Odd Spatial Dimensions Research Articles

Toward a Ginsparg-Wilson lattice Hamiltonian

To address quantum computation of quantities in quantum chromodynamics (QCD) for which chiral symmetry is important, it would be useful to have the Hamiltonian for a fermion satisfying the Ginsparg-Wilson (GW) equation. I work with a solution to the GW equation which is fractional linear in time derivatives. The resulting Hamiltonian is nonlocal and has ghosts, but is free of doublers and has the correct continuum limit. This construction works in general odd spatial dimensions, and I provide an explicit expression for the Hamiltonian in one spatial dimension. Published by the American Physical Society 2024

Reconstruction of an initial function from the solutions of the fractional wave equation on the light cone trace

We reconstruct the initial functions from the trace of the solution of an initial value problem for the wave equation on the light cone. A method to recover the initial function from the solution of the wave equation on the light cone is already known for odd spatial dimensions. We generalize their work to the fractional wave equation and all dimensions. In other words, we present a method to reconstruct the initial functions from the solution of the fractional wave equation on the light cone.

Dimensional reduction of the Dirac equation in arbitrary spatial dimensions

We investigate the general properties of the dimensional reduction of the Dirac theory, formulated in a Minkowski spacetime with an arbitrary number of spatial dimensions. This is done by applying Hadamard’s method of descent, which consists in conceiving low-dimensional theories as a specialization of high-dimensional ones that are uniform along the additional space coordinate. We show that the Dirac equation reduces to either a single Dirac equation or two decoupled Dirac equations, depending on whether the higher-dimensional manifold has even or odd spatial dimensions, respectively. Furthermore, we construct and discuss an explicit hierarchy of representations in which this procedure becomes manifest and can easily be iterated.

Local Topological Markers in Odd Spatial Dimensions and Their Application to Amorphous Topological Matter.

Local topological markers, topological invariants evaluated by local expectation values, are valuable for characterizing topological phases in materials lacking translation invariance. The Chern marker-the Chern number expressed in terms of the Fourier transformed Chern character-is an easily applicable local marker in even dimensions, but there are no analogous expressions for odd dimensions. We provide general analytic expressions for local markers for free-fermion topological states in odd dimensions protected by local symmetries: a Chiral marker, a local Z marker which in case of translation invariance is equivalent to the chiral winding number, and a Chern-Simons marker, a local Z_{2} marker characterizing all nonchiral phases in odd dimensions. We achieve this by introducing a one-parameter family P_{ϑ} of single-particle density matrices interpolating between a trivial state and the state of interest. By interpreting the parameter ϑ as an additional dimension, we calculate the Chern marker for the family P_{ϑ}. We demonstrate the practical use of these markers by characterizing the topological phases of two amorphous Hamiltonians in three dimensions: a topological superconductor (Z classification) and a topological insulator (Z_{2} classification).

Gauging anomalous unitary operators

Boundary theories of static bulk topological phases of matter are obstructed in the sense that they cannot be realized on their own as isolated systems. The obstruction can be quantified/characterized by quantum anomalies, in particular when there is a global symmetry. Similarly, topological Floquet evolutions can realize obstructed unitary operators at their boundaries. In this paper, we discuss the characterization of such obstructions by using quantum anomalies. As a particular example, we discuss time-reversal symmetric boundary unitary operators in one and two spatial dimensions, where the anomaly emerges as we gauge the so-called Kubo-Martin-Schwinger (KMS) symmetry. We also discuss mixed anomalies between particle number conserving U(1) symmetry and discrete symmetries, such as $C$ and $\mathit{CP}$, for unitary operators in odd spatial dimensions that can be realized at the boundaries of topological Floquet systems in even spatial dimensions.

Disentangling the Generalized Double Semion Model

We analyze the class of Generalized Double Semion (GDS) models in arbitrary dimensions from the point of view of lattice Hamiltonians. We show that on a $d$-dimensional spatial manifold $M$ the dual of the GDS is equivalent, up to constant depth local quantum circuits, to a group cohomology theory tensored with lower dimensional cohomology models that depend on the manifold $M$. We comment on the space-time topological quantum field theory (TQFT) interpretation of this result. We also investigate the GDS in the presence of time reversal symmetry, showing that it forms a non-trivial symmetry enriched toric code phase in odd spatial dimensions.

