arXiv subjects

T. Toghrai

Publications and source records attributed to T. Toghrai.

2 recordsLinked to original sources

arXiv2026

Evaporation of Primordial Black Holes with Multimodal Mass and Extended Spin Distributions: Cosmological Imprints on the Effective Number of Relativistic Species

Primordial black holes (PBHs) form through several distinct mechanisms, each imprinting a characteristic mass function that a single-mass treatment risks erasing. Building on the FRISBHEE code, we introduce FRISHBEE, implementing four mass functions--log-normal, power-law, critical collapse, metric preheating--in a multimodal framework, with spin modeled via Gaussian and Fishbach profiles. Crucially, each channel's weight is derived from the primordial collapse probability rather than fitted, tying the mass function to the power-spectrum amplitude--a link between inflationary model-building and CMB observables. Solving the Friedmann-Boltzmann equations for $M_{\rm PBH}^{\rm in}=10^{7}$~g in the pre-BBN window, we compute $ΔN_{\rm eff}$ for five distributions, three spin configurations, and three weightings. Extended mass functions enhance $ΔN_{\rm eff}$ over the monochromatic benchmark by factors of $\sim\!1.03$ (critical collapse) to $\sim\!1.84$ (log-normal), preserving the hierarchy $LN > MM > PL > MP > CC$ across the mass window $\{10^{5},10^{7},10^{8}\}$~g. Near-extremal spin ($a_{\star}=0.99$) and spin-2 dark radiation invert this trend: superradiant spin loss averages away faster in broad distributions than in a monochromatic population, letting the monochromatic approximation overestimate $ΔN_{\rm eff}$. Against CMB-S4 and Simons Observatory sensitivities ($σ\simeq 0.06$ and $0.05$), the monochromatic benchmark is undetectable for scalar dark radiation (sDR $=0$), while log-normal, power-law, and multimodal distributions reach $\sim\!1.6$--$1.7σ$; for spin-2 dark radiation the signal drops over an order of magnitude, with none detectable. The formation channel thus governs the magnitude and observational accessibility of the Hawking signal, establishing $ΔN_{\rm eff}$ as a discriminant between single- and multi-channel PBH formation scenarios.

astro-ph.CO↗

arXiv2026

First-Law Entropy and a Degenerate Extremal Remnant in a Minimal-Length Simpson--Visser-Type Regular Black Hole: Geometrothermodynamics, Phase Structure, and Observational Discriminants

We construct the first-law-consistent entropy of a geometrically minimal-length-deformed Schwarzschild spacetime, obtained via the areal-radius substitution $R(r)=\sqrt{r^{2}+\ell^{2}}$ on $r\in[0,+\infty)$ with $f(R)=1-2M/R$, whose nonvanishing Einstein tensor sources an effective geometric fluid with no classical matter counterpart. Integrating the first law gives $S=π[r_{h}R_{h}+\ell^{2}\ln((r_{h}+R_{h})/\ell)]$. This coincides in functional form with the semiclassical term found independently by Joshi and Joshi, but we fix its boundary condition $S(r_h=0)=0$ on independent physical grounds and adopt it, rather than the Bekenstein--Hawking area law, as the complete entropy of the model, building the free energy, geometrothermodynamics, and mode-stability analysis on it. Evaporation, governed by the Helmholtz free energy $F(M)$, terminates at $M_{\min}=\ell/2$ in a previously unrecognised endpoint: a degenerate extremal regular black hole, where the regular centre coincides with a degenerate Killing horizon of quadratic order, $f\approx r^{2}/(2\ell^{2})$, at areal radius $\ell$, with $T_{H}\to 0$, $S\to 0$, $C\to 0^{+}$, and finite curvature everywhere; we display its Penrose--Carter structure for the first time. The same entropy, with $\ell$, defines the equilibrium state space of a Legendre-invariant geometrothermodynamic (GTD) description whose curvature scalar diverges independently at the Davies-type transition $M^{*}=\ell/\sqrt{2}$ and at $M_{\min}$, a divergence with no counterpart in the minimal-length black hole literature, specific to a genuine horizon at $S=0$. We embed this remnant within the observational discriminant noted qualitatively by Tsukamoto: exact shadow degeneracy combined with a measurable photon-ring flux enhancement $r_{n}=e^{-2π/a}>e^{-2π}$, accessible to next-generation very-long-baseline interferometry.

gr-qc↗