String Physics Research Articles

Emergent potentials and non-perturbative open topological strings

We show that integrating out M2 branes ending on M5 branes inside Calabi-Yau manifolds captures non-perturbative open topological string physics. The integrating out is performed using a contour integral in complexified Schwinger proper time. For the resolved conifold, this contour can be extended to include the zero pole, which we argue captures the ultraviolet completion of the integrating out and yields the tree-level polynomial terms in the free energy. This is a manifestation of the Emergence Proposal, and provides further evidence for it. Unlike the case of closed strings, where the emergent terms are kinetic terms in the action, for these open strings it is tree-level potential terms which are emergent. This provides a first quantitative example of the proposal that classical tree-level potentials in string theory emerge from integrating out co-dimension one states.

On Calabi‐Yau Manifolds at Strong Topological String Coupling

AbstractIt was recently shown that integrating out M2 states on Calabi‐Yau manifolds captures non‐perturbative topological string physics in the free energy. In this note, It has been shown that the resulting expression manifests a certain duality symmetry: the free energy at strong string coupling is equal to the Calabi‐Yau period at weak string coupling. The duality yields the appropriate prescription for completing the integrating out in the ultraviolet.

Anomalous U(1) gauge bosons and string physics at the forward physics facility

We show that experiments at the Forward Physics Facility, planned to operate near the ATLAS interaction point during the LHC high-luminosity era, will be able to probe predictions of Little String Theory by searching for anomalous U(1) gauge bosons living in the bulk. The interaction of the abelian broken gauge symmetry with the Standard Model is generated at the one-loop level through kinetic mixing with the photon. Gauge invariant generation of mass for the U(1) gauge boson proceeds via the Higgs mechanism in spontaneous symmetry breaking, or else through anomaly-cancellation appealing to Stückelberg-mass terms. We demonstrate that FASER2 will be able to probe string scales over roughly two orders of magnitude: 105≲Ms/TeV≲107.

Rindler Physics on the String Worldsheet.

We construct the tensionless limit of bosonic string theory in terms of a family of worldsheets with increasing acceleration and show that the null string emerges in the limit of infinite acceleration when the Rindler horizon is hit. We discover a novel phenomenon we call null string complementarity, which gives two distinct observer-dependent pictures of the emergence of open string physics from closed strings in the tensionless limit. The closed string vacuum as observed by the inertial worldsheet turns into a D instanton in the tensionless limit, while in the complementary picture from the accelerated worldsheet, one sees the emergence of a D-25 brane. We finally discuss approaching the Rindler horizon through time evolution at constant acceleration and also show how an open string picture arises very naturally.

Nonabelian probes in holography

We find the range of parameters for which the open string physics on probe Dq-branes in the near-horizon geometry of Dp-branes decouples from gravity, and is well-approximated by a (q+1)-dimensional supersymmetric Yang-Mills-Higgs theory on a rigid curved spacetime. We study the vacua of these theories, which include moduli spaces of instantons, monopoles, and vortices. This intricate structure is made possible through couplings to the background Ramond-Ramond flux. The probe brane theories we study provide holographic descriptions of defects in dual field theories.

String dualities and empirical equivalence

String dualities establish empirical equivalence between theories that often look entirely different with respect to their basic ontology and physical structure. Therefore, they represent a particularly interesting example of empirical equivalence in physics. However, the status of duality relations in string physics differs substantially from the traditional understanding of the role played by empirical equivalence. The paper specifies three important differences and argues that they are related to a substantially altered view on the underdetermination of theory building.

A nonabelian particle–vortex duality

We define a nonabelian particle–vortex duality as a 3-dimensional analogue of the usual 2-dimensional worldsheet nonabelian T-duality. The transformation is defined in the presence of a global SU(2) symmetry and, although derived from a string theoretic setting, we formulate it generally. We then apply it to so-called “semilocal strings” in an SU(2)G×U(1)L gauge theory, originally discovered in the context of cosmic string physics.

Fivebranes, dualities and non-geometry

In this contribution we would like to review and clarify the relation between a large class of extended objects in string theory and a set of generalized fluxes appearing in string compactifications. The main focus of this work is on the interplay between branes and dualities, which leads to novel states which are important for string physics. The main result that we would like to describe is the coupling of these new branes to the background fields of string theory and the exact correspondence between them and generalized stringy fluxes.

