Fermionic Superstring Loop Amplitudes in the Pure Spinor Formalism

Σχετικά έγγραφα
6.1. Dirac Equation. Hamiltonian. Dirac Eq.

= {{D α, D α }, D α }. = [D α, 4iσ µ α α D α µ ] = 4iσ µ α α [Dα, D α ] µ.

Space-Time Symmetries

Math221: HW# 1 solutions

Lecture 2: Dirac notation and a review of linear algebra Read Sakurai chapter 1, Baym chatper 3

Higher Derivative Gravity Theories

Phys460.nb Solution for the t-dependent Schrodinger s equation How did we find the solution? (not required)

Revisiting the S-matrix approach to the open superstring low energy eective lagrangian

Srednicki Chapter 55

Reminders: linear functions

MATH423 String Theory Solutions 4. = 0 τ = f(s). (1) dτ ds = dxµ dτ f (s) (2) dτ 2 [f (s)] 2 + dxµ. dτ f (s) (3)

Symmetric Stress-Energy Tensor

Matrices and Determinants

forms This gives Remark 1. How to remember the above formulas: Substituting these into the equation we obtain with

DERIVATION OF MILES EQUATION FOR AN APPLIED FORCE Revision C

Tutorial problem set 6,

CRASH COURSE IN PRECALCULUS

Chapter 6: Systems of Linear Differential. be continuous functions on the interval

Concrete Mathematics Exercises from 30 September 2016

2 Composition. Invertible Mappings

CHAPTER 25 SOLVING EQUATIONS BY ITERATIVE METHODS

Homework 3 Solutions

Jesse Maassen and Mark Lundstrom Purdue University November 25, 2013

derivation of the Laplacian from rectangular to spherical coordinates

Dr. D. Dinev, Department of Structural Mechanics, UACEG

Lecture 13 - Root Space Decomposition II

Spinors and σ-matrices in 10 dimensions It is well known that in D-dimensional space-time Dirac spinor has 2 D 2

HOMEWORK 4 = G. In order to plot the stress versus the stretch we define a normalized stretch:

Απόκριση σε Μοναδιαία Ωστική Δύναμη (Unit Impulse) Απόκριση σε Δυνάμεις Αυθαίρετα Μεταβαλλόμενες με το Χρόνο. Απόστολος Σ.

EE512: Error Control Coding

Partial Differential Equations in Biology The boundary element method. March 26, 2013

Section 7.6 Double and Half Angle Formulas

ECE Spring Prof. David R. Jackson ECE Dept. Notes 2

C.S. 430 Assignment 6, Sample Solutions

Exercises 10. Find a fundamental matrix of the given system of equations. Also find the fundamental matrix Φ(t) satisfying Φ(0) = I. 1.

Lecture 2. Soundness and completeness of propositional logic

Practice Exam 2. Conceptual Questions. 1. State a Basic identity and then verify it. (a) Identity: Solution: One identity is csc(θ) = 1

Orbital angular momentum and the spherical harmonics

Congruence Classes of Invertible Matrices of Order 3 over F 2

Symmetries and Feynman Rules for Ramond Sector in WZW-type Superstring Field Theories

4.6 Autoregressive Moving Average Model ARMA(1,1)

Problem Set 9 Solutions. θ + 1. θ 2 + cotθ ( ) sinθ e iφ is an eigenfunction of the ˆ L 2 operator. / θ 2. φ 2. sin 2 θ φ 2. ( ) = e iφ. = e iφ cosθ.

Chapter 6: Systems of Linear Differential. be continuous functions on the interval

The Simply Typed Lambda Calculus

( ) 2 and compare to M.

UV fixed-point structure of the 3d Thirring model

Section 8.3 Trigonometric Equations

Tridiagonal matrices. Gérard MEURANT. October, 2008

New bounds for spherical two-distance sets and equiangular lines

( y) Partial Differential Equations

3.4 SUM AND DIFFERENCE FORMULAS. NOTE: cos(α+β) cos α + cos β cos(α-β) cos α -cos β

PARTIAL NOTES for 6.1 Trigonometric Identities

If we restrict the domain of y = sin x to [ π, π ], the restrict function. y = sin x, π 2 x π 2

SCHOOL OF MATHEMATICAL SCIENCES G11LMA Linear Mathematics Examination Solutions

Lecture 10 - Representation Theory III: Theory of Weights

If we restrict the domain of y = sin x to [ π 2, π 2

Example Sheet 3 Solutions

Micro-Note on solving super p=2 form A MN

Second Order RLC Filters

Partial Trace and Partial Transpose

DiracDelta. Notations. Primary definition. Specific values. General characteristics. Traditional name. Traditional notation

Problem Set 3: Solutions

Other Test Constructions: Likelihood Ratio & Bayes Tests

arxiv: v2 [hep-th] 4 Jun 2015

Numerical Analysis FMN011

TMA4115 Matematikk 3

DESIGN OF MACHINERY SOLUTION MANUAL h in h 4 0.

