Open String Research Articles

Strong coupling expansion of circular Wilson loops and string theories in AdS5 \xd7 S5 and AdS4 \xd7 CP3

We revisit the problem of matching the strong coupling expansion of the frac{1}{2} BPS circular Wilson loops in mathcal{N} = 4 SYM and ABJM gauge theories with their string theory duals in AdS5× S5 and AdS4× CP3, at the first subleading (one-loop) order of the expansion around the minimal surface. We observe that, including the overall factor 1/gs of the inverse string coupling constant, as appropriate for the open string partition function with disk topology, and a universal prefactor proportional to the square root of the string tension T, both the SYM and ABJM results precisely match the string theory prediction. We provide an explanation of the origin of the sqrt{T} prefactor based on special features of the combination of one-loop determinants appearing in the string partition function. The latter also implies a natural generalization Zχ ∼ ( sqrt{T}/{g}_{mathrm{s}} )χ to higher genus contributions with the Euler number χ, which is consistent with the structure of the 1/N corrections found on the gauge theory side.

Classical de Sitter solutions in three dimensions without tachyons?

We continue the study of compactifications of massive IIA supergravity on G2 orientifolds and demonstrate that breaking supersymmetry with anti-D2 and anti-D6 sources leads to 3d theories for which the typical tachyons haunting classical dS solutions can be absent. However for a concrete torus example the meta-stable dS window disappears after a quantization of fluxes and charges. We discuss the prospects of more general G2 compactifications and argue that they could potentially alleviate the tachyon problem by introducing larger tadpole numbers and warped throats. However, exactly those ingredients then seem to push the vacuum towards the brink of perturbative brane–flux decay in the open string sector. This is either a remarkable illustration of the no-dS swampland conjecture or such vacua live in very difficult to control regions of parameter space.

Supersymmetric indices on I × T2, elliptic genera and dualities with boundaries

We study three dimensional N=2 supersymmetric theories on I×M2 with 2d N=(0,2) boundary conditions at the boundaries ∂(I×M2)=M2⊔M2, where M2=C or T2. We introduce supersymmetric indices of three dimensional N=2 theories on I×T2 that couple to elliptic genera of 2d N=(0,2) theories at the two boundaries. We evaluate the I×T2 indices in terms of supersymmetric localization and study dualities on the I×M2. We consider the dimensional reduction of I×T2 to I×S1 and obtain the localization formula of 2d N=(2,2) supersymmetric indices on I×S1. We illustrate computations of open string Witten indices based on gauged linear sigma models. Correlation functions of Wilson loops on I×S1 agree with Euler pairings in the geometric phase and also agree with cylinder amplitudes for B-type boundary states of Gepner models in the Landau-Ginzburg phase.

A global perspective on parental stress in the neonatal intensive care unit: a meta-analytic study.

The Parental Stressor Scale: Neonatal Intensive Care Unit (PSS:NICU) is a well-validated tool to assess different sources of stress in parents during the NICU hospitalization of their infant. The present meta-analytic study assessed the relative impact of different NICU-related sources of parental stress in a pool of studies conducted in a wide set of different countries. Also, differences in stress levels by parent gender and country, as well as the impact of infants' neonatal characteristics and clinical conditions were explored. Records were searched on PubMed, Scopus, and Web of Science (January 1993-December 2019). A purposive open search string was adopted: ["PSS:NICU"] OR ["PSS-NICU"] OR ["Parental Stressor Scale"]. A multiple random-effect meta-analysis was conducted on data from 53 studies extracted by independent coders. Parental role alteration emerged as the greatest source of stress for both mothers and fathers. Mothers reported higher stress levels compared to fathers. A significant difference emerged only for the subscale related to sights and sounds physical stimuli. No significant effects of infants' neonatal characteristics (gestational age, birth weight) and clinical conditions (comorbidities) emerged. A marginal positive effect of NICU length of stay emerged on the global level of parents' stress. The current meta-analysis underlines that parental stress related to NICU admission is a worldwide healthcare issue. Immediate and tailored support to parents after the birth of their at-risk infant should be prioritized to reduce parental stress and to promote mothers and fathers' emotional well-being and new-born neurodevelopmental outcomes.

