arXiv subjects

T. R. Taylor

Publications and source records attributed to T. R. Taylor.

At least 19 recordsLinked to original sources

arXiv2017

SV-map between Type I and Heterotic Sigma Models

The scattering amplitudes of gauge bosons in heterotic and open superstring theories are related by the single-valued projection which yields heterotic amplitudes by selecting a subset of multiple zeta value coefficients in the $α'$ (string tension parameter) expansion of open string amplitudes. In the present work, we argue that this relation holds also at the level of low-energy expansions (or individual Feynman diagrams) of the respective effective actions, by investigating the beta functions of two-dimensional sigma models describing world-sheets of open and heterotic strings. We analyze the sigma model Feynman diagrams generating identical effective action terms in both theories and show that the heterotic coefficients are given by the single-valued projection of the open ones. The single-valued projection appears as a result of summing over all radial orderings of heterotic vertices on the complex plane representing string world-sheet.

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arXiv2010

Deformed Topological Partition Function and Nekrasov Backgrounds

A deformation of the N=2 topological string partition function is analyzed by considering higher dimensional F-terms of the type W^{2g}*Upsilon^n, where W is the chiral Weyl superfield and each Upsilon factor stands for the chiral projection of a real function of N=2 vector multiplets. These terms generate physical amplitudes involving two anti-self-dual Riemann tensors, 2g-2 anti-self-dual graviphoton field strengths and 2n self-dual field strengths from the matter vector multiplets. Their coefficients F_{g,n} generalizing the genus g partition function F_{g,0} of the topological twisted type II theory, can be used to define a generating functional by introducing deformation parameters besides the string coupling. Choosing all matter field strengths to be that of the dual heterotic dilaton supermultiplet, one obtains two parameters that we argue should correspond to the deformation parameters of the Nekrasov partition function in the field theory limit, around the conifold singularity. Its perturbative part can be obtained from the one loop analysis on the heterotic side. This has been computed in [1] and in the field theory limit shown to be given by the radius deformation of c=1 CFT coupled to two-dimensional gravity. Quite remarkably this result reproduces the gauge theory answer up to a phase difference that may be attributed to the regularization procedure. The type II results are expected to be exact and should also capture the part that is non-perturbative in heterotic dilaton.

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arXiv2010

The Hunt for New Physics at the Large Hadron Collider

The Large Hadron Collider presents an unprecedented opportunity to probe the realm of new physics in the TeV region and shed light on some of the core unresolved issues of particle physics. These include the nature of electroweak symmetry breaking, the origin of mass, the possible constituent of cold dark matter, new sources of CP violation needed to explain the baryon excess in the universe, the possible existence of extra gauge groups and extra matter, and importantly the path Nature chooses to resolve the hierarchy problem - is it supersymmetry or extra dimensions. Many models of new physics beyond the standard model contain a hidden sector which can be probed at the LHC. Additionally, the LHC will be a top factory and accurate measurements of the properties of the top and its rare decays will provide a window to new physics. Further, the LHC could shed light on the origin of neutralino masses if the new physics associated with their generation lies in the TeV region. Finally, the LHC is also a laboratory to test the hypothesis of TeV scale strings and D-brane models. An overview of these possibilities is presented in the spirit that it will serve as a companion to the Technical Design Reports (TDRs) by the particle detector groups ATLAS and CMS to facilitate the test of the new theoretical ideas at the LHC. Which of these ideas stands the test of the LHC data will govern the course of particle physics in the subsequent decades.

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arXiv2009

The LHC String Hunter's Companion (II): Five-Particle Amplitudes and Universal Properties

We extend the study of scattering amplitudes presented in ``The LHC String Hunter's Companion'' to the case of five-point processes that may reveal the signals of low mass strings at the LHC and are potentially useful for detailed investigations of fundamental Regge excitations. In particular, we compute the full-fledged string disk amplitudes describing all 2->3 parton scattering subprocesses leading to the production of three hadronic jets. We cast our results in a form suitable for the implementation of stringy partonic cross sections in the LHC data analysis. We discuss the universal, model-independent features of multi-parton processes and point out the existence of even stronger universality relating N-gluon amplitudes to the amplitudes involving N-2 gluons and one quark-antiquark pair. We construct a particularly simple basis of two functions describing all universal five-point amplitudes. We also discuss model-dependent amplitudes involving four fermions and one gauge boson that may be relevant for studying jets associated to Drell-Yan pairs and other processes depending on the spectrum of Kaluza-Klein particles, thus on the geometry of compact dimensions.

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arXiv2006

Amplitude for N-Gluon Superstring Scattering

We consider scattering processes involving N gluonic massless states of open superstrings with certain Regge slope alpha'. At the semi-classical level, the string world-sheet sweeps a disk and N gluons are created or annihilated at the boundary. We present exact expressions for the corresponding amplitudes, valid to all orders in alpha', for the so-called maximally helicity violating configurations, with N=4, 5 and N=6. We also obtain the leading O(alpha'^2) string corrections to the zero-slope N-gluon Yang-Mills amplitudes.