TeV-Scale Strings

This review discusses the status of string physics where the string tension is around the TeV scale. It covers model-building basics for perturbative strings, based on D-brane configurations. The effective low-energy physics description of such string constructions is analyzed: how anomaly cancellation is implemented, how fast proton decay is avoided, and how D-brane models lead to additional Z′ particles. This review also discusses direct search bounds for strings at the TeV scale, as well as theoretical issues with model building related to flavor physics and axions.

LHC phenomenology and cosmology of string-inspired intersecting D-brane models

We discuss the phenomenology and cosmology of a Standardlike Model inspired by string theory, in which the gauge fields are localized on D-branes wrapping certain compact cycles on an underlying geometry, whose intersection can give rise to chiral fermions. The energy scale associated with string physics is assumed to be near the Planck mass. To develop our program in the simplest way, we work within the construct of a minimal model with gauge-extended sector $U(3{)}_{B}\ifmmode\times\else\texttimes\fi{}Sp(1{)}_{L}\ifmmode\times\else\texttimes\fi{}U(1{)}_{{I}_{R}}\ifmmode\times\else\texttimes\fi{}U(1{)}_{L}$. The resulting $U(1)$ content gauges the baryon number $B$, the lepton number $L$, and a third additional Abelian charge ${I}_{R}$ which acts as the third isospin component of an $SU(2{)}_{R}$. All mixing angles and gauge couplings are fixed by rotation of the $U(1)$ gauge fields to a basis diagonal in hypercharge $Y$ and in an anomaly-free linear combination of ${I}_{R}$ and $B\ensuremath{-}L$. The anomalous ${Z}^{\ensuremath{'}}$ gauge boson obtains a string scale St\"uckelberg mass via a 4D version of the Green-Schwarz mechanism. To keep the realization of the Higgs mechanism minimal, we add an extra $SU(2)$ singlet complex scalar, which acquires a VEV and gives a TeV-scale mass to the nonanomalous gauge boson ${Z}^{\ensuremath{'}\ensuremath{'}}$. The model is fully predictive and can be confronted with dijet and dilepton data from LHC8 and, eventually, LHC14. We show that ${M}_{{Z}^{\ensuremath{'}\ensuremath{'}}}\ensuremath{\approx}3--4\text{ }\text{ }\mathrm{TeV}$ saturates current limits from the CMS and ATLAS Collaborations. We also show that for ${M}_{{Z}^{\ensuremath{'}\ensuremath{'}}}\ensuremath{\lesssim}5\text{ }\text{ }\mathrm{TeV}$, LHC14 will reach discovery sensitivity $\ensuremath{\gtrsim}5\ensuremath{\sigma}$. After that, we demonstrate in all generality that ${Z}^{\ensuremath{'}\ensuremath{'}}$ milliweak interactions could play an important role in observational cosmology. Finally, we examine some phenomenological aspects of the supersymmetric extension of the D-brane construct.

Geometry of open strings ending on backreacting D3-branes

We investigate open string theory on backreacting D3-branes using a spacetime approach. We study in detail the half-BPS supergravity solutions describing open strings ending on D3-branes, in the near horizon of the D3-branes. We recover quantitatively several non-trivial features of open string physics including the appearance of D3-brane spikes, the polarization of fundamental strings into D5-branes, and the Hanany-Witten effect. Finally we detail the computation of the gravitational potential between two open strings, and contrast it with the holographic computation of Wilson lines. We argue that the D-brane backreaction has a large influence on the low-energy gravity, which may lead to experimental tests for string theory brane-world scenarios.

ORIENTIFOLD STRING VACUA AND STRINGS AT THE LHC

We consider extensions of the Standard Model based on open strings ending on D-branes, with gauge bosons due to strings attached to stacks of D-branes and chiral matter due to strings stretching between intersecting D-branes. Assuming that the fundamental string mass scale is in the TeV range and the theory is weakly coupled, we discuss possible signals of string physics at the Large Hadron Collider (LHC).