String Two-Point Amplitude Revisited by Operator Formalism

Although one has trusted that the tree-level string two-point amplitudes vanish due to the infinite volume of residual gauge symmetry, recently the non-zero string two-point amplitudes have been pointed out in the path integral formalism. We consider them in the operator formalism. We have succeeded in obtaining the non-zero two-point amplitude in an open bosonic string theory by introducing a novel mostly BRST exact operator. We then show some trials in a closed string theory.

Meromorphic continuation of Koba-Nielsen string amplitudes

In this article, we establish in a rigorous mathematical way that Koba-Nielsen amplitudes defined on any local field of characteristic zero are bona fide integrals that admit meromorphic continuations in the kinematic parameters. Our approach allows us to study in a uniform way open and closed Koba-Nielsen amplitudes over arbitrary local fields of characteristic zero. In the regularization process we use techniques of local zeta functions and embedded resolution of singularities. As an application we present the regularization of p-adic open string amplitudes with Chan-Paton factors and constant B-field. Finally, all the local zeta functions studied here are partition functions of certain 1D log-Coulomb gases, which shows an interesting connection between Koba-Nielsen amplitudes and statistical mechanics.

The interaction of glueball and heavy-light flavoured meson in holographic QCD

We construct the D4/D8 brane configuration in the Witten–Sakai–Sugimoto model by introducing a pair of heavy flavour brane with a heavy-light open string. The multiplets created by the heavy-light string acquire mass due to the finite separation of the heavy and light flavour branes thus they could be identified as the heavy-light meson fields in this model. On the other hand the glueball field is identified as the gravitational fluctuations carried by the close string in the bulk, so this model is able to describe the interaction of glueball and heavy-light meson through the open-close string interaction in gauge-gravity duality. We explicitly derive the effective action for the various glueballs and heavy-light mesons then numerically evaluate the associated lowest coupling constants. Afterwards the decay/production widths of various glueballs involving the lowest heavy-light meson, which is identified as D^{0} meson, are calculated by using our effective action which might be remarkable to theoretically study the charm oscillation e.g. D^{0}-{bar{D}}^{0}, B_{s}-{bar{B}}_{s} decay/production in hadron physics. This work extends the previous investigations of glueball in holographic QCD and it is also a further prediction of glueball-meson interaction.

M-theory and orientifolds

We construct the M-Theory lifts of type IIA orientifolds based on K3-fibred Calabi-Yau threefolds with compatible involutions. Such orientifolds are shown to lift to M-Theory on twisted connected sum G2 manifolds. Beautifully, the two building blocks forming the G2 manifold correspond to the open and closed string sectors. As an application, we show how to use such lifts to explicitly study open string moduli. Finally, we use our analysis to construct examples of G2 manifolds with different inequivalent TCS realizations.

Open string QED meson description of the X17 particle and dark matter

As a quark and an antiquark cannot be isolated, the intrinsic motion of a composite qoverline{q} system in its lowest-energy states lies predominantly in 1+1 dimensions, as in an open string with the quark and the antiquark at its two ends. Accordingly, we study the lowest-energy states of an open string qoverline{q} system in QCD and QED in 1+1 dimensions. We show that π0, η, and η′ can be adequately described as open string qoverline{q} QCD mesons. By extrapolating into the qoverline{q} QED sector in which a quark and an antiquark interact with the QED interaction, we find an open string isoscalar I(Jπ) = 0(0−) QED meson state at 17.9±1.5 MeV and an isovector (I(Jπ) = 1(0−), I3 = 0) QED meson state at 36.4±3.8 MeV. The predicted masses of the isoscalar and isovector QED mesons are close to the masses of the hypothetical X17 and E38 particles observed recently, making them good candidates for these particles. The decay products of QED mesons may show up as excess e+e− and γγ pairs in the anomalous soft photon phenomenon associated with hadron productions in high-energy hadron-proton collisions and e+-e− annihilations. Measurements of the invariant masses of excess e+e− and γγ pairs will provide tests for the existence of the open string qoverline{q} QED mesons. An assembly of gravitating QED mesons are expected to emit electron-positron pairs and/or gamma rays and their decay energies and lifetimes will be modified by their gravitational binding energies. Consequently, a self-gravitating isoscalar QED meson assembly whose mass M and radius R satisfy (M/M⨀)/(R/R⨀) ≳ 2 4.71 × 105 will not produce electron-positron pairs nor gamma rays and may be a good candidate for the primordial dark matter.

