Letters in Mathematical Physics最新文献

We give explicit formulas for the number of meromorphic differentials on (mathbb{C}mathbb{P}^1) with two zeros and any number of residueless poles and for the number of meromorphic differentials on (mathbb{C}mathbb{P}^1) with one zero, two poles with unconstrained residue and any number of residueless poles, in terms of the orders of their zeros and poles. These are the only two finite families of differentials on (mathbb{C}mathbb{P}^1) with vanishing residue conditions at a subset of poles, up to the action of (textrm{PGL}(2,mathbb {C})). The first family of numbers is related to triple Hurwitz numbers by simple integration and we show its connection with the representation theory of (textrm{SL}_2(mathbb {C})) and the equations of the dispersionless KP hierarchy. The second family has a very simple generating series, and we recover it through surprisingly involved computations using intersection theory of moduli spaces of curves and differentials.

In this note, we show that the potential vector field of a Cotton soliton (M, g, V) is an infinitesimal harmonic transformation, and we use it to give another proof of the triviality of compact Cotton solitons. Moreover, we extend this triviality result to the complete case by imposing certain regularity conditions on the potential vector field V.

CMC (constant mean curvature) Cauchy surfaces play an important role in mathematical relativity as finding solutions to the vacuum Einstein constraint equations is made much simpler by assuming CMC initial data. However, Bartnik (Commun Math Phys 117(4):615–624, 1988) constructed a cosmological spacetime without a CMC Cauchy surface whose spatial topology is the connected sum of two three-dimensional tori. Similarly, Chruściel et al. (Commun Math Phys 257(1):29–42, 2005) constructed a vacuum cosmological spacetime without CMC Cauchy surfaces whose spatial topology is also the connected sum of two tori. In this article, we enlarge the known number of spatial topologies for cosmological spacetimes without CMC Cauchy surfaces by generalizing Bartnik’s construction. Specifically, we show that there are cosmological spacetimes without CMC Cauchy surfaces whose spatial topologies are the connected sum of any compact Euclidean or hyperbolic three-manifold with any another compact Euclidean or hyperbolic three-manifold. Analogous examples in higher spacetime dimensions are also possible. We work with the Tolman–Bondi class of metrics and prove gluing results for variable marginal conditions, which allows for smooth gluing of Schwarzschild to FLRW models.

On vacuum spacetimes of general dimension, we study the linearized Einstein vacuum equations with a spatially compactly supported and (necessarily) divergence-free source. We prove that the vanishing of appropriate charges of the source, defined in terms of Killing vector fields on the spacetime, is necessary and sufficient for solvability within the class of spatially compactly supported metric perturbations. The proof combines classical results by Moncrief with the solvability theory of the linearized constraint equations with control on supports developed by Corvino–Schoen and Chruściel–Delay.

We consider a Dirac operator with constant magnetic field defined on a half-plane with boundary conditions that interpolate between infinite mass and zigzag. By a detailed study of the energy dispersion curves, we show that the infinite mass case generically captures the profile of these curves, which undergoes a continuous pointwise deformation into the topologically different zigzag profile. Moreover, these results are applied to the bulk-edge correspondence. In particular, by means of a counterexample, we show that this correspondence does not always hold true in the zigzag case.

The quantization of chiral fermions on a 3-manifold in an external gauge potential is known to lead to an abelian extension of the gauge group. In this article, we concentrate on the case of (Omega ^3 G) of based smooth maps on a 3-sphere taking values in a compact Lie group G. There is a crossed module constructed from an abelian extension (widehat{Omega ^3 G}) of this group and a group of automorphisms acting on it as explained in a recent article by Mickelsson and Niemimäki. We shall construct a representation of this crossed module in terms of a representation of (widehat{Omega ^3 G}) on a space of functions of gauge potentials with values in a fermionic Fock space and a representation of the automorphism group of (widehat{Omega ^3 G}) as outer automorphisms of the canonical anticommutation relations algebra in the Fock space.

This note is concerned with the linear BBM equation on the half-line. Its nonlinear counterpart originally arose as a model for surface water waves in a channel. This model was later shown to have considerable predictive power in the context of waves generated by a periodically moving wavemaker at one end of a long channel. Theoretical studies followed that dealt with qualitative properties of solutions in the idealized situation of periodic Dirichlet boundary conditions imposed at one end of an infinitely long channel. One notable outcome of these works is the property that solutions become asymptotically periodic as a function of time at any fixed point x in the channel, a property that was suggested by the experimental outcomes. The earlier theory is here generalized using complex-variable methods. The approach is based on the rigorous implementation of the Fokas unified transform method. Exact solutions of the forced linear problem are written in terms of contour integrals and analyzed for more general boundary conditions. For (mathcal C^infty )-data satifisying a single compatibility condition, global solutions obtain. For Dirichlet and Neumann boundary conditions, asymptotic periodicity still holds. However, for Robin boundary conditions, we find not only that solutions lack asymptotic periodicity, but they in fact display instability, growing in amplitude exponentially in time.

We present an algorithm for determining the minimal order differential equations associated with a given Feynman integral in dimensional or analytic regularisation. The algorithm is an extension of the Griffiths–Dwork pole reduction adapted to the case of twisted differential forms. In dimensional regularisation, we demonstrate the applicability of this algorithm by explicitly providing the inhomogeneous differential equations for the multi-loop two-point sunset integrals: up to 20 loops for the equal-mass case, the generic mass case at two- and three-loop orders. Additionally, we derive the differential operators for various infrared-divergent two-loop graphs. In the analytic regularisation case, we apply our algorithm for deriving a system of partial differential equations for regulated Witten diagrams, which arise in the evaluation of cosmological correlators of conformally coupled (phi ^4) theory in four-dimensional de Sitter space.

We discuss dense coding with n copies of a specific preshared state between the sender and the receiver when the encoding operation is limited to the application of group representation. Typically, to act on multiple local copies of these preshared states, the receiver needs quantum memory, because in general the multiple copies will be generated sequentially. Depending on available encoding unitary operations, we investigate what preshared state offers an advantage of using quantum memory on the receiver’s side.