LIGHTCONE 2011 Summary: applications of Light-Cone Coordinates to Highly Relativistic Systems

The 2011 workshop of the International Light Cone Advisory Committee (ILCAC), Inc., took place at Southern Methodist University (SMU) in Dallas, Texas, 23–27 May. These workshops have been held at least annually since 1990, focusing on the formal and phenomenological application of light-cone coordinates to nuclear, particle, and string physics, especially via light-front quantization of field theory. In short, the field studies physics from the viewpoint of an observer travelling at the speed of light, a frame of reference that has some unique kinematical and dynamical advantages. LIGHTCONE 2011 had about 50 physicists, featuring a total of 45 presentations (invited talks and posters). The workshop was purposely limited in size to avoid parallel sessions and to allow all participants to present if they wished. Each day began with a 1-h thematic keynote talk, followed by 1/2 h talks; a relatively large and well-attended poster session generated a lot of discussion. About half the working time of the conference was given to informal discussion. The daily themes of this workshop reflected the current interests of the field: AdS/CFT/QCD, Partons, Ab Initio Calculations, Nuclear and Many-Body, with the final morning covering a variety of topics. Presentations have therefore been divided into those themes in this volume. Many phenomenological applications to hadrons were discussed using holographic QCD, covariant constituent models, and chiral perturbation theory. Light-front holography, which maps AdS/QCD directly to LF QCD in physical space–time, was treated in talks by Brodsky and de Teramond. Discussions on the kinematic issues in extracting GPDs (B. Bakker and C. Ji) were highly relevant to the analysis of DVCS experiments at JLab and DESY. A number of new directions were presented at this workshop, including the phenomenology of multi-parton distributions (M. Diehl) and new computational methods, such as Light-cone Coupled-cluster (J. Hiller and S. Chabysheva) and Singular Value Decomposition (M. Weinstein). The most lively discussion centered on ‘in-hadron’ condensates, which eliminate the 45 orders of magnitude conflict between the cosmological constant and QCD (talks by Roberts, Brodsky, Tandy, Glazek) and reminiscent of the trivial vacuum of regulated light-front quantization. The in-hadron condensate idea, which seems at odds with the traditional idea of Lorentz invariant vacuumexpectation values associated to spontaneous symmetry breaking, was supported by some but vigorously opposed by other participants. Many other interesting presentations can be found in this volume—they are only half the story however, as discussions outside of the lecture room were as important.

LHC phenomenology of lowest massive Regge recurrences in the Randall-Sundrum orbifold

We consider string realizations of the Randall-Sundrum effective theory for electroweak symmetry breaking and explore the search for the lowest massive Regge excitation of the gluon and of the extra (color singlet) gauge boson inherent in D-brane constructions. In these curved backgrounds, the higher-spin Regge recurrences of standard model fields localized near the IR brane are warped down to close to the TeV range and hence can be produced at collider experiments. Assuming that the theory is weakly coupled, we make use of four gauge boson amplitudes evaluated near the first Regge pole to determine the discovery potential of LHC. We study the inclusive dijet mass spectrum in the central rapidity region $|{y}_{\mathrm{jet}}|<1.0$ for dijet masses $M\ensuremath{\ge}2.5\text{ }\text{ }\mathrm{TeV}$. We find that with an integrated luminosity of $100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, the $5\ensuremath{\sigma}$ discovery reach can be as high as 4.7 TeV. Observations of resonant structures in $pp\ensuremath{\rightarrow}\mathrm{\text{direct}}\ensuremath{\gamma}+\mathrm{\text{jet}}$ can provide interesting corroboration for string physics up to 3.0 TeV. We also study the ratio of dijet mass spectra at small and large scattering angles. We show that with the first ${\mathrm{fb}}^{\ensuremath{-}1}$ such a ratio can probe lowest-lying Regge states for masses $\ensuremath{\sim}2.5\text{ }\text{ }\mathrm{TeV}$.

Strings at the LHC

AbstractAssuming that the fundamental string mass scale is in the TeV range and the theory is weakly coupled, we discuss possible signals of string physics at the Large Hadron Collider (LHC).