Finite Field Problems: Solutions

= λ 1 1 e. = λ 1 =12. has the properties e 1. e 3,V(Y

w o = R 1 p. (1) R = p =. = 1

Geometry of the 2-sphere

Abstract Storage Devices

The ε-pseudospectrum of a Matrix

Homework 8 Model Solution Section

Second Order Partial Differential Equations

1 String with massive end-points

( )( ) ( ) ( )( ) ( )( ) β = Chapter 5 Exercise Problems EX α So 49 β 199 EX EX EX5.4 EX5.5. (a)

Nowhere-zero flows Let be a digraph, Abelian group. A Γ-circulation in is a mapping : such that, where, and : tail in X, head in

SOLVING CUBICS AND QUARTICS BY RADICALS

Hartree-Fock Theory. Solving electronic structure problem on computers

Symmetries and Feynman Rules for Ramond Sector in WZW-type Superstring Field Theories

Derivation of Optical-Bloch Equations

Variational Wavefunction for the Helium Atom

Inverse trigonometric functions & General Solution of Trigonometric Equations

ANSWERSHEET (TOPIC = DIFFERENTIAL CALCULUS) COLLECTION #2. h 0 h h 0 h h 0 ( ) g k = g 0 + g 1 + g g 2009 =?

On the Galois Group of Linear Difference-Differential Equations

9.09. # 1. Area inside the oval limaçon r = cos θ. To graph, start with θ = 0 so r = 6. Compute dr

Phys624 Quantization of Scalar Fields II Homework 3. Homework 3 Solutions. 3.1: U(1) symmetry for complex scalar

Approximation of distance between locations on earth given by latitude and longitude

dim(u) = n 1 and {v j } j i

k A = [k, k]( )[a 1, a 2 ] = [ka 1,ka 2 ] 4For the division of two intervals of confidence in R +

Non-Abelian Gauge Fields

ΚΥΠΡΙΑΚΗ ΕΤΑΙΡΕΙΑ ΠΛΗΡΟΦΟΡΙΚΗΣ CYPRUS COMPUTER SOCIETY ΠΑΓΚΥΠΡΙΟΣ ΜΑΘΗΤΙΚΟΣ ΔΙΑΓΩΝΙΣΜΟΣ ΠΛΗΡΟΦΟΡΙΚΗΣ 19/5/2007

Ordinal Arithmetic: Addition, Multiplication, Exponentiation and Limit

1 11D spinor conventions

6.3 Forecasting ARMA processes

Areas and Lengths in Polar Coordinates

Assalamu `alaikum wr. wb.

PHY 396 K/L. Solutions for problem set #12. Problem 1: Note the correct muon decay amplitude. The complex conjugate of this amplitude

CHAPTER 48 APPLICATIONS OF MATRICES AND DETERMINANTS

Transcript:

Fermionic Superstring Loop Amplitudes in the Pure Spinor Formalism Christian Stahn (UNC) UNC String Theory Seminar, 3 May 2007 based on arxiv:0704.0015

Outline Introduction Methods for kinematic factor evaluation Superfield components Integration in pure spinor superspace Reduction to kinematic bases Application to one- and two-loop amplitudes One loop Two loops Discussion

Pure spinor quantisation of the superstring [Berkovits (2000)] Problems with superstring quantisation: RNS: Spacetime susy only after summation over spin structures GS: Need to go to light cone gauge Flat-space action: S = d 2 z ( 12 x m xm p α θ α pᾱ θᾱ + w α λ wᾱ λᾱ) α + Bosonic ghost λ subject to pure spinor constraint: Critical in ten dimensions. λγ m λ = 0 BRST operator Q = λ α d α : cohomology reproduces superstring spectrum Tree amplitudes agree with RNS [Berkovits & Vallilo (2000)] Relate to GS formalism in semi-lightcone gauge

Pure spinor loop amplitudes Multiloop amplitudes constructed in pure spinor formulation, and used to prove vanishing theorems [Berkovits (2004)]. Massless multiloop amplitude: Need at least four external states. One-loop amplitude: A = K K d 2 τ (Im τ) 5 d 2 z 2 d 2 z 3 d 2 z 4 G(z i, z j ) k i k j Kinematic factors expressed as pure spinor superspace integrals : K 1-loop = (λa)(λγ m W )(λγ n W )F mn i<j K 2-loop = (λγ mnpqr λ)(λγ s W )F mn F pq F rs Covariant zero mode integration: λ 3 θ 5 = 1. Superfields: A α (γ a θ) α ζ a + (uγ a θ)(γ a θ) α +... D β D β and A α Am W α D β F mn, where D α = α + 1 2 k a(γ a θ) α. Bosonic amplitudes agree with RNS [Berkovits & Mafra, Mafra (2005)]

The problems addressed in this talk Evaluation of pure spinor superspace integrals in kinematic factors: K 2-loop = (λγ mnpq[r λ)(λγ s] W (θ))f mn (θ)f pq (θ)f rs (θ) Expand superfields, saturate θ 5 +ka 2 kmk 2 p 3 kr 4 (λγ mnpq[r λ)(λγ s] u 1 )(θγ ab n θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ) + Evaluate correlator = (u 1 γ mpr u 2 )(u 3 γ a u 4 ) + (u 1 γ ai 1i 2 u 2 )(u 3 γ mpr i 1 i 2 u 4 ) + +ε ampr i 1...i 6 (u 1 γ i 3...i 9 u 2 )(u 3 γ i 1i 2 i7i 8 i 9 u 4 ) + Reduce to kinematic basis (Use on-shell identities) K = s 12 [ (u1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) ]

