The initial-action branch of everpresent Lambda: an e-fold law, the exit, and what late acceleration would require

In the volume-based everpresent Lambda model of Das, Nasiri and Yazdi, the cosmological term is Lambda = (8 pi G S0 + fluctuations)/V, where V is the past light-cone four-volume and S0 an initial action. A recent no-go result (Güz, 2026) shows that the smooth 1/sqrt(V) branch with S0 = 0 cannot start acceleration on power-law backgrounds, and leaves the branches carrying a 1/V term uncovered. This note treats the smooth part of that S0 branch. Main results, using the first Friedmann equation (background-equivalent to the authors' Scheme 1): An exact reduction of the past-cone volume to ordinary differential equations. Dependence of the accelerated e-folds essentially only on u_i = 4 pi V_i/(3 kappa^2), with kappa = 8 pi G S0/3. An e-fold law N = 1/u_i + (13/6) ln(1/u_i) + c, where the coefficient 13/6 comes from the memory kernel of the past cone. An exit that freezes the expansion (a tends to a constant, V tends to pi t^4/3), with no reheating. w_eff = 1 + 2w for the S0 term in decelerating eras, and w_eff = 0.29 today on a LambdaCDM history. With Lambda(x0) set to today's Lambda, no acceleration before a = 30 unless the seed volume exceeds 1.55 times today's past-cone volume (about 5.8e242 in Planck units). The authors' Scheme 2 (the second Friedmann equation) is used as a cross-check. There the corresponding threshold is 0.48, but the Ahmed-Sorkin fictitious dust contributes substantially. The model's noise at alpha = 0.015 leaves the mean e-fold count unchanged within its error. Late acceleration from this branch therefore requires both the size of Lambda and a seed comparable to the observable past cone to be put in by hand. Code and all numbers are in the deposit.

Authors

Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-11-09
DOI
https://doi.org/10.5281/zenodo.24068858
Primary Topic
Cosmology and Gravitation Theories
Type
preprint
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preprint

The initial-action branch of everpresent Lambda: an e-fold law, the exit, and what late acceleration would require

Dat Tan Nguyen
Zenodo (CERN European Organization for Nuclear Research)
Cosmology and Gravitation Theories
preprint

The initial-action branch of everpresent Lambda: an e-fold law, the exit, and what late acceleration would require

Dat Tan Nguyen
preprint en

Abstract

In the volume-based everpresent Lambda model of Das, Nasiri and Yazdi, the cosmological term is Lambda = (8 pi G S0 + fluctuations)/V, where V is the past light-cone four-volume and S0 an initial action. A recent no-go result (Güz, 2026) shows that the smooth 1/sqrt(V) branch with S0 = 0 cannot start acceleration on power-law backgrounds, and leaves the branches carrying a 1/V term uncovered. This note treats the smooth part of that S0 branch. Main results, using the first Friedmann equation (background-equivalent to the authors' Scheme 1): An exact reduction of the past-cone volume to ordinary differential equations. Dependence of the accelerated e-folds essentially only on u_i = 4 pi V_i/(3 kappa^2), with kappa = 8 pi G S0/3. An e-fold law N = 1/u_i + (13/6) ln(1/u_i) + c, where the coefficient 13/6 comes from the memory kernel of the past cone. An exit that freezes the expansion (a tends to a constant, V tends to pi t^4/3), with no reheating. w_eff = 1 + 2w for the S0 term in decelerating eras, and w_eff = 0.29 today on a LambdaCDM history. With Lambda(x0) set to today's Lambda, no acceleration before a = 30 unless the seed volume exceeds 1.55 times today's past-cone volume (about 5.8e242 in Planck units). The authors' Scheme 2 (the second Friedmann equation) is used as a cross-check. There the corresponding threshold is 0.48, but the Ahmed-Sorkin fictitious dust contributes substantially. The model's noise at alpha = 0.015 leaves the mean e-fold count unchanged within its error. Late acceleration from this branch therefore requires both the size of Lambda and a seed comparable to the observable past cone to be put in by hand. Code and all numbers are in the deposit.

Zenodo (CERN European Organization for Nuclear Research)
Cosmology and Gravitation Theories
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