Cyclicity of All Anti-NMHV and N2^2MHV Tree Amplitudes in N=4 SYM

This article proves the cyclicity of anti-NMHV and N$^2$MHV tree amplitudes in planar N=4 SYM up to any number of external particles as an interesting application of positive Grassmannian geometry. In this proof the two-fold simplex-like structures of tree amplitudes introduced in 1609.08627 play a key role, as the cyclicity of amplitudes will induce similar simplex-like structures for the boundary generators of homological identities. For this purpose, we only need a part of all distinct boundary generators, and the relevant identities only involve BCFW-like cells. The manifest cyclic invariance in this geometric representation reflects one of the invariant characteristics of amplitudes, though they are obtained by the scheme-dependent BCFW recursion relation.Comment: 13 pages, 1 appendi

4-particle Amplituhedron at 3-loop and its Mondrian Diagrammatic Implication

This article provides a direct calculation of the 4-particle amplituhedron at 3-loop order, by introducing a set of practical tricks. After delicately rearranging each piece of this calculation, we find a suggestive connection between positivity conditions and Mondrian diagrams, which will be quantitatively defined. Such a pattern can be generalized for all Mondrian diagrams among all those contribute to the 4-particle integrand of planar N=4 SYM to all loop orders, as a subsequent work 1712.09994 will show.Comment: 32 pages, 3 figures, 1 appendix. Figures improved for v

Note on Identities Inspired by New Soft Theorems

The new soft theorems, for both gravity and gauge amplitudes, have inspired a number of works, including the discovery of new identities related to amplitudes. In this note, we present the proof and discussion for two sets of identities. The first set includes an identity involving the half-soft function which had been used in the soft theorem for one-loop rational gravity amplitudes, and another simpler identity as its byproduct. The second set includes two identities involving the KLT momentum kernel, as the consistency conditions of the KLT relation plus soft theorems for both gravity and gauge amplitudes. We use the CHY formulation to prove the first identity, and transform the second one into a convenient form for future discussion.Comment: 17 page

Derivation of Feynman Rules for Higher Order Poles Using Cross-ratio Identities in CHY Construction

In order to generalize the integration rules to general CHY integrands which include higher order poles, algorithms are proposed in two directions. One is to conjecture new rules, and the other is to use the cross-ratio identity method. In this paper,we use the cross-ratio identity approach to re-derive the conjectured integration rules involving higher order poles for several special cases: the single double pole, single triple pole and duplex-double pole. The equivalence between the present formulas and the previously conjectured ones is discussed for the first two situations.Comment: 29 pages, 11 figure

On Multi-step BCFW Recursion Relations

In this paper, we extensively investigate the new algorithm known as the multi-step BCFW recursion relations. Many interesting mathematical properties are found and understanding these aspects, one can find a systematic way to complete the calculation of amplitude after finite, definite steps and get the correct answer, without recourse to any specific knowledge from field theories, besides mass dimension and helicities. This process consists of the pole concentration and inconsistency elimination. Terms that survive inconsistency elimination cannot be determined by the new algorithm. They include polynomials and their generalizations, which turn out to be useful objects to be explored. Afterwards, we apply it to the Standard Model plus gravity to illustrate its power and limitation. Ensuring its workability, we also tentatively discuss how to improve its efficiency by reducing the steps.Comment: 38 pages, 13 figures, 3 appendice

4-particle Amplituhedronics for 3-5 Loops

Following the direction of 1712.09990 and 1712.09994, this article continues to excavate more interesting aspects of the 4-particle amplituhedron for a better understanding of the 4-particle integrand of planar N=4 SYM to all loop orders, from the perspective of positive geometry. At 3-loop order, we introduce a much more refined dissection of the amplituhedron to understand its essential structure and maximally simplify its direct calculation, by fully utilizing its symmetry as well as the efficient Mondrian way for reorganizing all contributing pieces. Although significantly improved, this approach immediately encounters its technical bottleneck at 4-loop. Still, we manage to alleviate this difficulty by imitating the traditional (generalized) unitarity cuts, which is to use the so-called positive cuts. Given a basis of dual conformally invariant (DCI) loop integrals, we can figure out the coefficient of each DCI topology using its dlog form via positivity conditions. Explicit examples include all 2+5 non-rung-rule topologies at 4- and 5-loop respectively. These results remarkably agree with previous knowledge, which confirms the validity of amplituhedron up to 5-loop and develops a new approach of determining the coefficient of each distinct DCI loop integral.Comment: 45 pages, 20 figures, 2 appendices. Figures improved for v2. More introduction and subsection 1.9 added for v

Holographic Holes in Higher Dimensions

We extend the holographic construction from AdS3 to higher dimensions. In particular, we show that the Bekenstein-Hawking entropy of codimension-two surfaces in the bulk with planar symmetry can be evaluated in terms of the 'differential entropy' in the boundary theory. The differential entropy is a certain quantity constructed from the entanglement entropies associated with a family of regions covering a Cauchy surface in the boundary geometry. We demonstrate that a similar construction based on causal holographic information fails in higher dimensions, as it typically yields divergent results. We also show that our construction extends to holographic backgrounds other than AdS spacetime and can accommodate Lovelock theories of higher curvature gravity.Comment: 46 pages, 17 figures, 1 appendi