Quantum stability in open string theory with broken supersymmetry

We consider the 1-loop effective potential in type I string theory compactified on a torus, with supersymmetry broken by the Scherk-Schwarz mechanism. At fixed supersymmetry breaking scale M, and up to exponentially suppressed terms, we show that the potential admits local minima of arbitrary sign, in dimension d ≤ 5. While the open string Wilson lines are massive, the closed string moduli are flat directions. In a T-dual picture, the relevant backgrounds involve isolated ½-branes, whose positions are frozen on orientifold planes, thus decreasing the rank of the gauge group, and introducing massless fermions in fundamental representations.

D-instanton perturbation theory

D-instanton world-volume theory has open string zero modes describing collective coordinates of the instanton. The usual perturbative amplitudes in the D-instanton background suffer from infra-red divergences due to the presence of these zero modes, and the usual approach of analytic continuation in momenta does not work since all open string states on a D-instanton carry strictly zero momentum. String field theory is well-suited for tackling these issues. However we find a new subtlety due to the existence of additional zero modes in the ghost sector. This causes a breakdown of the Siegel gauge, but a different gauge fixing consistent with the BV formalism renders the perturbation theory finite and unambiguous. At each order, this produces extra contribution to the amplitude besides what is obtained from integration over the moduli space of Riemann surfaces.

The scattering amplitude of stringy hadrons: strings with opposite charges on their endpoints

In this note we describe hadrons: mesons and baryons as strings with electric charges on their endpoints. We consider here only the neutral system with opposite charges, coupled to an external constant electromagnetic field. We derive certain classical solutions including rotating folded open strings. We write down the mode expansion and canonically quantize the system. The OPEs associated with such strings are determined. We rederive the non-commutativity of the zero modes and the fact that the charges modify the spacetime metric. We show that the quantum worldsheet energy momentum tensor on the boundary is affected by the endpoint charges and differs from the corresponding Noether current. We determine the generalization of the Veneziano scattering amplitude for such strings in the critical dimension. Phenomenological implications are addressed and in particular we show that the external magnetic field can be tuned so that the amplitude vanishes for particular kinematic setups. We discuss the generalization of such strings to non-critical four dimensional spacetime. In particular we renormalize the divergence of the Polchinski-Strominger effective action associated with the rotating folded string.

Brane with transverse rotation and background fields: boundary state and tachyon condensation

The boundary state corresponding to the Dp-brane with a transverse rotation in the presence of the Kalb–Ramond and tachyon background fields and a U(1) internal field will be constructed. We shall investigate effects of the open string tachyon condensation on this brane via its boundary state. We demonstrate that the background fields and transverse rotation cannot protect the brane against the collapse. Our calculations are in the context of the bosonic string theory.

Generalised Schwarzschild metric from double copy of point-like charge solution in Born-Infeld theory

We discuss possible application of the classical double copy procedure to construction of a generalisation of the Schwarzschild metric starting from an α′-corrected open string analogue of the Coulomb solution. The latter is approximated by a point-like charge solution of the Born-Infeld action, which represents the open string effective action for an abelian vector field in the limit when derivatives of the field strength are small. The Born-Infeld solution has a regular electric field which is constant near the origin suggesting that corrections from the derivative terms in the open string effective action may be small there. The generalization of the Schwarschild metric obtained by the double copy construction from the Born-Infeld solution looks non-singular but the corresponding curvature invariants still blow up at r=0. We discuss the origin of this singularity and comment on possible generalizations.