STRING PHENOMENOLOGY AT THE LHC

We consider extensions of the standard model based on open strings ending on D-branes, with gauge bosons due to strings attached to stacks of D-branes and chiral matter due to strings stretching between intersecting D-branes. Assuming that the fundamental string mass scale is in the TeV range and the theory is weakly coupled, we review possible signals of string physics at the Large Hadron Collider.

Erratum: Quantization of the electromagnetic field outside static black holes and its application to low-energy phenomena [Phys. Rev. D63, 124008 (2001)

We discuss the Gupta-Bleuler quantization of the free electromagnetic field outside static black holes in the Boulware vacuum. We use a gauge which reduces to the Feynman gauge in Minkowski spacetime. We also discuss its relation with gauges used previously. Then we apply the low-energy sector of this field theory to investigate some low-energy phenomena. First, we discuss the response rate of a static charge outside the Schwarzschild black hole in four dimensions. Next, motivated by string physics, we compute the absorption cross sections of low-energy plane waves for the Schwarzschild and extreme Reissner-Nordstr\"om black holes in arbitrary dimensions higher than three.

LHC phenomenology for string hunters

We consider extensions of the standard model based on open strings ending on D-branes, with gauge bosons due to strings attached to stacks of D-branes and chiral matter due to strings stretching between intersecting D-branes. Assuming that the fundamental string mass scale is in the TeV range and the theory is weakly coupled, we discuss possible signals of string physics at the Large Hadron Collider (LHC). In previous works, direct channel excitations of Regge recurrences in parton–parton scattering supplied the outstanding new signature. The present work considers the deviation from standard model expectations for the 4-fermion processes q q → q q and q q ′ → q q ′ , in which the s-channel excitation of string resonances is absent. In this case, we find that Kaluza–Klein recurrences at masses somewhat less than the string scale generate effective 4-fermion contact terms which can significantly enhance the dijet R ratio above its QCD value of about 0.6. The simultaneous observation of a nearby resonant structure in the dijet mass spectrum would provide a “smoking gun” for TeV scale string theory. In this work, we also show that (1) for M string < 3.5 TeV , the rates for various topologies arising from the p p → Z 0 + jet channel could deviate significantly from standard model predictions and (2) that the sizeable cross sections for Regge recurrences can allow a 6 σ discovery for string scales as large as 3 TeV after about 1 year of LHC operation at s = 10 TeV and ∫ L d t ∼ 100 pb − 1 .

String theory at LHC using top quarks from string balls

According to string theory, string ball is a highly excited long string which decays to standard model particles at the Hagedorn temperature with thermal spectrum. If there are extra dimensions, the string scale can be ~ TeV, and we should produce string balls at CERN LHC. In this paper we study top quark production from string balls at LHC and compare with the parton fusion results at NNLO using pQCD. We find significant top quark production from string balls at LHC which is comparable to standard model pQCD results. We also find that d?/dpT of top quarks from string balls does not decrease significantly with increase in pT, whereas it deceases sharply in case of standard model pQCD scenario. Hence, in the absence of black hole production at LHC, an enhancement in top quark cross section and its abnormal pT distribution can be a signature of TeV scale string physics at LHC. String theory is also studied at LHC via string Regge excitations in the weak coupling limit in model independent framework. Since massive quark production amplitude is not available in string Regge excitations scenario, we compute massless quark production in string Regge excitations scenario and make a clear comparison with that produced from string balls at LHC for a given luminosity.

Dijet Signals for Low Mass Strings at the Large Hadron Collider

Assuming that the fundamental string mass scale is in the TeV range and the theory is weakly coupled, we discuss possible signals of string physics at the Large Hadron Collider (LHC). In D-brane constructions, the dominant contributions to full-fledged string amplitudes for all the common QCD parton subprocesses leading to dijets are completely independent of the details of compactification, and can be evaluated in a parameter-free manner. We make use of these amplitudes evaluated near the first resonant pole to determine the discovery potential of LHC for the first Regge excitations of the quark and gluon. Remarkably, the reach of LHC after a few years of running can be as high as 6.8 TeV. Even after the first 100 pb(-1) of integrated luminosity, string scales as high as 4.0 TeV can be discovered. Data on pp-->directgamma + jet can provide corroboration for string physics at scales as high as 5 TeV.