245 research outputs found
Efficient Learning of a One-dimensional Density Functional Theory
Density functional theory underlies the most successful and widely used
numerical methods for electronic structure prediction of solids. However, it
has the fundamental shortcoming that the universal density functional is
unknown. In addition, the computational result---energy and charge density
distribution of the ground state---is useful for electronic properties of
solids mostly when reduced to a band structure interpretation based on the
Kohn-Sham approach. Here, we demonstrate how machine learning algorithms can
help to free density functional theory from these limitations. We study a
theory of spinless fermions on a one-dimensional lattice. The density
functional is implicitly represented by a neural network, which predicts,
besides the ground-state energy and density distribution, density-density
correlation functions. At no point do we require a band structure
interpretation. The training data, obtained via exact diagonalization, feeds
into a learning scheme inspired by active learning, which minimizes the
computational costs for data generation. We show that the network results are
of high quantitative accuracy and, despite learning on random potentials,
capture both symmetry-breaking and topological phase transitions correctly.Comment: 5 pages, 3 figures; 4+ pages appendi
News from FormCalc and LoopTools
The FormCalc package automates the computation of FeynArts amplitudes up to
one loop including the generation of a Fortran code for the numerical
evaluation of the squared matrix element. Major new or enhanced features in
Version 5 are: iterative build-up of essentially arbitrary phase-spaces
including cuts, convolution with density functions, and uniform treatment of
kinematical variables. The LoopTools library supplies the one-loop integrals
necessary for evaluating the squared matrix element. Its most significant
extensions in Version 2.2 are the five-point family of integrals, and complex
and alternate versions.Comment: 5 pages, to appear in the proceedings of the 7th International
Symposium on Radiative Corrections (RADCOR05), Shonan Village, Japan, 200
Optimisation of expression and purification of the feline and primate foamy virus transmembrane envelope proteins using a 96 deep well screen
The production of recombinant transmembrane proteins is due to their biochemical properties often troublesome and time consuming. Here the prokaryotic expression and purification of the transmembrane envelope proteins of the feline and primate foamy viruses using a screening assay for optimisation of expression in 96 deep well plates is described. Testing simultaneously various bacterial strains, media, temperatures, inducer concentrations and different transformants, conditions for an about twentyfold increased production were quickly determined. These small scale test conditions could be easily scaled up, allowing purification of milligram amounts of recombinant protein. Proteins with a purity of about 95% were produced using a new purification protocol, they were characterised by gel filtration and circular dichroism and successfully applied in immunological assays screening for foamy virus infection and in immunisation studies. Compared to the previously described protocol (M. Mühle, A. Bleiholder, S. Kolb, J. Hübner, M. Löchelt, J. Denner, Immunological properties of the transmembrane envelope protein of the feline foamy virus and its use for serological screening, Virology 412 (2011) 333–340), proteins with similar characteristics but about thirtyfold increased yields were obtained. The screening and production method presented here can also be applied for the production of transmembrane envelope proteins of other retroviruses, including HIV-1
Infernal and Exceptional Edge Modes: Non-Hermitian Topology Beyond the Skin Effect
The classification of point gap topology in all local non-Hermitian symmetry
classes has been recently established. However, many entries in the resulting
periodic table have only been discussed in a formal setting and still lack a
physical interpretation in terms of their bulk-boundary correspondence. Here,
we derive the edge signatures of all two-dimensional phases with intrinsic
point gap topology. While in one dimension point gap topology invariably leads
to the non-Hermitian skin effect, non-Hermitian boundary physics is
significantly richer in two dimensions. We find two broad classes of
non-Hermitian edge states: (1) Infernal points, where a skin effect occurs only
at a single edge momentum, while all other edge momenta are devoid of edge
states. Under semi-infinite boundary conditions, the point gap thereby closes
completely, but only at a single edge momentum. (2) Non-Hermitian exceptional
point dispersions, where edge states persist at all edge momenta and furnish an
anomalous number of symmetry-protected exceptional points. Surprisingly, the
latter class of systems allows for a finite, non-extensive number of edge
states with a well defined dispersion along all generic edge terminations.