The problems addressed in this talk Evaluation of pure spinor superspace integrals in kinematic factors: K 2-loop = (λγ mnpq[r λ)(λγ s] W (θ))f mn (θ)f pq (θ)f rs (θ) Expand superfields, saturate θ 5 +ka 2 kmk 2 p 3 kr 4 (λγ mnpq[r λ)(λγ s] u 1 )(θγ ab n θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ) + Evaluate correlator = (u 1 γ mpr u 2 )(u 3 γ a u 4 ) + (u 1 γ ai 1i 2 u 2 )(u 3 γ mpr i 1 i 2 u 4 ) + +ε ampr i 1...i 6 (u 1 γ i 3...i 9 u 2 )(u 3 γ i 1i 2 i7i 8 i 9 u 4 ) + Reduce to kinematic basis (Use on-shell identities) K = s 12 [ (u1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) ]

The problems addressed in this talk Evaluation of pure spinor superspace integrals in kinematic factors: K 2-loop = (λγ mnpq[r λ)(λγ s] W (θ))f mn (θ)f pq (θ)f rs (θ) Expand superfields, saturate θ 5 +ka 2 kmk 2 p 3 kr 4 (λγ mnpq[r λ)(λγ s] u 1 )(θγ ab n θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ) + Evaluate correlator = (u 1 γ mpr u 2 )(u 3 γ a u 4 ) + (u 1 γ ai 1i 2 u 2 )(u 3 γ mpr i 1 i 2 u 4 ) + +ε ampr i 1...i 6 (u 1 γ i 3...i 9 u 2 )(u 3 γ i 1i 2 i7i 8 i 9 u 4 ) + Reduce to kinematic basis (Use on-shell identities) K = s 12 [ (u1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) ]

The problems addressed in this talk Evaluation of pure spinor superspace integrals in kinematic factors: K 2-loop = (λγ mnpq[r λ)(λγ s] W (θ))f mn (θ)f pq (θ)f rs (θ) Expand superfields, saturate θ 5 +ka 2 kmk 2 p 3 kr 4 (λγ mnpq[r λ)(λγ s] u 1 )(θγ ab n θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ) + Evaluate correlator = (u 1 γ mpr u 2 )(u 3 γ a u 4 ) + (u 1 γ ai 1i 2 u 2 )(u 3 γ mpr i 1 i 2 u 4 ) + +ε ampr i 1...i 6 (u 1 γ i 3...i 9 u 2 )(u 3 γ i 1i 2 i7i 8 i 9 u 4 ) + Reduce to kinematic basis (Use on-shell identities) K = s 12 [ (u1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) ]

The problems addressed in this talk Evaluation of pure spinor superspace integrals in kinematic factors: K 2-loop = (λγ mnpq[r λ)(λγ s] W (θ))f mn (θ)f pq (θ)f rs (θ) Expand superfields, saturate θ 5 +ka 2 kmk 2 p 3 kr 4 (λγ mnpq[r λ)(λγ s] u 1 )(θγ ab n θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ) + Evaluate correlator = (u 1 γ mpr u 2 )(u 3 γ a u 4 ) + (u 1 γ ai 1i 2 u 2 )(u 3 γ mpr i 1 i 2 u 4 ) + +ε ampr i 1...i 6 (u 1 γ i 3...i 9 u 2 )(u 3 γ i 1i 2 i7i 8 i 9 u 4 ) + Reduce to kinematic basis (Use on-shell identities) K = s 12 [ (u1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) ]

The problems addressed in this talk Evaluation of pure spinor superspace integrals in kinematic factors: K 2-loop = (λγ mnpq[r λ)(λγ s] W (θ))f mn (θ)f pq (θ)f rs (θ) Expand superfields, saturate θ 5 +ka 2 kmk 2 p 3 kr 4 (λγ mnpq[r λ)(λγ s] u 1 )(θγ ab n θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ) + Evaluate correlator = (u 1 γ mpr u 2 )(u 3 γ a u 4 ) + (u 1 γ ai 1i 2 u 2 )(u 3 γ mpr i 1 i 2 u 4 ) + +ε ampr i 1...i 6 (u 1 γ i 3...i 9 u 2 )(u 3 γ i 1i 2 i7i 8 i 9 u 4 ) + Reduce to kinematic basis (Use on-shell identities) K = s 12 [ (u1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) ]

The problems addressed in this talk Evaluation of pure spinor superspace integrals in kinematic factors: K 2-loop = (λγ mnpq[r λ)(λγ s] W (θ))f mn (θ)f pq (θ)f rs (θ) Expand superfields, saturate θ 5 +ka 2 kmk 2 p 3 kr 4 (λγ mnpq[r λ)(λγ s] u 1 )(θγ ab n θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ) + Evaluate correlator = (u 1 γ mpr u 2 )(u 3 γ a u 4 ) + (u 1 γ ai 1i 2 u 2 )(u 3 γ mpr i 1 i 2 u 4 ) + +ε ampr i 1...i 6 (u 1 γ i 3...i 9 u 2 )(u 3 γ i 1i 2 i7i 8 i 9 u 4 ) + Reduce to kinematic basis (Use on-shell identities) K = s 12 [ (u1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) ]