Elasticity tetrads, mixed axial-gravitational anomalies, and ( 3+1 )-d quantum Hall effect

For two-dimensional topological insulators, the integer and intrinsic (without external magnetic field) quantum Hall effect is described by the gauge anomalous (2+1)-dimensional [2+1d] Chern-Simons (CS) response for the background gauge potential of the electromagnetic U(1) field. The Hall conductance is given by the quantized prefactor of the CS term, which is a momentum-space topological invariant. Here, we show that three-dimensional crystalline topological insulators with no other symmetries are described by a topological (3+1)-dimensional [3+1d] mixed CS term. In addition to the electromagnetic U(1) gauge field, this term contains elasticity tetrad fields $E^{\ a}_{\mu}({\bf r},t) = \partial_{\mu}X^a(\mathbf{r},t)$ which are gradients of crystalline U(1) phase fields $X^a(\mathbf{r},t)$ and describe the deformations of the crystal. For a crystal in three spatial dimensions $a=1,2,3$ and the mixed axial-gravitational response contains three parameters protected by crystalline symmetries: the weak momentum-space topological invariants. The response of the Hall conductance to the deformations of the crystal is quantized in terms of these invariants. In the presence of dislocations, the anomalous 3+1d CS term describes the Callan-Harvey anomaly inflow mechanism. The response can be extended to all odd spatial dimensions. The elasticity tetrads, being the gradients of the lattice U(1) fields, have canonical dimension of inverse length. Similarly, if such tetrad fields enter general relativity, the metric becomes dimensionful, but the physical parameters, such as Newton's constant, the cosmological constant, and masses of particles, become dimensionless.

The point-charge self-energy in a nonminimal Lorentz-violating Maxwell electrodynamics

In this letter we study the self-energy of a point-like charge for the electromagnetic field in a non-minimal Lorentz symmetry breaking scenario in a -dimensional space time. We consider two variations of a model where the Lorentz violation is caused by a background vector that appears in a higher derivative interaction. We restrict our attention to the case where is a time-like background vector, namely , and we verify that the classical self-energy is finite for any odd spatial dimension n and diverges for even n. We also make some comments regarding obstacles in the quantization of the proposed model.

Exact reconstruction formula for the spherical mean Radon transform on ellipsoids

Many modern imaging and remote sensing applications require reconstructing a function from spherical averages (mean values). Examples include photoacoustic tomography, ultrasound imaging or SONAR. Several formulas of the back-projection type for recovering a function in n spatial dimensions from mean values over spheres centered on a sphere have been derived by D Finch, S K Patch and Rakesh (2004 SIAM J. Math. Anal. 35 1213–1240) for odd spatial dimension and by D Finch, M Haltmeier and Rakesh (2007 SIAM J. Appl. Math. 68 392–412) for even spatial dimension. In this paper we generalize some of these formulas to the case where the centers of integration lie on the boundary of an arbitrary ellipsoid. For the special cases n = 2 and n = 3 our results have recently been established by Y Salman (2014 J. Math. Anal. Appl. 420 612–20). For the higher dimensional case we establish proof techniques extending the ones in the above references. Back-projection type inversion formulas for recovering a function from spherical means with centers on an ellipsoid have first been derived by F Natterer (2012 Inverse Problems Imaging 6 315–20) for n = 3 and by V Palamodov (2012 Inverse Problems 28 065014) for arbitrary dimension. The results of Natterer have later been generalized to arbitrary dimension by M Haltmeier (2014 SIAM J. Math. Anal. 46 214–32). Note that these formulas are different from the ones derived in the present paper.

On the multiple hyperbolic systems modelling phase transformation kinetics

We discuss Cahn’s time cone method modelling phase transformation kinetics. The model equation by the time cone method is an integral equation in the space-time region. First, we reduce it to a system of hyperbolic equations, and in the case of odd spatial dimensions, the reduced system is a multiple hyperbolic equation. Next, we propose a numerical method for such a hyperbolic system. By means of alternating direction implicit methods, numerical simulations for practical forward problems are implemented with satisfactory accuracy and efficiency. In particular, in the three dimensional case, our numerical method on the basis of reduced multiple hyperbolic equation is fast.

