho |first29=P. |last30=Casas |first30=L. |display-authors=1}}

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Category:Dark energy

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fr:Énergie fantôme

it:Energia fantasma