functorial quantum field theory
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FQFT and cohomology
superalgebra and (synthetic ) supergeometry
In perturbative string theory scattering amplitudes are defined as in quantum field theory, but with n-point functions of 1-dimensional worldline theories (Feynman diagrams) replaced by those of worldsheet 2d CFTs.
graphics grabbed from Jurke 10
The amplitudes are thought (see the commented references below) to come out term-wise (for each “loop order” hence for each genus and number of punctures of (super-)Riemann surfaces) finite (at least UV-finite), hence renormalized: the higher string oscillations may be seen as providing canonical counterterms for the massless excitations in the effective field theory. In this sense string theory provides a UV-completion of these effective field theories (supergravity coupled to Yang-Mills theory).
The full perturbation series is the sum of all these (finite) contributions over the genera of Riemann surfaces (the “loop orders”). This sum diverges, even if all loop orders are finite. Notice though, that a non-trivial perturbative QFT is not supposed to have a finite radius of convergence of its scattering amplitudes, since that would imply convergence also for negative coupling constant, which is physically unreasonable. (For the bosonic string the perturbation series has apparently been explicitly shown not to be Borel resummable.) For more on this see at non-perturbative effect and string theory FAQ – Is the divergence of the pertubation series fatal?.
A string scattering amplitude is called UV-finite at a given loop order (genus of a Riemann surface $\Sigma$ with $n$ marked points/string insertions) if the correlation function $\langle \phi_1, \cdots, \phi_n\rangle_{\Sigma}$ is finite for every single such Riemann surface. The actual string amplitude at order $(g,n)$ though is the averaging of this over all possible conformal structures on $\Sigma$, hence the integration of the correlation function, as a function on the conformal structure, over the compactified moduli space of conformal structures $\mathcal{M}_{g,n}$ (a Deligne-Mumford stack).
If also this integral is finite, hence if the total measure on the moduli space of conformal structures is finite, then one says the amplitude is IR-finite.
This distinction between UV-finiteness and IR-finiteness is not always highlighted in all of the articles below. All authors argue that the string is UV-finite to all order. The IR-finiteness is only discussed much more recently at low loop order.
IR non-finiteness is not physically fatal. For instance if a perturbative theory of quantum gravity develops a cosmological constant perturbatively, then the perturbation series will be IR-divergent, signifying the fact that background spacetime without cosmological constant is no longer a solution to the quantum-corrected equations of motion. Nevertheless, these potential IR-divergences seem to be absent for the superstring perturbation series. For the cosmological constant case this can already be seen from the fact that the effective QFT of type II supergravity etc. does not admit a cosmological constant, for that would violate supersymmetry.
The open/closed string duality implies certain relations in string scattering amplitudes that in the point-particle limit induces relations between scattering amplitudes in Yang-Mills theory and in gravity. These are the KLT relations in QFT. See in particular Mafra-Schlotterer 18a, Mafra-Schlotterer 18b, Mafra-Schlotterer 18c.
The scattering amplitudes in twistor string theory induce the MHV amplitudes in (super-)Yang-Mills theory. See at string theory results applied elsewhere in the section Application to QCD – Scattering amplitudes.
The Veneziano amplitude (open bosonic string tree-level scattering) has an equivalent formulation as the inverse product over all prime numbers $p$ of an amplitude computed not by an integral in the real but in the p-adic numbers. For other open string amplitudes this holds up to some regularization. This is the topic of p-adic string theory, see there for more details.
A comprehensive account of the superstring S-matrix may be obtained from combining the general idea presented in
with the technical details laid out in
Edward Witten, Superstring Perturbation Theory Revisited (arXiv:1209.5461)
Edward Witten, More On Superstring Perturbation Theory: An Overview Of Superstring Perturbation Theory Via Super Riemann Surfaces (arXiv:1304.2832)
Survey of the tree level string scattering amplitudes includes
Ralph Blumenhagen, Dieter Lüst, Stefan Theisen, String Scattering Amplitudes and Low Energy Effective Field Theory, chapter 16 in Basic Concepts of String Theory Part of the series Theoretical and Mathematical Physics pp 585-639 Springer 2013 (TOC pdf, publisher page)
Katrin Becker, Melanie Becker, Ilarion V. Melnikov, Daniel Robbins, Andrew B. Royston, Some tree-level string amplitudes in the NSR formalism, JHEP 12 (2015) 010 (arXiv:1507.02172)
See also
Gregory Moore, Symmetries of the Bosonic String S-Matrix (arXiv:hep-th/9310026)
Gaston Giribet, Nicholas Labranche, Joan La Madrid, Comments on the two-point string amplitudes [arXiv:2303.15658]
On string scattering amplitudes in view of the S-matrix bootstrap:
For more references see also at string theory results applied elsewhere.
A review of superstring scattering amplitudes is in the last section of (Staessens-Vernocke 10). A general discussion of the problem of superstring amplitudes is in
Eric D'HokerDuong Phong, Loop amplitudes for the fermionic string, Nucl. Phys. B 278 (1986) 225;
Greg Moore, P. Nelson, Joseph Polchinski, Strings and supermoduli, Phys. Lett. B 169 (1986) 47-53.