Electromagnetic and thermal responses of Z topological insulators and superconductors in odd spatial dimensions.

The relation between bulk topological invariants and experimentally observable physical quantities is a fundamental property of topological insulators and superconductors. In the case of chiral symmetric systems in odd spatial dimensions such as time-reversal invariant topological superconductors and topological insulators with sublattice symmetry, this relation has not been well understood. We clarify that the winding number which characterizes the bulk Z nontriviality of these systems can appear in electromagnetic and thermal responses in a certain class of heterostructure systems. It is also found that the Z nontriviality can be detected in the bulk "chiral polarization," which is induced by magnetoelectric effects.

Entanglement entropy of gapped phases and topological order in three dimensions

We discuss entanglement entropy of gapped ground states in different dimensions, obtained on partitioning space into two regions. For trivial phases without topological order, we argue that the entanglement entropy may be obtained by integrating an ``entropy density'' over the partition boundary that admits a gradient expansion in the curvature of the boundary. This constrains the expansion of entanglement entropy as a function of system size and points to an even-odd dependence on dimensionality. For example, in contrast to the familiar result in two dimensions, a size-independent constant contribution to the entanglement entropy can appear for trivial phases in any odd spatial dimension. We then discuss phases with topological entanglement entropy (TEE) that cannot be obtained by adding local contributions. We find that in three dimensions there is just one type of TEE, as in two dimensions, that depends linearly on the number of connected components of the boundary (the ``zeroth Betti number''). In $D>3$ dimensions, new types of TEE appear which depend on the higher Betti numbers of the boundary manifold. We construct generalized toric code models that exhibit these TEEs and discuss ways to extract TEE in $D\ensuremath{\ge}3$.

Valley Spin Sum Rule for Dirac Fermions: Topological Argument

We consider a two-dimensional bipartite lattice system. In such a system, the Bloch band spectrum can have some valley points, around which Dirac fermions appear as the low-energy excitations. Each valley point has a valley spin +1 or -1. In such a system, there are two topological numbers counting vortices and merons in the Brillouin zone, respectively. These numbers are equivalent, and this fact leads to a sum rule which states that the total sum of the valley spins is absent even in a system without time-reversal and parity symmetries. We can see some similarity between the valley spin and chirality in the Nielsen-Ninomiya no-go theorem in odd-spatial dimensions.

Single-particle Green’s functions and interacting topological insulators

We study topological insulators characterized by the integer topological invariant $\mathbb{Z}$, in even and odd spatial dimensions. These are well understood in the case when there are no interactions. We extend the earlier work on this subject to construct their topological invariants in terms of their Green's functions. In this form, they can be used even if there are interactions. Specializing to one and two spatial dimensions, we further show that if two topologically distinct topological insulators border each other, the difference of their topological invariants is equal to the difference between the number of zero-energy boundary excitations and the number of zeros of the Green's function at the boundary. In the absence of interactions Green's functions have no zeros; thus, there are always edge states at the boundary, as is well known. In the presence of interactions, in principle, Green's functions could have zeros. In that case, there could be no edge states at the boundary of two topological insulators with different topological invariants. This may provide an alternative explanation to the recent results on one-dimensional interacting topological insulators.

Comment on ‘Late-time tails of a self-gravitating massless scalar field revisited’

Bizoń et al (2009 Class. Quantum Grav. 26 175006) discuss the power-law tail in the long-time evolution of a spherically symmetric self-gravitating massless scalar field in odd spatial dimensions. They derive explicit expressions for the leading-order asymptotics for solutions with small initial data by using formal series expansions. Unfortunately, this approach misses an interesting observation that the actual decay rate is a product of asymptotic cancellations occurring due to a special structure of the nonlinear terms. Here, we show that one can calculate the leading asymptotics more directly by recognizing the special structure and cancellations already on the level of the wave equation.

POINTWISE ESTIMATES FOR THE WAVE EQUATION WITH DISSIPATION IN ODD SPATIAL DIMENSION

We study the pointwise estimate of solution to the Cauchy problem for the wave equation with viscosity in odd spatial dimension. Through the explicit analysis of the Green function, we obtain the large time behavior of solution, and the solution exhibit the generalized Huygens principle.

