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Hints of an Extra Dimension from DESI’s
Latest View of Dark Energy

Latest results from the Dark Energy Spectroscopic Instrument (DESI) suggest that dark energy (DE) may be decaying with time rather than remaining constant. DESI’s second data release (DR2), the most precise measurement yet of cosmic expansion, points to models in which the density of DE gradually evolves as the Universe expands.

In a recent study, Swagat S. Mishra, Varun Sahni, and collaborators William L. Matthewson, Arman Shafieloo and Yuri Shtanov show that this behaviour arises naturally if dark energy originates from a simple scalar field, instead of a fixed cosmological constant, in the higher-dimensional braneworld framework. Such a framework provides an excellent fit to DESI DR2 data alongside observations from Type Ia supernovae and the cosmic microwave background (CMB). In the braneworld scenario, our 3+1-dimensional Universe is viewed as a membrane (brane) embedded in a larger 4+1-dimensional space. This framework, pioneered by Varun Sahni and Yuri Shtanov in the early 2000s, now gains fresh motivation from DESI’s findings — offering a tantalizing hint that extra dimensions may subtly influence cosmic expansion.

Scientific Context and Importance

Released in March 2025, DESI DR2 provides the most precise mapping yet of the Universe’s expansion history. The data indicate that the DE equation-of-state parameter, w(z), evolves with time — favouring models where DE is phantom-like (w < –1) in the past, beyond redshift z ≈ 0.5, while it becomes quintessence-like (w > –1) at lower redshifts, closer to the present epoch. This behaviour suggests a decaying phantom dark energy, whose density initially grows before beginning to diminish with the expansion of the Universe. Following the DESI DR2 release, there has been a worldwide effort to theoretically understand this observationally inferred behaviour of decaying phantom dark energy.

Mishra, Sahni, and collaborators analysed a wide class of scalar-field potentials — quadratic, quartic, axion-like, exponential, and symmetry-breaking — and showed that they naturally reproduce this trend without invoking ghost instabilities or future singularities. In the braneworld framework, such scalar-field behaviour arises from higher-dimensional dynamics, where our 3+1-dimensional Universe is a brane evolving within a 4+1-dimensional bulk spacetime. This picture provides a simple, unified explanation of DESI’s results and hints that extra dimensions may leave subtle, observable traces in the cosmic expansion. If confirmed by future data, these findings would have far-reaching implications — for the nature of dark energy, the fate of the Universe, and the fundamental structure of space and time.

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[ DESI DR2 Galaxy Survey, The joint DESI + CMB + SN contours in (w0, wa) CPL parameter space, Evolution of Dark Energy ]


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[ Illustration: 3+1D brane (our Universe) embedded in a higher-dimensional bulk, DE Potentials, DE Evolution in the Braneworld ]

Quote

“DESI's latest observations suggest that dark energy could be dynamic - initially growing and then decaying with time – rather than being a simple cosmological constant. Such decaying phantom behaviour fits naturally within a model where dark energy arises from a scalar field propagating a higher-dimensional Braneworld - offering a possible glimpse of extra dimensions shaping cosmic evolution.”

- Swagat Mishra (University of Nottingham) & Varun Sahni (IUCAA)

Publication Details

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References


Research contacts:

Dr. Swagat Mishra Dr. Swagat S. Mishra
School of Physics and Astronomy,
University of Nottingham, United Kingdom

E-mail: Swagat.Mishra_at_nottingham.ac.uk
Prof. Varun Sahni Prof. Varun Sahni
IUCAA, Pune


E-mail: varun_at_iucaa.in
* please change _at_ to @