Outline Introduction Methods for kinematic factor evaluation Superfield components Integration in pure spinor superspace Reduction to kinematic bases Application to one- and two-loop amplitudes One loop Two loops Discussion

Superfield recursion relations [Ooguri et al. (2000), Grassi & Tamassia (2004), Policastro & Tsimpis (2006)] A α (x, θ) = 0 + 1 2 (θγa ) α ζ a + 1 3 (θγa ) α (θγ a u) +? A m, W α, F mn =? Choose a gauge θ α A α = 0. On-shell identities 2D (α A β) = γ m αβa m, D α W β = 1 4 (γmn ) α β F mn lead to recursion relations A (n) α = 1 n+1 (γm θ) α A (n 1) m A (n) m = 1 n (θγ mw (n 1) ) W α(n) = 1 2n (γmn θ) α m A (n 1) n where f (n) = 1 n! θαn θ α 1 (Dα1 D αn f ). Can solve: obtain e.g. A (n) m from ζ, u via derivative operator O m q = 1 2 (θγ m qp θ) p : A (2k) m = 1 (2k)! [Ok ] m q ζ q, A (2k+1) m = 1 (2k+1)! [Ok ] m q (θγ q u).

Outline Introduction Methods for kinematic factor evaluation Superfield components Integration in pure spinor superspace Reduction to kinematic bases Application to one- and two-loop amplitudes One loop Two loops Discussion

Pure spinor integrals: Tensorial formulae Recall: Lorentz invariant integration T αβγ,δ 1...δ 5 λ α λ β λ γ θ δ 1... θ δ5 = T (αβγ),[δ 1...δ 5] with normalisation (λγ m θ)(λγ n θ)(λγ p θ)(θγ mnp θ) = 1. Uniquely determined by symmetry λ (α λ β λ γ) : Sym 3 S + = [00003] [10001] θ [δ 1... θ δ5] : Alt 5 S + = [00030] [11010]. Can therefore derive tensorial expressions such as (λγ mnpqr θ)(λγ a θ)(λγ b θ)(θγ cde θ) ( = 1 42 δ mnpqr abcde + ) 1 5! εmnpqr abcde Generally, by Fierzing, reduce to three basic correlators: (λγ [5] λ)(λ{γ [1] or γ [3] or γ [5] }θ)(θγ [3] θ)(θγ [3] θ).

Tensorial formulae: example application Example from two-loop four-fermion amplitudes: F = (λγ mnpq[r λ)(λγ s] u 1 )(θγ n ab θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ). After Fierz transformations: ( F = (λγ mnpq[r λ)(λγ c θ)(θγ ab n θ)(θγ jkl θ) (u 1 γ s] γ c γ b u 2 ) 1 16 + 1 3! 16 + 1 2 5! 16 (λγ mnpq[r λ)(λγ cde θ)(θγ ab n θ)(θγ jkl θ) (u 1 γ s] γ cde γ b u 2 ) (λγ mnpq[r λ)(λγ cdefg θ)(θγ ab n θ)(θγ jkl θ) (u 1 γ s] γ cdefg γ b u 2 )) 1 3! 16 (u 3γ q γ jkl γ s u 4 ), Use correlator formulae such as (λγ mnpqr λ)(λγ abcde θ)(θγ fgh θ)(θγ jkl θ) ( = 16 7 δ mnpqr [ ] δ m n p abc δf j δg d δ q k ( δe h δ r l +2δl e δ r h)+δ m n ab δfg cd δ p q jk (δe h δ r l 3δl e δ r h) Fairly complicated m n p q r + 1 5! εmnpqr m n p q r ) [abcde][fgh][jkl](fgh jkl)

Reduction to traces and bilinears Covariant expression for correlator, using gamma matrices: λ α λ β λ γ θ δ 1... θ δ5 = N 1 [ (γ m ) αδ 1 (γ n ) βδ 2 (γ p ) γδ 3 (γ mnp ) δ 4δ 5 ] (αβγ)[δ 1...δ 5] Normalisation constant N fixed by N (λγ x θ)(λγ y θ)(λγ z θ)(θγ xyz θ) = [ (γ m ) αδ 1 (γ n ) βδ 2 (γ p ) γδ 3 (γ mnp ) δ 4δ 5 ](αβγ)[δ 1...δ 5] (γ x ) αδ1 (γ y ) βδ2 (γ z ) γδ3 (γ xyz ) δ4 δ 5 = 1 60 Tr(γ xγ m ) Tr(γ y γ n ) Tr(γ z γ p ) Tr(γ xyz γ pnm ) +... 1 60 Tr(γ zγ pnm γ zyx γ n γ x γ m γ y γ p ) (60 terms) = 5160960. Use computer algebra to carry out spinor index symmetrisations simplify γ products and traces (e.g. Mathematica with GAMMA)