On analycity of the superstring S-matrix:
Survey of the presence and role of divergences includes
Discussion of superstring scattering amplitudes in terms of pure spinors (Berkovits superstring) with emphasis on KLT relations:
Carlos Mafra, Oliver Schlotterer, Towards the $n$-point one-loop superstring amplitude I: Pure spinors and superfield kinematics (arXiv:1812.10969)
Carlos Mafra, Oliver Schlotterer, Towards the $n$-point one-loop superstring amplitude II: Worldsheet functions and their duality to kinematics (arXiv:1812.10970)
Carlos Mafra, Oliver Schlotterer, Towards the $n$-point one-loop superstring amplitude III: One-loop correlators and their double-copy structure (arXiv:1812.10971)
Carlos R. Mafra, Oliver Schlotterer, Tree-level amplitudes from the pure spinor superstring [arXiv:2210.14241]
For more see also at superstring field theory, such as
The 1-loop amplitudes in type II string theory have been discussed in
and for heterotic string theory in
The description of 2-loop amplitudes, including the integration over the super-moduli space of conformal structures in superstring theory:
Eric D'Hoker, Duong Phong, Two-Loop Superstrings I, Main Formulas, Phys. Lett. B529:241-255, 2002 (arXiv:hep-th/0110247)
Eric D'Hoker, Duong Phong, Two-Loop Superstrings II, The Chiral Measure on Moduli Space, Nucl. Phys. B636:3-60, 2002 (arXiv:hep-th/0110283)
Eric D'Hoker, Duong Phong, Two-Loop Superstrings III, Slice Independence and Absence of Ambiguities, Nucl. Phys. B636:61-79, 2002 (arXiv:hep-th/0111016)
Eric D'Hoker, Duong Phong, Two-Loop Superstrings IV, The Cosmological Constant and Modular Forms, Nucl. Phys. B639:129-181, 2002 (arXiv:hep-th/0111040)
Eric D'Hoker, Duong Phong, Two-Loop Superstrings V: Gauge Slice Independence of the N-Point Function, Nucl. Phys. B715:91-119, 2005 (arXiv:hep-th/0501196)
Eric D'Hoker, Duong Phong, Two-Loop Superstrings VI: Non-Renormalization Theorems and the 4-Point Function, Nucl. Phys. B715:3-90, 2005 (arXiv:hep-th/0501197)
Eric D'Hoker, Duong Phong, Two-Loop Superstrings VII, Cohomology of Chiral Amplitudes, Nucl. Phys. B804:421-506, 2008 (arXiv:0711.4314)
Review of this work:
Further development in:
Eric D'Hoker, Carlos Mafra, Boris Pioline, Oliver Schlotterer, Two-loop superstring five-point amplitudes I: Construction via chiral splitting and pure spinors (arXiv:2006.05270)
Eric D'Hoker, Carlos Mafra, Boris Pioline, Oliver Schlotterer, Two-loop superstring five-point amplitudes II: Low energy expansion and S-duality (doi:2008.08687)
The technical issue of the moduli space of super Riemann surfaces of higher genus (for higher loop string scattering amplitudes) is discussed in
Edward Witten, Notes On Super Riemann Surfaces And Their Moduli (arXiv:1209.2459)
Ron Donagi, Edward Witten, Supermoduli Space Is Not Projected (arXiv:1304.7798)
Here is a commented list of references on the degreewise finiteness of string scattering amplitudes.
Introductory lecture notes include
Discussion of the term-wise finiteness of the bosonic string scattering amplitudes is in
There are also arguments in
Finiteness of heterotic and type II superstring $n$-point functions in flat spacetime is argued for in
General finiteness of superstring amplitudes is discussed in
which shows that a certain divergence which could appear does not.
Also
argues finiteness of the superstring amplitudes at each order.
Also
Eric D'Hoker, Duong Phong, Momentum Analyticity and Finiteness of the 1-Loop Superstring Amplitude, Phys. Rev. Lett. 70 (1993) 3692-3695 (arXiv:hep-th/9302003)
Eric D'Hoker, Duong Phong, The Box Graph In Superstring Theory, Nucl.Phys.B440:24-94,1995 (arXiv:hep-th/9410152)
Eric D'Hoker, Duong Phong, Dispersion Relations in String Theory; Nucl.Phys.B440:24-94,1995 (arXiv:hep-th/9404128)
Arguments for the finiteness of superstring scattering amplitudes to all loop order based on the Berkovits superstring-formulation have been promoted in
(In footnote 2 this article claims that the claimed proofs of the same statement by G.S Danilov in hep-th/9801013, hep-th/0312177 are not in fact proofs.)
Discussion of 2-loop amplitudes from holomorphy arguments is in
See also
Computation of graviton scattering amplitudes (perturbative quantum gravity):
Taejin Lee, Gravitational Scattering Amplitudes and Closed String Field Theory in the Proper-Time Gauge, EPJ Web of Conferences 168, 07004 (2018) (doi:10.1051/epjconf/201816807004)
Taejin Lee, Four-Graviton Scattering and String Path Integral in the Proper-time gauge (arXiv:1806.02702)
Discussion via AdS/CFT beyond the SCFT planar limit, using the conformal bootstrap:
On point-particle limit via tropical geometry
Scattering amplitudes of highly excited strings:
Last revised on March 29, 2023 at 07:22:00. See the history of this page for a list of all contributions to it.