Supersymmetric quantum mechanics on the lattice: II. Exact results

Simulations of supersymmetric field theories with spontaneously broken supersymmetry require in addition to the ultraviolet regularisation also an infrared one, due to the emergence of the massless Goldstino. The intricate interplay between ultraviolet and infrared effects towards the continuum and infinite volume limit demands careful investigations to avoid potential problems. In this paper – the second in a series of three – we present such an investigation for N=2 supersymmetric quantum mechanics formulated on the lattice in terms of bosonic and fermionic bonds. In one dimension, the bond formulation allows to solve the system exactly, even at finite lattice spacing, through the construction and analysis of transfer matrices. In the present paper we elaborate on this approach and discuss a range of exact results for observables such as the Witten index, the mass spectra and Ward identities.

Supersymmetric quantum mechanics on the lattice: III. Simulations and algorithms

In the fermion loop formulation the contributions to the partition function naturally separate into topological equivalence classes with a definite sign. This separation forms the basis for an efficient fermion simulation algorithm using a fluctuating open fermion string. It guarantees sufficient tunnelling between the topological sectors, and hence provides a solution to the fermion sign problem affecting systems with broken supersymmetry. Moreover, the algorithm shows no critical slowing down even in the massless limit and can hence handle the massless Goldstino mode emerging in the supersymmetry broken phase. In this paper – the third in a series of three – we present the details of the simulation algorithm and demonstrate its efficiency by means of a few examples.

Compactified N = 1 supersymmetric Yang-Mills theory on the lattice: continuity and the disappearance of the deconfinement transition

Fermion boundary conditions play a relevant role in revealing the confinement mechanism of N=1 supersymmetric Yang-Mills theory with one compactified space-time dimension. A deconfinement phase transition occurs for a sufficiently small compactification radius, equivalent to a high temperature in the thermal theory where antiperiodic fermion boundary conditions are applied. Periodic fermion boundary conditions, on the other hand, are related to the Witten index and confinement is expected to persist independently of the length of the compactified dimension. We study this aspect with lattice Monte Carlo simulations for different values of the fermion mass parameter that breaks supersymmetry softly. We find a deconfined region that shrinks when the fermion mass is lowered. Deconfinement takes place between two confined regions at large and small compactification radii, that would correspond to low and high temperatures in the thermal theory. At the smallest fermion masses we find no indication of a deconfinement transition. These results are a first signal for the predicted continuity in the compactification of supersymmetric Yang-Mills theory.

From doubled Chern–Simons–Maxwell lattice gauge theory to extensions of the toric code

We regularize compact and non-compact Abelian Chern–Simons–Maxwell theories on a spatial lattice using the Hamiltonian formulation. We consider a doubled theory with gauge fields living on a lattice and its dual lattice. The Hilbert space of the theory is a product of local Hilbert spaces, each associated with a link and the corresponding dual link. The two electric field operators associated with the link-pair do not commute. In the non-compact case with gauge group R, each local Hilbert space is analogous to the one of a charged “particle” moving in the link-pair group space R2 in a constant “magnetic” background field. In the compact case, the link-pair group space is a torus U(1)2 threaded by k units of quantized “magnetic” flux, with k being the level of the Chern–Simons theory. The holonomies of the torus U(1)2 give rise to two self-adjoint extension parameters, which form two non-dynamical background lattice gauge fields that explicitly break the manifest gauge symmetry from U(1) to Z(k). The local Hilbert space of a link-pair then decomposes into representations of a magnetic translation group. In the pure Chern–Simons limit of a large “photon” mass, this results in a Z(k)-symmetric variant of Kitaev’s toric code, self-adjointly extended by the two non-dynamical background lattice gauge fields. Electric charges on the original lattice and on the dual lattice obey mutually anyonic statistics with the statistics angle . Non-Abelian U(k) Berry gauge fields that arise from the self-adjoint extension parameters may be interesting in the context of quantum information processing.

Standard model cross-over on the lattice

With the physical Higgs mass the standard model symmetry restoration phase transition is a smooth cross-over. We study the thermodynamics of the cross-over using numerical lattice Monte Carlo simulations of an effective SU(2)×U(1) gauge+Higgs theory, significantly improving on previously published results. We measure the Higgs field expectation value, thermodynamic quantities like pressure, energy density, speed of sound and heat capacity, and screening masses associated with the Higgs and Z fields. While the cross-over is smooth, it is very well defined with a width of only ∼5  GeV. We measure the cross-over temperature from the maximum of the susceptibility of the Higgs condensate, with the result Tc=159.5±1.5  GeV. Outside of the narrow cross-over region the perturbative results agree well with nonperturbative ones.

Nucleon and pion structure with lattice QCD simulations at physical value of the pion mass

We present results on the nucleon scalar, axial, and tensor charges as well as on the momentum fraction, and the helicity and transversity moments. The pion momentum fraction is also presented. The computation of these key observables is carried out using lattice QCD simulations at a physical value of the pion mass. The evaluation is based on gauge configurations generated with two degenerate sea quarks of twisted mass fermions with a clover term. We investigate excited states contributions with the nucleon quantum numbers by analyzing three sink-source time separations. We find that, for the scalar charge, excited states contribute significantly and to a less degree to the nucleon momentum fraction and helicity moment. Our result for the nucleon axial charge agrees with the experimental value. Furthermore, we predict a value of 1.027(62) in the MS¯¯¯¯¯ scheme at 2 GeV for the isovector nucleon tensor charge directly at the physical point. The pion momentum fraction is found to be ⟨x⟩π±u−d=0.214(15)(+12−9) in the MS¯¯¯¯¯ at 2 GeV.