Surface Casimir densities and induced cosmological constant in higher dimensional braneworlds

We investigate the vacuum expectation value of the surface energy-momentum tensor for a massive scalar field with general curvature coupling parameter obeying the Robin boundary conditions on two codimension one parallel branes in a $(D+1)$-dimensional background spacetime ${\mathrm{AdS}}_{{D}_{1}+1}\ifmmode\times\else\texttimes\fi{}\ensuremath{\Sigma}$ with a warped internal space $\ensuremath{\Sigma}$. These vacuum densities correspond to a gravitational source of the cosmological constant type for both subspaces of the branes. Using the generalized zeta function technique in combination with contour integral representations, the surface energies on the branes are presented in the form of the sum of single-brane and second-brane-induced parts. For the geometry of a single brane both regions, on the left and on the right of the brane, are considered. At the physical point the corresponding zeta functions contain pole and finite contributions. For an infinitely thin brane taking these regions together, in odd spatial dimensions the pole parts cancel and the total zeta function is finite. The renormalization procedure for the surface energies and the structure of the corresponding counterterms are discussed. The parts in the surface densities generated by the presence of the second brane are finite for all nonzero values of the interbrane separation and are investigated in various asymptotic regions of the parameters. In particular, it is shown that for large distances between the branes the induced surface densities give rise to an exponentially suppressed cosmological constant on the brane. The total energy of the vacuum including the bulk and boundary contributions is evaluated by the zeta function technique and the energy balance between separate parts is discussed.

Surface Casimir densities on a spherical brane in Rindler-like spacetimes

Abstract The vacuum expectation value of the surface energy–momentum tensor is evaluated for a scalar field obeying Robin boundary condition on a spherical brane in ( D + 1 ) -dimensional spacetime Ri × S D − 1 , where Ri is a two-dimensional Rindler spacetime. The generalized zeta function technique is used in combination with the contour integral representation. The surface energies on separate sides of the brane contain pole and finite contributions. Analytic expressions for both these contributions are derived. For an infinitely thin brane in odd spatial dimensions, the pole parts cancel and the total surface energy, evaluated as the sum of the energies on separate sides, is finite. For a minimally coupled scalar field the surface energy–momentum tensor corresponds to the source of the cosmological constant type.

Surface vacuum energy and stresses on a brane in AdS space with an application to the brane-world model

The vacuum expectations of the surface energy-momentum tensor generated on a brane in AdS space-time by quantum fluctuations of a scalar field with an arbitrary coupling parameter are studied. It is assumed that the field satisfies mixed boundary conditions on the brane. A generalized zeta function method is used as a regularization procedure. Two regions, located to the left (L-region) and right (R-region) of the brane, are considered. It is shown that the surface energies for both these regions contain pole and finite contributions. Analytic expressions are derived for both parts. When calculating the total surface energy including the contributions from the L- and R-regions, the pole terms add out in odd spatial dimensions. The surface energy-momentum tensor induced by vacuum quantum effects corresponds to the generation of a cosmological constant on the brane. These results are applied to the second Randall-Sundrum model.

Surface Casimir densities and induced cosmological constant on parallel branes in AdS spacetime

Vacuum expectation value of the surface energy-momentum tensor is evaluated for a massive scalar field with general curvature coupling parameter subject to Robin boundary conditions on two parallel branes located on $(D+1)$-dimensional anti-de Sitter bulk. The general case of different Robin coefficients on separate branes is considered. As a regularization procedure the generalized zeta function technique is used, in combination with contour integral representations. The surface energies on the branes are presented in the form of the sums of single brane and second brane-induced parts. For the geometry of a single brane both regions, on the left (L-region) and on the right (R-region), of the brane are considered. The surface densities for separate L- and R-regions contain pole and finite contributions. For an infinitely thin brane taking these regions together, in odd spatial dimensions the pole parts cancel and the total surface energy is finite. The parts in the surface densities generated by the presence of the second brane are finite for all nonzero values of the interbrane separation. It is shown that for large distances between the branes the induced surface densities give rise to an exponentially suppressed cosmological constant on the brane. In the Randall-Sundrum braneworld model, for the interbrane distances solving the hierarchy problem between the gravitational and electroweak mass scales, the cosmological constant generated on the visible brane is of the right order of magnitude with the value suggested by the cosmological observations.