In this work (arXiv:2502.01283) we describe the dynamics of a detector modeled by a harmonic oscillator coupled with an otherwise free quantum field in a curved spacetime in terms of covariant equations of motion leading to local observables. To achieve this, we derive and renormalize the integro-differential equation that governs the detector pointer-variable dynamics, introducing phenomenological parameters such as a dispersion coefficient and a Lamb-shift parameter. Our formal solution, expressed in terms of Green’s functions, allows for the covariant, and causal analysis of induced observables on the field. This formalism can be used for instance to detect non-Gaussianities present in the field’s state.

In this work (arXiv:2504.21833), we introduce a PT-symmetric infinite-dimensional representation of the U_z(sl(2,R)) Hopf algebra, and we analyse a multiparametric family of Hamiltonians constructed from such representation of the generators of this non-standard quantum algebra. It is shown that all these Hamiltonians can be mapped to equivalent systems endowed with a position-dependent mass. From the latter presentation, it is shown how appropriate point canonical transformations can be further defined in order to transform them into Hamiltonians with constant mass over suitable domains. By following this approach, the bound-state spectrum and the corresponding eigenfunctions of the initial PT-symmetric Hamiltonians can be determined. It is worth stressing that a relevant feature of some of the new U_z(sl(2,R)) systems here presented is found to be their connection with double-well and Pöschl-Teller potentials. In fact, as an application we present a particular Hamiltonian that can be expressed as an effective double-well trigonometric potential, which is commonly used to model several relevant systems in molecular physics.

In this work (arXiv:2504.08668), we revisit a problem we addressed in previous publications with various collaborators, that is, the computation of the symmetry resolved entanglement entropies of zero-density excited states in infinite volume. The universal nature of the charged moments of these states has already been noted previously. Here, we investigate this problem further, by writing general formulae for the entropies of excited states consisting of an arbitrary number of subsets of identical excitations. When the initial state is written in terms of qubits with appropriate probabilistic coefficients, we find the final formulae to be of a combinatorial nature too. We analyse some of their features numerically and analytically and find that for qubit states consisting of particles of the same charge, the symmetry resolved entropies are independent of region size relative to system size, even if the number and configuration entropies are not.

Relativistic deformed kinematics leads to a loss of the absolute locality of interactions. In previous studies, some models of noncommutative spacetimes in a two-particle system that implements locality were considered. In this work (arXiv:2504.03378), we present a characterization of the Lie-Poisson algebras formed by the noncommutative space-time coordinates of a multi-particle system and Lorentz generators as a possible restriction on these models. The relativistic deformed kinematics derived from these algebras are also discussed. Finally, we show its connection with cotangent bundle geometries.

Quantum groups have been widely explored as a tool to encode possible nontrivial generalisations of reference frame transformations, relevant in quantum gravity. In quantum information, it was found that the reference frames can be associated to quantum particles, leading to quantum reference frames transformations. The connection between these two frameworks is still unexplored, but if clarified it will lead to a more profound understanding of symmetries in quantum mechanics and quantum gravity. In this paper (arXiv:2504.00569), we establish a correspondence between quantum reference frame transformations and transformations generated by a quantum deformation of the Galilei group with commutative time, taken at the first order in the quantum deformation parameter. This is found once the quantum group noncommutative transformation parameters are represented on the phase space of a quantum particle, and upon setting the quantum deformation parameter to be proportional to the inverse of the mass of the particle serving as the quantum reference frame. These results allow us to show that quantum reference frame transformations are physically relevant when the state of the quantum reference frame is in a quantum superposition of semiclassical states. We conjecture that the all-order quantum Galilei group describes quantum reference frame transformations between more general quantum states of the quantum reference frame.

The symmetric subspace of multi-qubit systems, that is, the space of states invariant under permutations, is commonly encountered in applications in the context of quantum information and communication theory. It is known that the symmetric subspace can be described in terms of irreducible representations of the group SU(2), whose representation spaces form a basis of symmetric states, the so-called Dicke states. In this work (arXiv:2503.23554), we present deformations of the symmetric subspace as deformations of this group structure, which are promoted to a quantum group U_q(𝔰𝔲(2)). We see that deformations of the symmetric subspace obtained in this manner correspond to local deformations of the inner product of each spin, in such a way that departure from symmetry can be encoded in a position-dependent inner product. The consequences and possible extensions of these results are also discussed.

We propose (arXiv:2503.20558) an adaptation of the notion of scaling symmetries for the case of Lie-Hamilton systems, allowing their subsequent reduction to contact Lie systems. As an illustration of the procedure, time-dependent frequency oscillators and time-dependent thermodynamic systems are analyzed from this point of view. The formalism provides a novel method for constructing contact Lie systems on the three-dimensional sphere, derived from recently established Lie-Hamilton systems arising from the fundamental four-dimensional representation of the symplectic Lie algebra 𝔰𝔭(4,ℝ). It is shown that these systems are a particular case of a larger hierarchy of contact Lie systems on a special class of three-dimensional homogeneous spaces, namely the Cayley-Klein spaces. These include Riemannian spaces (sphere, hyperbolic and Euclidean spaces), pseudo-Riemannian spaces (anti-de Sitter, de Sitter and Minkowski spacetimes), as well as Newtonian or non-relativistic spacetimes. Under certain topological conditions, some of these systems retrieve well-known two-dimensional Lie-Hamilton systems through a curvature-dependent reduction.

The spectrum of the quantum Rabi model can be separated as regular eigenvalues that need to be computed numerically and exceptional eigenvalues, that match the energies of a shifted quantum harmonic oscillator. Exceptional values can be separated further as Juddean, if they occur under certain algebraic conditions, and non-Juddean, if they obey more elusive transcendental conditions. In this paper (arXiv:2503.15572), we show that simple assumptions on these conditions imply and extend Braak’s conjecture on the distribution of the quantum Rabi spectrum.

The Kittel-Shore (KS) Hamiltonian describes N spins with long-range interactions that are identically coupled. In this paper (arXiv:2502.20884) , the underlying 𝔰𝔲(2) coalgebra symmetry of the KS model is demonstrated for arbitrary spins, and the quantum deformation of the KS Hamiltonian (q-KS model) is obtained using the corresponding 𝔰𝔲_q(2) quantum group. By construction, the existence of such a symmetry guarantees that all integrability properties of the KS model are preserved under q-deformation. In particular, the q-KS model for spin-1/2 particles is analysed in both ferromagnetic and antiferromagnetic couplings, and the cases with N=2,3, and 4 spins are studied in detail. The higher-spin q-KS models are sketched.

In this paper (arXiv:2502.12750), we study the thermal time hypothesis of arXiv:gr-qc/9406019 in the context of noncommutative deformations of Minkowski. We show that a natural modular group arises from the modular function of the momentum space. In the specific case of κ-Minkowski, we show that this thermal time flow corresponds to the globally defined time coordinate translation. On the other hand, the absence of thermal time for ρ-Minkowski is directly related to the discreteness of its global time. The impact of inner automorphism transformation on the physics and the treatment of unimodular case (unthermalised spacetimes) are discussed. Moreover, a reflection on the use of thermal field theory for quantum gravity phenomenology is put forward, as we just bridged thermal spacetimes with κ-Minkowski, often considered a “flat limit” of a quantum gravity candidate theory.