Discrete and continuous symmetries in monotone Floer theory

This paper studies the self-Floer theory of a monotone Lagrangian submanifold L of a symplectic manifold X in the presence of various kinds of symmetry. First we suppose L is K-homogeneous and compute the image of low codimension K-invariant subvarieties of X under the length-zero closed–open string map. Next we consider the group $$\mathrm {Symp}(X, L)$$ of symplectomorphisms of X preserving L setwise, and extend its action on the Oh spectral sequence to coefficients of arbitrary characteristic, incorporating its action on the classes of holomorphic discs. This imposes constraints on the differentials which force them to vanish in certain situations. These techniques are combined to study a family of homogeneous Lagrangians in products of projective spaces, which exhibit some unusual properties.

Time evolution of entanglement entropy in holographic FLRW cosmologies

To understand the time-dependent quantum correlation in expanding universes, we study the time-dependent entanglement entropy in the braneworld model. If we take into account a generalized string cloud geometry caused by uniformly distributed open strings, cosmologies on the braneworld result in the standard Friedmann-Lema\^{i}tre-Robertson-Walker cosmologies with various matter contents. On the dual field theory side, open strings are reinterpreted as a fundamental matter, while the black hole mass corresponds to the excitation energy of massless gauge bosons. In this work, we show how the string cloud geometry is matched to various braneworld cosmologie,s for example, eternal inflation, radiation-, and matter-dominated universes. Then, we investigate how the entanglement entropy evolves in those expanding universes.

Stringy excited baryons in holographic quantum chromodynamics

Abstract We analyze excited baryon states using a holographic dual of quantum chromodynamics that is defined on the basis of an intersecting D4/D8-brane system. Studies of baryons in this model have been made by regarding them as a topological soliton of a gauge theory on a five-dimensional curved spacetime. However, this allows one to obtain only a certain class of baryons. We attempt to present a framework such that a whole set of excited baryons can be treated in a systematic way. This is achieved by employing the original idea of Witten, which states that a baryon is described by a system composed of $N_c$ open strings emanating from a baryon vertex. We argue that this system can be formulated by an Atiyah–Drinfeld–Hitchin–Manin-type matrix model of Hashimoto–Iizuka–Yi together with an infinite tower of the open string massive modes. Using this setup, we work out the spectra of excited baryons and compare them with the experimental data. In particular, we derive a formula for the nucleon Regge trajectory assuming that the excited nucleons lying on the trajectory are characterized by the excitation of a single open string attached on the baryon vertex.

Open-string non-associativity in an R-flux background

We derive the commutation relations for open-string coordinates on D-branes in non-geometric background spaces. Starting from D0-branes on a three-dimensional torus with H -flux, we show that open strings with end points on D3-branes in a three-dimensional R-flux background exhibit a non-associative phase-space algebra, which is similar to the non-associative R-flux algebra of closed strings. Therefore, the effective open-string gauge theory on the D3-branes is expected to be a non-associative gauge theory. We also point out differences between the non-associative phase space structure of open and closed strings in non-geometric backgrounds, which are related to the different structure of the world-sheet commutators of open and closed strings.

On the origin of divergences in time-dependent orbifolds

We consider time-dependent orbifolds in String Theory and we show that divergences are not associated with a gravitational backreaction since they appear in the open string sector too. They are related to the non existence of the underlying effective field theory as in several cases fourth and higher order contact terms do not exist. Since contact terms may arise from the exchange of string massive states, we investigate and show that some three points amplitudes with one massive state in the open string sector are divergent on the time-dependent orbifolds. To check that divergences are associated with the existence of a discrete zero eigenvalue of the Laplacian of the subspace with vanishing volume, we construct the Generalized Null Boost Orbifold where this phenomenon can be turned on and off.

Comments on open string with 'massive' boundary term.

We discuss possible definition of open string path integral in the presence of additional boundary couplings corresponding to the presence of masses at the ends of the string. These couplings are not conformally invariant implying that as in a non-critical string case one is to integrate over the one-dimensional metric or reparametrizations of the boundary. We compute the partition function on the disc in the presence of an additional constant gauge field background and comment on the structure of the corresponding scattering amplitudes.