Reduction to traces and bilinears (2) Allows for easier evaluation of fermionic correlators: N (λγ mnpq[r λ)(λγ s] u 1 )(θγ n ab θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ) = 1 60 Tr(γ xγ ab nγ y γ mnpq[r )(u 3 γ q γ xyz γ s u 4 )(u 1 γ s] γ z γ b u 2 ) +... 1 30 (u 2γ b γ xyz γ q u 3 )(u 1 γ s γ y γ ab nγ x γ mnpq[r γ z γ s] u 4 ), (24 terms) Simpler because: no Fierzing necessary fewer open indices fewer ε terms easier to put on computer

Component approach Can also use gamma matrix expression λ α λ β λ γ θ δ 1... θ δ5 = N 1 [ (γ m ) αδ 1 (γ n ) βδ 2 (γ p ) γδ 3 (γ mnp ) δ 4δ 5 ] to compute correlators of particular spinor components. Example: Check coefficients in t mnm 1n 1...m 4 n 4 (αβγ)[δ 1...δ 5] 10 (λγ p γ m 1n 1 θ)(λγ q γ m 2n 2 θ)(λγ r γ m 3n 3 θ)(θγ m γ n γ pqr γ m 4n 4 θ) ( = 2 45 η mn t m 1n 1...m 4 n 4 ) 8 1 2 εmnm 1n 1...m 4 n 4 Choose particular index values. Expand integrand and evaluate correlators on all monomials (here, about 10 5 ) : (λγ p γ 12 θ)(λγ q γ 21 θ)(λγ r γ 34 θ)(θγ 0 γ 0 γ pqr γ 43 θ) = 12 λ 1 λ 1 λ 1 θ 1 θ 9 θ 10 θ 11 θ 12 + + 12 λ 16 λ 16 λ 16 θ 5 θ 6 θ 7 θ 8 θ 16 = 1 45. Probably unsuitable for more complex applications.

Outline Introduction Methods for kinematic factor evaluation Superfield components Integration in pure spinor superspace Reduction to kinematic bases Application to one- and two-loop amplitudes One loop Two loops Discussion

Purely bosonic expressions Easy to algorithmically deal with bosonic on-shell identitites: momentum conservation i k i = 0 and masslessness ki 2 = 0: eliminate one momentum (e.g. k 4 ) and set all ki 2 to zero eliminate one quadratic invariant (e.g. s 23 s 12 s 13 ) equation of motion for polarisation vector k i ζ i = 0: set all k i ζ i to zero replace one extra k ζ, e.g. k 3 ζ 4 ( k 1 k 2 ) ζ 4 For gauge invariant expressions: start with Fi ab = 2k [a i ζ b] i, e.g. gauge invariant k 4 ζ 1 ζ 2 ζ 3 ζ 4 scalars: Tr(F 1 F 2 F 3 F 4 ) Tr(F 1 F 2 F 4 F 3 ) Tr(F 1 F 3 F 2 F 4 ) Tr(F 1 F 2 ) Tr(F 3 F 4 ) Tr(F 1 F 3 ) Tr(F 2 F 4 ) Tr(F 1 F 4 ) Tr(F 2 F 3 ) gauge invariant k 6 ζ 1 ζ 2 ζ 3 ζ 4 scalars: additionally terms like k 3 F 1 F 2 k 3 Tr(F 3 F 4 ), k 4 F 1 F 3 k 2 Tr(F 2 F 4 )

Fermions: Fierz identities Spinors more complicated. Example question: which scalars from u 1 u 2 u 3 u 4? start from T 1 (1234) = (u 1 γ a u 2 )(u 3 γ a u 4 ), T 3 (1234) = (u 1 γ abc u 2 )(u 3 γ abc u 4 ). Fierz transformations T 3 (1234) = 12T 1 (1234) 24T 1 (1324) (γ a ) (αβ (γ a ) γ)δ = 0 T 1 (1234) + T 1 (1324) + T 1 (1423) = 0 leaves two scalars T 1 (1234) and T 1 (1324) agrees with rep theory, (S + ) 4 = 2 1 +... Easy to computerise in matrix representation for γ a : Reduce to independent monomials u α 1 uβ 2 uγ 3 uδ 4, e.g. T 1 (1234) = 2u 9 1 u9 2 u1 3u 1 4 + 2u 10 1 u10 2 u1 3u 1 4 +...

Fermions: Dirac equation In one- and two-loop amplitudes: need (k 2 or k 4 ) u 1 u 2 u 3 u 4. Spinors subject to /k i u i = 0 Useful observation: only need one k into (u i γ [n] u j ) bilinears. Thus consider (k 2 or k 4 ) (u 1 u 2 u 3 u 4 scalar or 2-tensor) Computer treatment: solve Dirac equation with SO(8) spinors ( ) ( ) ( ) u s u = u c with γ 1...8 u s +u s u c = u c. Obtain coupled equations (k 0 + k 9 )u s (σ k)u c = 0, (k 0 k 9 )u c (σ T k)u s = 0 with solution u s = (σ k)u c / 2k +. Everything reduced to independent monomials in (u c i )1...8

