String Theory

In General > s.a. bosonic strings; phenomenology; String Field Theory.
* Idea: The theory of a 2D surface in a d-dimensional flat M, which can be thought of as a field theory on 2D Minkowski, the field being the metric induced on the world-sheet by d-dimensional Minkowski; For a realistic theory one needs to use superstrings, because bosonic strings have tachyons and no fermions.
* Motivation: It automatically includes "gravitons", and, in its susy version, gauge interactions, quark and lepton fields (more naturally than GUTS); It is thought to be finite (almost known to all orders), anomaly-free, and is the only known consistent theory of interacting particles of spin > 2; Has almost no free parameters (only the string tension), and only one fundamenta object.
* Problems: Vacuum non-uniqueness; Dependence of low-energy phenomenology on compactification scheme (no completely satisfactory model given yet); Vanishing of ; Divergent perturbation series (no renormalization needed, but the series is still asymptotic); Lack of underlying general principle; 1994, No known experimental signature.
* Goals: Search for non-metric string theory (in the spirit of topological field theories).
* History: The original phenomenological theory described hadrons as elongated strings, because of the long range forces indicated by the Regge trajectories; With strings considered as fundamental (anomaly cancellations), it became extremely popular in the mid-1980's, and made grandiose claims; Then decrease of interest (J Ehlers: It is in danger of losing contact with thought experiments!), until duality and M-theory came along.
* 4D strings: They are not really (geometrically) strings, but just theories with similar actions in 4D.

Superstrings
* Action: The area of the string in superspace, plus a Wess-Zumino term.
* Consistency: Consistent and well-behaved only in 10D, with gauge group SO(32) or E₈ × E₈ (496 generators).
* Types: There are five consistent types of string theories, Type I (unoriented, open or closed, admit only N = 1 susy); Type II (oriented, closed, with the N = 2 susy required for divergence cancellations–but in type II theories, gauge groups cannot be introduced by attaching quantum numbers to the ends of the strings); Heterotic (oriented closed, N = 1, made chiral by requiring left and right-moving excitations to be different; clockwise modes live in 10D with extra fermionic dimensions, while counterclockwise ones in a 26D bosonic space–the compactification of the extra 16 generates E₈ × E₈); and SO(32) (these groups are associated with the Yang-Mills charges).
* And phenomenology: The particles governed by the two E₈'s can have only gravitational interactions; Maybe we see only one group, the other one accounting for the missing mass.
@ References: Siegel NPB(86) [classical mechanics, Lagrangian and Hamiltonian].

