Fortschritte Der Physik-Progress of Physics最新文献

We define a metric $�G$ on the KBc-subalgebra modulo gauge and describe the worldsheet RG-flow as the gradient flow of the action of cubic open string field theory, where the flow lines are kink-solitons. In particular, for a constant tachyon the gradient flow equations are equivalent to the RG-equations. Additionally, a more general family of gradient flow lines is presented, which describes the RG-flow from the conformal manifold of the D-brane under tachyon condensation. We also derive the stability operator of our solution and show that the zero-modes reflect the invariance of the flow under such marginal perturbations. In fact, the beta function is colinear to our solution such that it describes geodesics from the conformal manifold to the tachyon vacuum with respect to $�G$.

This paper aims to propose a Cardy-like formula characterized by the mass, charge, and angular components of the black hole, along with their corresponding solitonic configuration, obtained through a double Wick rotation. The expression also incorporates the dynamical exponent and effective spatial dimensionality as key elements. To validate the proposal, a new concrete example is presented in which recovery of the semiclassical entropy requires the soliton to possess thermodynamic quantities beyond its mass. Additionally, more examples derived from static black hole solutions are presented, employing a Lorentz boost to calculate their thermodynamic parameters. Finally, a case of a rotating configuration is included, for which the Lorentz boost is not required.

A novel duality sequence is devised to study late-time cosmology in the heterotic $��E_8�\times �E_8�$ setup of Horava and Witten with dynamical walls that are moving towards each other. Remarkably, the dimensionally reduced 4-dimensional theory does not violate NEC and no bouncing or ekpyrotic phase is observed. Instead, the 4-dimensional setup shows a transient de Sitter phase that lies well within the trans-Planckian bound. This opens up a myriad of possibilities of addressing both phenomenological and cosmological issues, with focus on an axionic cosmology with temporally varying axionic coupling.

The finite-curvature phase diagram of improved holographic QCD (IHQCD), a bottom-up holographic model for large $�N_c$ non-supersymmetric $�{\mathrm{YM}}_4$, is investigated. This holographic theory belongs to a class of Einstein-Dilaton theories that exhibit no scaling in the IR. Advanced techniques from dynamical system theory to are employed to address this problem that is harder than other holographic setups. A classification is provided for all solutions in which the dual theory is defined on a constant curvature manifold, both with positive and negative curvature. For general theories in this class, a quantum phase transition occurs at finite curvature. For IHQCD in particular, it is determined that the phase transition occurs at zero curvature.

We follow a new pathway to the definition of the Stochastic Quantization (SQ), first proposed by Parisi and Wu, of the action functional yielding the Einstein equations. Hinging on the functional similarities between the Ricci-Flow equation and the SQ Langevin equations proposed by Rumpf, a novel approach is pushed forward, characterized by a multiplicative noise and a stochastic time that is found to converge to the proper time of a space-like foliation in the equilibrium limit, where quantities are observed to have constant averages. The starting system of equations is expressed using the Arnowitt–Deser–Misner (ADM) variables and their conjugated Hamiltonian momenta. Such a choice is instrumental in understanding the newly derived equations in terms of the breakdown of the diffeomorphism invariance of the classical theory, which instead will hold on average at the steady state. The physical interpretation of the Ricci-flow equations is commented upon, and it is argued that they can naturally provide, in a geometrical way, the renormalization group equation for gravity theories. In the general setting, the equation associated to the shift vector yields the Navier–Stokes equation with a stochastic source. Moreover, it is shown that the fluctuations of the metric tensor components around the equilibrium configurations, far away from the horizon of a Schwarzschild black hole, are forced by the Ricci-flow to follow the Kardar–Parisi–Zhang equation, whose probabilistic distribution can yield an intermittent statistics. Finally, the possible applications of this novel scenario to the cosmological constant are commented upon, and it is argued that the Ricci-flow may provide a solution to the Hubble tension, as a macroscopic effect of scale dependence of the quantum fluctuations of the metric tensor.