Using particular momenta This algorithm reduces all scalars containing k i and u i to fαβγδ (k i )(u c 1 )α (u c 2 )β (u c 3 )γ (u c 4 )δ Problem: manifest Lorentz invariance broken by γ a matrix rep. difficult to deal with the f αβγδ (k i ) (e.g. terms proportional to ki 2 = 0) One solution: substitute sets of particular vectors for k i, e.g. k µ 1 = (5, 3, 0,..., 0, 4) k µ 2 k µ 3 = (5, 3, 0,..., 4, 0) k µ 4 = ( 5, 0, 3,..., 4, 0) = ( 5, 0, 3,..., 0, 4) Results: Algorithms to find independent scalars, decomposition algorithms, e.g. for k 2 u 1... u 4 scalars, (u 1 /k 3 u 2 )(u 3 /k 1 u 4 ) s 12 T 1 (1234) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) s 13 T 1 (1234) (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) s 13 T 1 (1324)

The problems addressed in this talk Evaluation of pure spinor superspace integrals in kinematic factors: K 2-loop = (λγ mnpq[r λ)(λγ s] W (θ))f mn (θ)f pq (θ)f rs (θ) Expand superfields, saturate θ 5 +ka 2 kmk 2 p 3 kr 4 (λγ mnpq[r λ)(λγ s] u 1 )(θγ ab n θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ) + Evaluate correlator = (u 1 γ mpr u 2 )(u 3 γ a u 4 ) + (u 1 γ ai 1i 2 u 2 )(u 3 γ mpr i 1 i 2 u 4 ) + +ε ampr i 1...i 6 (u 1 γ i 3...i 9 u 2 )(u 3 γ i 1i 2 i7i 8 i 9 u 4 ) + Reduce to kinematic basis (Use on-shell identities) K = s 12 [ (u1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) ]

Outline Introduction Methods for kinematic factor evaluation Superfield components Integration in pure spinor superspace Reduction to kinematic bases Application to one- and two-loop amplitudes One loop Two loops Discussion

One-loop massless four-point amplitude Derived in pure spinor formalism [Berkovits (2004)]: A = K K Kinematic factor: Saturate θ 5 : d 2 τ (Im τ) 5 d 2 z 2 d 2 z 3 d 2 z 4 G(z i, z j ) k i k j K = (λa 1 )(λγ m W 2 )(λγ n W 3 )F 4,mn + ( cycl(234) ) X ABCD = i<j (λa (A) 1 )(λγm W (B) 2 )(λγ n W (C) 3 )F (D) 4,mn with A + B + C + D = 5. Parities of A, B, C, D bosonic or fermionic external states

Four bosons (Review of [Mafra (2005)]) Can evaluate correlator for one labelling, and then symmetrise: K (4B) 1-loop = (λa 1 )(λγ m W 2 )(λγ n W 3 )F 4B 4,mn + ( cycl (234) ) = X 3110 + X 1310 + X 1130 + X 1112 + ( cycl (234) ) Result must be a linear combination of single trace Tr(F (1 F 2 F 3 F 4) ) and double trace Tr(F (1 F 2 ) Tr(F 3 F 4) ). Pure spinor integrals: X 3110 = 15 64 F mnf 1 pqf 2 rsf 3 tu 4 (λγ [t γ pq θ)(λγ u] γ rs θ)(λγ a θ)(θγ amn θ), X 1112 = 15 16 k mζ 4 nf 1 pqf 2 rsf 3 tu 4 (λγ [m γ pq θ)(λγ a] γ rs θ)(λγ n θ)(θγ tu a θ), X 1310 = 5 16 k mζ 3 nf 1 pqf 2 rsf 3 tu 4 (λγ [t γ ma θ)(λγ u] γ rs θ)(λγ n θ)(θγ pq a θ). Reduce to traces: X 3110 = N 1[ 1 60 Tr(γ aγ z ) Tr(γ xyz γ anm ) Tr(γ x γ qp γ [t ) Tr(γ y γ sr γ u] ) + + 1 60 Tr(γ[u γ rs γ zyx γ qp γ t] γ x γ a γ y γ mna γ z ) = ( 1 35 δmp rs δ nq tu 1 630 δmn tu δrs pq 1 90 δmn rs δ pq tu + 26 315 δmn pr δ qs tu ] (60 terms) ) [mn][pq][rs][tu](pq rs)

Four bosons (2) Contract with field strengths, momenta and polarisations, and symmetrise: X 3110 + ( cycl(234) ) = 11 112 Tr(F (1F 2 F 3 F 4) ) 1 56 Tr(F (1F 2 ) Tr(F 3 F 4) ) X 1112 + ( cycl(234) ) = 19 448 Tr(F (1F 2 F 3 F 4) ) 31 1792 Tr(F (1F 2 ) Tr(F 3 F 4) ) X 1310 + ( cycl(234) ) ( = 3 512 4 Tr(F(1 F 2 F 3 F 4) ) Tr(F (1 F 2 ) Tr(F 3 F 4) ) ) Total: K 4B 1-loop = 3 64 ( 4 Tr(F(1 F 2 F 3 F 4) ) Tr(F (1 F 2 ) Tr(F 3 F 4) ) ) = 1 128 t 8F 4 Agrees with Green-Schwarz and RNS results