Plug-and-Display: decoration of Virus-Like Particles via isopeptide bonds for modular immunization.

Virus-like particles (VLPs) are non-infectious self-assembling nanoparticles, useful in medicine and nanotechnology. Their repetitive molecularly-defined architecture is attractive for engineering multivalency, notably for vaccination. However, decorating VLPs with target-antigens by genetic fusion or chemical modification is time-consuming and often leads to capsid misassembly or antigen misfolding, hindering generation of protective immunity. Here we establish a platform for irreversibly decorating VLPs simply by mixing with protein antigen. SpyCatcher is a genetically-encoded protein designed to spontaneously form a covalent bond to its peptide-partner SpyTag. We expressed in E. coli VLPs from the bacteriophage AP205 genetically fused to SpyCatcher. We demonstrated quantitative covalent coupling to SpyCatcher-VLPs after mixing with SpyTag-linked to malaria antigens, including CIDR and Pfs25. In addition, we showed coupling to the VLPs for peptides relevant to cancer from epidermal growth factor receptor and telomerase. Injecting SpyCatcher-VLPs decorated with a malarial antigen efficiently induced antibody responses after only a single immunization. This simple, efficient and modular decoration of nanoparticles should accelerate vaccine development, as well as other applications of nanoparticle devices.

Comparison of different lattice definitions of the topological charge

We present a comparison of different definitions of the topological charge on the lattice, using a small-volume ensemble with 2 flavours of dynamical twisted mass fermions. The investigated definitions are: index of the overlap Dirac operator, spectral projectors, spectral flow of the HermitianWilson- Dirac operator and field theoretic with different kinds of smoothing of gauge fields (HYP and APE smearings, gradient flow, cooling). We also show some results on the topological susceptibility.

Modular las voces para llegar a la Historia : Una lectura de 'Bilbao Song', de José Agustín Goytisolo

El artículo se propone a discutir el entrelace entre historia, poesía y ciudad en la obra Taller de arquitectura, de José Agustín Goytisolo, especialmente en su poema 'Bilbao song'. Integrante de la denominada generación de los 50, Goytisolo demostró, frecuentemente, gran preocupación sobre la condición del hombre en la sociedad moderna y su vida en las grandes ciudades. Taller de arquitectura es una obra representativa en el contexto de sus reflexiones sobre el hombre y su entorno. En nuestro texto discutiremos como el poeta articula distintas visiones de la ciudad de Bilbao con los discursos que surgen a lo largo del poema. Para emprender dicha discusión, proponemos un recorrido por la historia política, social y estética del final de los años 60 y principios de los 70 en España, a fin de examinar los procedimientos poéticos utilizados por el autor en la configuración de las relaciones entre historia, poesía y sociedad presentes en 'Bilbao song'. Expondremos como el autor aprehende y modula las voces de 'Bilbao song' utilizándose de la yuxtaposición de imágenes, de historias y de ritmos, para componer un mosaico que revela las diversas caras de la ciudad y de sus gentes bajo el cielo de la dictadura franquista

Modular las voces para llegar a la Historia : Una lectura de 'Bilbao Song', de José Agustín Goytisolo

El artículo se propone a discutir el entrelace entre historia, poesía y ciudad en la obra Taller de arquitectura, de José Agustín Goytisolo, especialmente en su poema 'Bilbao song'. Integrante de la denominada generación de los 50, Goytisolo demostró, frecuentemente, gran preocupación sobre la condición del hombre en la sociedad moderna y su vida en las grandes ciudades. Taller de arquitectura es una obra representativa en el contexto de sus reflexiones sobre el hombre y su entorno. En nuestro texto discutiremos como el poeta articula distintas visiones de la ciudad de Bilbao con los discursos que surgen a lo largo del poema. Para emprender dicha discusión, proponemos un recorrido por la historia política, social y estética del final de los años 60 y principios de los 70 en España, a fin de examinar los procedimientos poéticos utilizados por el autor en la configuración de las relaciones entre historia, poesía y sociedad presentes en 'Bilbao song'. Expondremos como el autor aprehende y modula las voces de 'Bilbao song' utilizándose de la yuxtaposición de imágenes, de historias y de ritmos, para componer un mosaico que revela las diversas caras de la ciudad y de sus gentes bajo el cielo de la dictadura franquista

Modular las voces para llegar a la Historia : Una lectura de 'Bilbao Song', de José Agustín Goytisolo

El artículo se propone a discutir el entrelace entre historia, poesía y ciudad en la obra Taller de arquitectura, de José Agustín Goytisolo, especialmente en su poema 'Bilbao song'. Integrante de la denominada generación de los 50, Goytisolo demostró, frecuentemente, gran preocupación sobre la condición del hombre en la sociedad moderna y su vida en las grandes ciudades. Taller de arquitectura es una obra representativa en el contexto de sus reflexiones sobre el hombre y su entorno. En nuestro texto discutiremos como el poeta articula distintas visiones de la ciudad de Bilbao con los discursos que surgen a lo largo del poema. Para emprender dicha discusión, proponemos un recorrido por la historia política, social y estética del final de los años 60 y principios de los 70 en España, a fin de examinar los procedimientos poéticos utilizados por el autor en la configuración de las relaciones entre historia, poesía y sociedad presentes en 'Bilbao song'. Expondremos como el autor aprehende y modula las voces de 'Bilbao song' utilizándose de la yuxtaposición de imágenes, de historias y de ritmos, para componer un mosaico que revela las diversas caras de la ciudad y de sus gentes bajo el cielo de la dictadura franquista