The quantum signature of the innermost stable circular orbit (ISCO), a region of profound importance in black hole astrophysics, is investigated. An atom is modeled as an Unruh–DeWitt detector coupled to a massless scalar field in the Boulware vacuum, and the excitation rate is calculated for a detector following a circular geodesic at the ISCO of a Schwarzschild black hole. In stark contrast to the continuous thermal spectra associated with static or infalling observers, the analysis reveals a unique, non-thermal excitation spectrum characterized by a discrete “frequency comb” of sharp, resonant peaks. The locations of these peaks are determined by the orbital frequency at the ISCO, while their intensity increases dramatically as the orbit approaches this final stability boundary. This distinct spectral signature offers a novel theoretical probe of the quantum vacuum in a strong-field gravitational regime and provides a clear distinction between the quantum phenomena experienced by observers on different trajectories. The findings have potential implications for interpreting the emission spectra from accretion disks and open new avenues for exploring the connection between quantum mechanics and gravity.

In the present investigation, the quadratic formulation of $��f�\left(�Q�\right)�$, specifically $��f��\left(�Q�\right)��=�Q�+�\alpha �Q^2�$, is employed incorporating a Gauss–Bonnet term coupled with a scalar field featuring a massless kinetic term and potential. This setup is applied to a spherically symmetric spacetime. An additional degree of freedom is offered by the emergent differential equations offer, which is leveraged to construct a model within this theoretical framework. The feasibility of circumventing ghost instabilities is explored by examining specific constraints tied to the parameters of the assumed black hole. It is shown that our solution always yields a ghost free theory either for large/small $�r$. The solution for the regular black hole involves three constants and is devoid of curvature singularities, which might offer a resolution to the information loss paradox commonly linked to black holes. The inclusion of the Gauss–Bonnet term is interpreted as a correction inspired by string theory, hinting at its possible role in resolving information loss. The thermodynamics and the first law of thermodynamics are shown to hold consistently, provided certain constraints are applied to avoid ghost instabilities.

This study presents an analytical formulation of the greybody factor for a ModMax-AdS black hole surrounded by perfect fluid dark matter, derived by solving the Klein–Gordon equation under appropriate boundary conditions. Through a matching technique between near-horizon and far-field solutions, the absorption probability, energy emission rate as well as the absorption cross-section for massless scalar fields are examined. The influence of physical parameters such as black hole mass, charge, ModMax parameter, cosmological length scale, and dark matter on the effective potential and greybody factor is thoroughly analyzed. The authors' results show that the greybody factor is sensitive to these parameters, with increased black hole mass, charge, and cosmological length scale leading to distinct modulations in the effective potential and greybody factor, indicating enhanced or reduced wave interactions. Additionally, the study incorporates the implications of the generalized uncertainty principle and dark matter on bosonic tunneling, revealing modified temperature and stability properties of the black hole. These findings manifest significant insights into the quantum field dynamics around black holes in curved spacetimes and contribute to the understanding of black hole thermodynamics in the presence of nonlinear electrodynamics and exotic matter.

A bundle geometric formulation of non-relativistic many-particles Quantum Mechanics is presented. A wave function is seen to be a $�C$-valued cocyclic tensorial 0-form on configuration space-time seen as a principal bundle, while the Schrödinger equation flows from its covariant derivative, with the action functional supplying a (flat) cocyclic connection 1-form on the configuration bundle. In line with the historical motivations of Dirac and Feynman, ours is thus a Lagrangian geometric formulation of QM, in which the Dirac–Feynman path integral arises in a geometrically natural way.

Applying the dressing field method, we obtain a relational reformulation of this geometric non-relativistic QM: a relational wave function is realised as a basic cocyclic 0-form on the configuration bundle. In this relational QM, any particle position can be used as a dressing field, i.e., as a “physical reference frame.” The dressing field method naturally accounts for the freedom in choosing the dressing field, which is readily understood as a covariance of the relational formulation under changes of physical reference frame.