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arXiv2005

Open string topological amplitudes and gaugino masses

We discuss the moduli-dependent couplings of the higher derivative F-terms $(\Tr W^2)^{h-1}$, where $W$ is the gauge N=1 chiral superfield. They are determined by the genus zero topological partition function $F^{(0,h)}$, on a world-sheet with $h$ boundaries. By string duality, these terms are also related to heterotic topological amplitudes studied in the past, with the topological twist applied only in the left-moving supersymmetric sector of the internal $N=(2,0)$ superconformal field theory. The holomorphic anomaly of these couplings relates them to terms of the form $Π^n({\rm Tr}W^2)^{h-2}$, where $Π$'s represent chiral projections of non-holomorphic functions of chiral superfields. An important property of these couplings is that they violate R-symmetry for $h\ge 3$. As a result, once supersymmetry is broken by D-term expectation values, $(\Tr W^2)^2$ generates gaugino masses that can be hierarchically smaller than the scalar masses, behaving as $m_{1/2}\sim m_0^4$ in string units. Similarly, $Π{\rm Tr}W^2$ generates Dirac masses for non-chiral brane fermions, of the same order of magnitude. This mechanism can be used for instance to obtain fermion masses at the TeV scale for scalar masses as high as $m_0\sim{\cal O}(10^{13})$ GeV. We present explicit examples in toroidal string compactifications with intersecting D-branes.

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arXiv2002

Non-Abelian Born-Infeld Action and Type I - Heterotic Duality (II): Nonrenormalization Theorems

Type I - heterotic duality in D=10 predicts various relations and constraints on higher order F^n couplings at different string loop levels on both sides. We prove the vanishing of two-loop corrections to the heterotic F^4 terms, which is one of the basic predictions from this duality. Furthermore, we show that the heterotic F^5 and (CP even) F^6 couplings are not renormalized at one loop. These results strengthen the conjecture that in D=10 any Tr F^(2n) coupling appears only at the disc tree-level on type I side and at (n-1)-loop level on the heterotic side. Our non-renormalization theorems are valid in any heterotic string vacuum with sixteen supercharges.

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arXiv2002

Trilepton Events and B_s -> mu^+ mu^- : No-lose for mSUGRA at the Tevatron?

We study the Tevatron search potential for minimal supergravity (mSUGRA) and find two observables which reveal complementary information on the mSUGRA parameter space: the ``gold-plated'' decays of charginos/neutralinos to trilepton final states and the rare decay B_s-> mu^+ mu^-. For the universal gaugino mass, M_{1/2} below 250 GeV and for the universal scalar fermion mass, M_0 outside of 200-370 GeV we face a ``no-lose'' situation for the Tevatron: If tan(beta) < 30, the Tevatron has a chance to see the trilepton events but not B_s -> mu^+ mu^- during Run IIa, whereas for larger tan(beta) the trilepton events become invisible (at least with an integrated luminosity of 2 fb^{-1}) while B_s -> mu^+ mu^- is enhanced to an observable level. For this study we perform an updated analysis of the trilepton signature which includes the full set of the decay matrix elements and spin correlations. This leads to a new, more promising search reach for the Tevatron.

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arXiv2001

Renormalization of Boundary Fermions and World-Volume Potentials on D-branes

We consider a sigma model formulation of open string theory with boundary fermions carrying Chan-Paton charges at the string ends. This formalism is particularly suitable for studying world-volume potentials on D-branes. We perform explicit two-loop sigma model computations of the potential T-dual to the non-abelian Born-Infeld action. We also discuss the world-volume couplings of NS fluxes which are responsible for Myers' dielectric effect.

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arXiv2000

Branes and Fluxes in D=5 Calabi-Yau Compactifications of M-Theory

We discuss Poincare three-brane solutions in D=5 M-Theory compactifications on Calabi-Yau (CY) threefolds with G-fluxes. We show that the vector moduli freeze at an attractor point. In the case with background flux only, the spacetime geometry contains a zero volume singularity with the three-brane and the CY space shrinking simultaneously to a point. This problem can be avoided by including explicit three-brane sources. We consider two cases in detail: a single brane and, when the transverse dimension is compactified on a circle, a pair of branes with opposite tensions.

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arXiv2000

RR Flux on Calabi-Yau and Partial Supersymmetry Breaking

We show how turning on Flux for RR (and NS-NS) field strengths on non-compact Calabi-Yau 3-folds can serve as a way to partially break supersymmetry from N=2 to N=1 by mass deformation. The freezing of the moduli of Calabi-Yau in the presence of the flux is the familiar phenomenon of freezing of fields in supersymmetric theories upon mass deformations.

