Noether charges and the first law of thermodynamics for multifractional Schwarzschild black hole in the q-derivative theory

TL;DR

This paper explores black-hole thermodynamics within multi-fractional q-derivative theory, revealing how profile parameters influence temperature and entropy, and proposing an extended first law incorporating these effects.

Contribution

It introduces a method to include multi-fractional profile parameters into black-hole thermodynamics, ensuring an integrable entropy functional and a consistent extended first law.

Findings

Canonical charges are profile-insensitive and follow the area law.

Temperature depends explicitly on the multi-fractional profile at the horizon.

An extended first law with additional work terms accounts for profile variations.

Abstract

In this paper, we investigate black-hole thermodynamics in the multi-fractional theory with $q$-derivatives, focusing on static, spherically symmetric vacuum solutions in the spherical-coordinate approximation. In the geometric frame the solution is exactly Schwarzschild in the areal radius $q$, so that canonical charges can be defined using standard covariant methods. The conserved mass depends only on the Schwarzschild integration constant, and the Iyer--Wald entropy satisfies the usual area law in terms of the geometric horizon radius. When the Hawking temperature is defined in the fractional radial coordinate $r$, however, it acquires an explicit dependence on the multi-fractional profile through the local factor $q'(r_{\rm h})$ at the horizon. As a result, variations of the non-dynamical profile parameters generically obstruct integrability of a naive Clausius relation expressed solely in terms of mass and entropy. We show that this obstruction is resolved by enlarging the thermodynamic state space to include the profile parameters and by constructing an integrable entropy functional obtained from a radial integral of the geometric radius. The corresponding extended first law contains additional work terms conjugate to the multi-fractional couplings. We analyze both binomial and log-oscillating profiles, clarify the role of presentation dependence, and delineate the consistency conditions required for a well-defined exterior branch with a single horizon. Our results make explicit the separation between profile-insensitive canonical charges and profile-sensitive thermal quantities in multi-fractional black-hole thermodynamics.