Four fermions Could similarly evaluate: K (4F) 1-loop = (λa 1 )(λγ m W 2 )(λγ n W 3 )F 4,mn 4F + ( cycl (234) ) Note the symmetry: cycl(234) implies complete antisymmetry in u 2, u 3, u 4 on k 2 u 1 u 2 u 3 u 4 scalars, [234] is equivalent to [1234] there is only one antisymmetric k 2 u 1 u 2 u 3 u 4 scalar Thus the result is fixed by symmetry: K 4F 1-loop (u 1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) Again, agrees with previously known expressions

Symmetrisations more tricky now: Two bosons, two fermions K1-loop(f 2B2F 1 f 2 b 3 b 4 ) = (1 π 34 ) (λa (even) 1 )(λγ m W (even) 2 )(λγ n W (odd) 3 )F (even) 4,mn + (λa (even) 1 )(λγ m W (odd) 3 )(λγ n W (odd) 4 )F (odd) 2,mn. First line has wrong [34] symmetry and must give zero. Fermionic expansion: K 2B2F 1-loop = (1 π 34 ) (X 4010 + X 2210 + X 2030 + X 2012 ) + X 2111, Typical correlator: X 4010 = 1 60 k 1 q k 3 b ζ3 c k 4 mζ 4 n Reduce to u 1 u 2 bilinears: (λγ a θ)(θγ a pq θ)(θγ p u 1 )(λγ [m u 2 )(λγ n] γ bc θ) X 4010 = 1 360 δq[b mn (u 1 γ c] u 2 ) + 1 90 δq[m bc (u 1γ n] u 2 ) + 1 720 δbc mn(u 1 γ q u 2 ) 1 2520 δ[m q (u 1 γ n]bc u 2 ) 1 720 δ[b q (u 1 γ c]mn u 2 ) 1 1260 δ[b [m (u 1γ c]q n] u 2 )+ 1 3360 (u 1γ bcmnq u 2 )

Two bosons, two fermions (2) Contract with k and ζ, and expand in kinematic basis C 1... C 5 : (1 π 34 )X 4010 = 1 60480 ( 1, 12, 12, 1, 2) C 1...C 5 (1 π 34 )X 2210 = 1 60480 (31, 30, 30, 1, 2) C 1...C 5 (1 π 34 )X 2030 = 1 60480 (0, 21, 21, 0, 0) C 1...C 5 (1 π 34 )X 2012 = 1 60480 ( 30, 39, 39, 0, 0) C 1...C 5 X 2111 = 1 480 (1, 0, 4, 1, 0) C 1...C 5 Terms with the wrong [34] symmetry cancel: (1 π 34 ) (X 4010 + X 2210 + X 2030 + X 2012 ) = 0 Remaining part agrees with GS and RNS: ( ) K1-loop 2B2F = X 2111 = 1 480 s 13 (u 2 /ζ 3 (/k 2 +/k 3 )/ζ 4 u 1 )+s 23 (u 2 /ζ 4 (/k 1 +/k 3 )/ζ 3 u 1 )

Outline Introduction Methods for kinematic factor evaluation Superfield components Integration in pure spinor superspace Reduction to kinematic bases Application to one- and two-loop amplitudes One loop Two loops Discussion

Two-loop massless four-point amplitude A = 4 d 2 Ω 11 d 2 Ω 12 d 2 Ω 22 i=1 ( exp ) d 2 i,j k i k j G(z i, z j ) z i (det Im Ω) 5 K (k i, z i ) Fermionic zero mode integrals: K = 12 34 (λγ mnpqr λ)(λγ s ( ) W 1 )F 2,mn F 3,pq F 4,rs + perm(1234) 12 34 K 12 + 13 24 K 13 + 14 23 K 14 Kinematic factors K ij : K 12 = 4 W [1 F 2] F [3 F 4] + 4 W[3 F 4] F [1 F 2] Biholomorphic one-form, ij = (z i, z j ) = ω 1 (z i )ω 2 (z j ) ω 2 (z i )ω 1 (z j )

Four bosons (Review of [Berkovits & Mafra (2005)]) All three kinematic factors equivalent; consider K 4B 12 = 4 W [1 F 2] F [3 F 4] 4B + 4 W [3 F 4] F [1 F 2] 4B = (1 π 12 )(1 π 34 )(1 + π 13 π 24 ) W 1 F 2 F 3 F 4 4B Fermionic expansion: W1 F 2 F 3 F 4B 4 = Y 5000 + Y 1400 + Y 1040 + Y 1004 + + Y 1022 = (1 + π 23 )(1 π 24 ) ( 1 3 Y ) 5000 + Y 1400 + Y 3200 + Y 1022 Introduce symmetrisation operator: K12 4B = ( S 1 4B 3 Y ) 5000 + Y 1400 + Y 3200 + Y 1022, S 4B = (1 π 12 )(1 π 34 )(1 + π 13 π 24 )(1 + π 23 )(1 π 24 ). Non-zero correlators: Y 3200 = 1 192 k a 1 Fcdk 1 mf 2 ef 2 F pqf 3 rs 4 (λγ mnpqr λ)(λγ s γ ab θ)(θγ cd b θ)(θγ ef n θ), Y 1022 = 1 64 F abf 1 mnk 2 p 3 Fcd 3 k r 4 Fef 4 (λγ mnpq[r λ)(λγ s] γ ab θ)(θγ cd q θ)(θγ ef s θ).