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arXiv1999

Thermodynamics of D-brane Probes

We discuss the dynamics and thermodynamics of particle and D-brane probes moving in non-extremal black hole/brane backgrounds. When a probe falls from asymptotic infinity to the horizon, it transforms its potential energy into heat, $TdS$, which is absorbed by the black hole in a way consistent with the first law of thermodynamics. We show that the same remains true in the near-horizon limit, for BPS probes only, with the BPS probe moving from AdS infinity to the horizon. This is a quantitative indication that the brane-probe reaching the horizon corresponds to thermalization in gauge theory. It is shown that this relation provides a way to reliably compute the entropy away from the extremal limit (towards the Schwarzschild limit).

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arXiv1999

Remarks on Two-Loop Free Energy in N=4 Supersymmetric Yang-Mills Theory at Finite Temperature

The strong coupling behavior of finite temperature free energy in N=4 supersymmetric SU(N) Yang-Mills theory has been recently discussed by Gubser, Klebanov and Tseytlin in the context of AdS-SYM correspondence. In this note, we focus on the weak coupling behavior. As a result of a two-loop computation we obtain, in the large N 't Hooft limit, $F(g^2N\to 0)\approx -\frac{π^2}{6}N^2V_3T^4(1-\frac{3}{2π^2}g^2N)$. Comparison with the strong coupling expansion provides further indication that free energy is a smooth monotonic function of the coupling constant.

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arXiv1997

Calculable e^{-1/λ} Effects

We identify and evaluate a class of physical amplitudes in four-dimensional N=4 superstring theory, which receive, in the weak coupling limit, contributions of order e^{-1/λ}, where λis the type II superstring coupling constant. They correspond to four-derivative \Ftilde_1 interaction terms involving the universal type II dilaton supermultiplet. The exact result, obtained by means of a one-loop computation in the dual heterotic theory compactified on T^6, is compared with the perturbation theory on the type II side, and the e^{-1/λ} contributions are associated to non-perturbative effects of Euclidean solitons (D-branes) wrapped on K3 x T^2. The ten-dimensional decompactification limit on the type IIB side validates the recent conjecture for the D-instanton-induced R^4 couplings.

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arXiv1997

Duality in Superstring Compactifications with Magnetic Field Backgrounds

Motivated by the work of Polchinski and Strominger on type IIA theory, where the effect of non-trivial field strengths for p-form potentials on a Calabi-Yau space was discussed, we study four-dimensional heterotic string theory in the presence of magnetic field on a 2-cycle in the internal manifold, for both N=4 and N=2 cases. We show that at special points in the moduli space, certain perturbative charged states become tachyonic and stabilize the vacuum by acquiring vacuum expectation values, thereby restoring supersymmetry. We discuss both the cases where the tachyons appear with a tower of Landau levels, which become light in the limit of large volume of the 2-cycle, and the case where such Landau levels are not present. In the latter case it is sufficient to restrict the analysis to the quartic potential for the tachyon. On the other hand, in the former case it is necessary to include the Landau levels in the analysis of the potential; for toroidal and orbifold examples, we give an explicit CFT description of the new supersymmetric vacuum. The resulting new vacuum turns out to be in the same class as the original supersymmetric one. Finally, using duality, we discuss the role of the Landau levels on the type IIA side.

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arXiv1997

Lectures on Heterotic-Type I Duality

We present a review of heterotic-type I string duality. In particular, we discuss the effective field theory of six- and four-dimensional compactifications with N>1 supersymmetries. We then describe various duality tests by comparing gauge couplings, N=2 prepotentials, as well as higher-derivative F-terms. Based on invited lectures delivered at: 33rd Karpacz Winter School of Theoretical Physics ``Duality, Strings and Fields,'' Przesieka, Poland, 13 - 22 February 1997; Trieste Conference on Duality Symmetries in String Theory, Trieste, Italy, 1 - 4 April 1997; Cargese Summer School ``Strings, Branes and Dualities,'' Cargese, France, 26 May - 14 June 1997.

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arXiv1997

Duality of N=2 Heterotic -- Type I Compactifications in Four Dimensions

We discuss type I -- heterotic duality in four-dimensional models obtained as a Coulomb phase of the six-dimensional U(16) orientifold model compactified on T^2 with arbitrary SU(16) Wilson lines. We show that Kahler potentials, gauge threshold corrections and the infinite tower of higher derivative F-terms agree in the limit that corresponds to weak coupling, large T^2 heterotic compactifications. On the type I side, all these quantities are completely determined by the spectrum of N=2 BPS states that originate from D=6 massless superstring modes.

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arXiv1996

Aspects of Type I - Type II - Heterotic Triality in Four Dimensions

We discuss the equivalence between Type I, Type II and Heterotic N=2 superstring theories in four dimensions. We study the effective field theory of Type I models obtained by orientifold reductions of Type IIB compactifications on $K_3\times T^2$. We show that the perturbative prepotential is determined by the one-loop corrections to the Planck mass and is associated to an index. As is the case for threshold corrections to gauge couplings, this renormalization is entirely due to N=2 BPS states that originate from D=6 massless string modes. We apply our result to the so-called S-T-U model which admits simultaneous Type II and Heterotic descriptions, and show that all three prepotentials agree in the appropriate limits as expected from the superstring triality conjecture.

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