References > s.a. history of physics; quantum spacetime; symplectic structures in general and in physics.
@ Articles: Green & Schwarz PLB(82), NPB(83), PLB(84), PLB(84) [anomaly-free], PLB(85) [likely finite]; Candelas, Horowitz, Strominger & Witten NPB(85); Gross, Harvey, Martinec & Rohm PRL(85), NPB(85), NPB(86) [E₈ × E₈ closed N = 1 heterotic]; Narain PLB(86).
@ I/II: Schwarz PT(87)nov; Davies & Brown 88; Linden PW(90)aug; Kaku 94; Bernstein 96; Duff SA(98)feb; Musser SA(98)oct; Greene pw(00)mar; Susskind pw(03)nov; Greene 03 [interview SA(03)nov]; Chalmers pw(07)sep; Cartwright & Frigg pw(07)sep.
@ Books: Schwarz ed-85; Green, Schwarz & Witten 87; Polyakov 87; Brink & Henneaux 88; Freund & Mahanthappa ed-88; Friedan ed; Casati et al 91; Hatfield 92; Bailin & Love 94; Deligne et al 99 [for mathematicians]; Kaku 99; Szabo 04; Zwiebach 04; Becker et al 07; Dine 07; Kiritsis 07; Becker et al 07.
@ Intros, reviews: Schwarz PRP(82), in(85); Sen lecture notes; Horowitz in(86); Bailin CP(89); issue PTRS(89)#1605; Schwarz ht/96-in, ht/97; Dienes PRP(97); Kiritsis ht/97, ht/97-ln; Schwarz & Seiberg RMP(99)ht/98; Sen ht/98-in; Rudolph ht/98-ln; Álvarez & Meessen JHEP(99); Yoneya ht/00-in; Schwarz ht/00-MG9, hx/00-ln; Sen NPPS(01)ht/00; Mohaupt LNP(03)ht/02; de Boer ht/02-in; Schwarz ap/03-in [update]; Marolf AJP(04)ht/03; Barbón EPJC(04)ht [ideas]; Johnson IJMPA(05); Krishnan ht/06-ln; Zapata ht/06; Schwarz ht/07-in.
@ Quantization: Ohta PRD(86) [BRST]; Carlip & DeWitt-Morette PRL(88) [sign of the metric]; Grassi et al CQG(03) [covariant]; Tseytlin IJMPA(03) [semiclassical]; Guttenberg et al JHEP(04)ht [type II]; Grigore RVMP(07) [bosonic and supersymmetric strings].
@ Conceptual: Witten PTRS(89) [and higher symmetry]; Polyakov PAN(01)ht/00; Woit AS(02)phy/01; Marshakov PU(02)ht [motivation]; Witten ht/02-in [status]; Schnitzer phy/03 [history/philosophy of science]; Kim phy/04 [historical perspective].
@ Critical assessments: Larsson mp/01; Faraggi ht/03-in; Schroer phy/06/IJMPD, ht/06; Hedrich phy/06/P&P, phy/06/SHPMP; Smolin 06; Woit 06; Emam AJP(08)-a0805; Schroer a0805.
@ Nambu-Goto action: Grigore JPA(92); Ramos NPB(98) [reduced covariant phase space quantization]; > s.a. bosonic strings.
@ In curved space: Jain IJMPA(88); Viswanathan & Parthasarathy PRD(97); Sánchez IJMPA(03)ht-in; Orlando & Petropoulos ht/06-ln.
@ Background independence: Rahman ht/97, ht/97.
@ Uniqueness (including p-branes): Bars & Pope GRG(89).
@ And fundamental physics: Gibbs ht/96; Schlesinger FPL(02)ht/00, Brustein & de Alwis PRD(01) [universality].
@ In 4D: Dine ed-88; Meusburger & Rehren CMP(03)mp/02 [algebraic quantization of bosonic string]; Alexandre & Mavromatos ht/07.
@ Networks: Krogh & Lee NPB(98)ht/97; Sen JHEP(98)ht/97; Bhattacharyya et al PRL(98)ht [U-duality]; Verlinde & Vonk ht/03.
@ Substructure: Bergman ht/96, ht/96; Thorn ht/96.
@ Compactification: Reffert a0706-ln [geometric tools].
@ And loop space/spin networks: Ansoldi et al PRD(96), CQG(99); Starodubtsev gq/02; Sathiapalan IJMPA(03)ht/02; Mikovic ht/03; Mikovic ht/05-in [spin foam formulation]; > s.a. bosonic strings.
@ Related topics: Álvarez NPB(83) [with boundaries]; Karliner et al IJMPA(88) [size, shape]; Shapiro & Taylor PRP(90) [spacetime supersymmetric]; 't Hooft NPB(90) [black hole interpretation]; Alvarez-Gaumé HPA(91) [random surfaces]; Witten ht/95; Gibbs ht/95 [and knots]; Hadasz & Rog PLB(96)ht [with particles at the ends]; Abel et al ht/99-in [thermodynamics]; Polchinski & Susskind ht/01 [hadron size]; Schreiber JHEP(04)ht, JHEP(04)ht [(super)-Pohlmeyer invariants].
> Related topics: see anomalies; cosmic strings; instantons; Moduli Space; non-commutative field theory.

Online Resources > s.a. The Official String Theory Website; Wikipedia article.
> Video clips: Discover clip of Brian Greene on String Theory in Two Minutes of Less.

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