Instead, the point gap only closes along the real and imaginary eigenvalue
axes, realizing a novel form of non-Hermitian spectral flow.Comment: 6 pages, 3 figures, 13 pages supplementary materia
Infernal and exceptional edge modes: non-Hermitian topology beyond the skin effect
The classification of point gap topology in all local non-Hermitian (NH) symmetry classes has been recently established. However, many entries in the resulting periodic table have only been discussed in a formal setting and still lack a physical interpretation in terms of their bulk-boundary correspondence. Here, we derive the edge signatures of all two-dimensional phases with intrinsic point gap topology. While in one dimension point gap topology invariably leads to the NH skin effect, NH boundary physics is significantly richer in two dimensions. We find two broad classes of non-Hermitian edge states: (1) infernal points, where a skin effect occurs only at a single edge momentum, while all other edge momenta are devoid of edge states. Under semi-infinite boundary conditions, the point gap thereby closes completely, but only at a single edge momentum. (2) NH exceptional point dispersions, where edge states persist at all edge momenta and furnish an anomalous number of symmetry-protected exceptional points. Surprisingly, the latter class of systems allows for a finite, non-extensive number of edge states with a well defined dispersion along all generic edge terminations. Concomitantly, the point gap only closes along the real and imaginary eigenvalue axes, realizing a novel form of NH spectral flow
Neutrino Mass Matrix Running for Non-Degenerate See-Saw Scales
We consider the running of the neutrino mass matrix in the Standard Model and
the Minimal Supersymmetric Standard Model, extended by heavy singlet Majorana
neutrinos. Unlike previous studies, we do not assume that all of the heavy mass
eigenvalues are degenerate. This leads to various effective theories when the
heavy degrees of freedom are integrated out successively. We calculate the
Renormalization Group Equations that govern the evolution of the neutrino mass
matrix in these effective theories. We show that an appropriate treatment of
the singlet mass scales can yield a substantially different result compared to
integrating out the singlets at a common intermediate scale.Comment: 12 pages, 9 figure
The Quartic Higgs Coupling at Hadron Colliders
The quartic Higgs self-coupling is the final measurement in the Higgs
potential needed to fully understand electroweak symmetry breaking. None of the
present or future colliders are known to be able to determine this parameter.
We study the chances of measuring the quartic self-coupling at hadron colliders
in general and at the VLHC in particular. We find the prospects challenging.Comment: 5 pages, 4 figure
Symmetry breaking and spectral structure of the interacting Hatano-Nelson model
We study the Hatano-Nelson model, i.e., a one-dimensional non-Hermitian chain of spinless fermions with nearest-neighbor nonreciprocal hopping, in the presence of repulsive nearest-neighbor interactions. At half filling, we find two PT transitions, as the interaction strength increases. The first transition is marked by an exceptional point between the first and the second excited state in a finite-size system and is a first-order symmetry-breaking transition into a charge-density wave regime. Persistent currents characteristic of the Hatano-Nelson model abruptly vanish at the transition. The second transition happens at a critical interaction strength that scales with the system size and can thus only be observed in finite-size systems. It is characterized by a collapse of all energy eigenvalues onto the real axis. We further show that in a strong interaction regime, but away from half filling, the many-body spectrum shows point gaps with nontrivial winding numbers, akin to the topological properties of the single-particle spectrum of the Hatano-Nelson chain, which indicates the skin effect of extensive many-body eigenstates under open boundary conditions. Our results can be applied to other models such as the non-Hermitian Su-Schrieffer-Heeger-type model and contribute to an understanding of fermionic many-body systems with non-Hermitian Hamiltonians
Symmetry Indicators for Inversion-Symmetric Non-Hermitian Topological Band Structures
We characterize non-Hermitian band structures by symmetry indicator
topological invariants. Enabled by crystalline inversion symmetry, these
indicators allow us to short-cut the calculation of conventional non-Hermitian
topological invariants. In particular, we express the three-dimensional winding
number of point-gapped non-Hermitian systems, which is defined as an integral
over the whole Brillouin zone, in terms of symmetry eigenvalues at
high-symmetry momenta. Furthermore, for time-reversal symmetric non-Hermitian
topological insulators, we find that symmetry indicators characterize the
associated Chern-Simons form, whose evaluation usually requires a
computationally expensive choice of smooth gauge. In each case, we discuss the
non-Hermitian surface states associated with nontrivial symmetry indicators.Comment: 6 pages, 1 figure, supplement include
Precise predictions for W \gamma \gamma +jet production at hadron colliders
In this letter we report on a calculation of W gamma gamma + jet production
at next-to-leading order QCD. We include the leptonic decays of the W and take
into account all off-shell and finite width effects. This is the first
computation which falls into the category of triboson+jet production at
next-to-leading order QCD. In total we find sizable corrections with nontrivial
phase space dependencies. Therefore, our results are important for
phenomenological analyses such as the extraction of anomalous electroweak
quartic couplings from inclusive hadron collider data.Comment: 6 pages, 6 figure
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