Four bosons (2) Symmetriser S 4B projects out k F terms: S 4B (Y 3200 +Y 1022 ) = 1 120 (s 13 s 23 ) ( 4 Tr(F (1 F 2 F 3 F 4) ) Tr(F (1 F 2 ) Tr(F 3 F 4) ) ) Very simple result: K 4B 12 = 1 720 (s 13 s 23 )t 8 F 4 Trivially obtain K 13 and K 14. Total: K2-loop 4B ( ) = 1 720 (s13 s 23 ) 12 34 +(s 12 s 23 ) 13 24 +(s 12 s 13 ) 14 23 t8 F 4 Agrees with (relatively recent!) RNS result [d Hoker, Phong (2001)]. Note product structure, with one half being the one-loop kinematic factor

Very similar calculation: Four fermions K 4F 12 = (1 π 12 )(1 π 34 )(1 + π 13 π 24 ) W 1 F 2 F 3 F 4 4F = 4(1 π 12 ) W 1 F 2 F 3 F 4 4F = S 4F ( 1 3 Y 2111 + Y 0311 ) with symmetrisation S 4F = 4(1 π 12 )(1 π 23 )(1 + π 24 ). Two correlators have to be computed: Y 2111 = ( 2)k 1 a k 2 mk 3 p k 4 r (λγ mnpq[r λ)(λγ s] γ ab θ)(θγ b u 1 )(θγ n u 2 )(θγ q u 3 )(θγ s u 4 ) = 1 5040 ( 19, 21, 21, 19, 17, 17, 0, 0, 0, 0) B 1...B 10, Y 0311 = ( 2 3 )k 2 a k 2 mk 3 p k 4 r (λγ mnpq[r λ)(λγ s] u 1 )(θγ n ab θ)(θγ b u 2 )(θγ q u 3 )(θγ s u 4 ) = 1 15120 ( 14, 16, 0, 2, 8, 8, 0, 5, 5, 0) B 1...B 10.

Four fermions (2) Act with symmetriser S 4F and obtain the one-loop u 4 scalar: K 4F 12 = S 4F ( 1 3 Y 2111 + Y 0311 ) = 1 45 ( 1, 0, 1, 0, 1, 0, 0, 0, 0, 0) B 1...B 10 = 1 45 s 12 ( (u1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) ). Total result, including K 13 and K 14 : K 4F 2-loop = 1 45 (s 12 12 34 s 13 13 24 + s 14 14 23 ) ( (u 1 /k 3 u 2 )(u 3 /k 1 u 4 ) (u 1 /k 2 u 3 )(u 2 /k 1 u 4 ) + (u 1 /k 2 u 4 )(u 2 /k 1 u 3 ) ) Again simple product structure, with one-loop factor

Two bosons, two fermions Exchange symmetry prevents simple product structure with one-loop factor: K2-loop 2B2F 1j kl [ f j (s 12, s 13 )K1-loop(f 2B2F 1 f 2 b 3 b 4 ) ]. j=1,2,3 (Note that any f (s 12, s 13 ) has identical symmetry under 1 2 and 3 4, and is symmetric under (1, 3) (2, 4)). Instead, find with K12 2B2F = (1 π 12 )(1 π 34 ) K K13 2B2F = (2 1 + π 12 + π 34 + 2π 12 π 34 ) K K14 2B2F = (1 + 2π 12 + 2π 34 + π 12 π 34 ) K K = (λ 3 W (even) 1 )F (odd) 2 F (even) 3 F (even) 4 + (λ 3 W (odd) 3 )F (even) 4 F (odd) 1 F (odd) 2

Two bosons, two fermions (2) Correlators in K : combination of ten k 3 u 1 u 2 F 3 F 4 scalars. Images of the symmetrisers are spanned by s 12, s 13 times (u 1 γ a u 2 ) ( ka 3 Fbc 3 F bc 4 2Fab 3 F bck 4 c 1 + 2FabF 4 bc 3 k c 1 ) Tensor structure thus fixed up to three constants: K2-loop 2B2F = [ c 1 s 12 12 34 + (c 2 s 12 + c 3 s 13 ) 13 24 ] +((c 3 c 2 )s 12 + c 3 s 13 ) 14 23 (u 1 γ a u 2 ) ( ka 3 Fbc 3 F bc 4 2Fab 3 F bck 4 c 1 + 2FabF 4 bc 3 k c 1 )

Discussion Summary: The pure spinor formalism yields manifestly supersymmetric loop amplitudes Superspace integration not (much) more complicated for fermions than for bosons Some amplitudes fixed or highly constrained by exchange symmetries Outlook: Improve computer algebra: custom-made Mathematica algorithms vs. specialised program (e.g. Cadabra) Methods applicable to future higher-loop amplitudes