Type I String Research Articles

Higher-point gauge-theory couplings of massive spin-2 states in four-dimensional string theories

We explicitly compute the Neveu-Schwarz sector conventional type-I superstring tree-level amplitudes at five points after compactifying to 4D, express the QFT building block in the helicity basis, and give several attempts toward arbitrary n points. More specifically, we consider the interaction of one first excited level and otherwise massless states of conventional type-I superstrings, where the four-dimensional states can, for instance, be realized via D3 branes. We construct the amplitude by using the Berends-Giele currents. From the recursion of Berends-Giele currents, we can generate the higher point amplitude. We also apply the BCFW recursion with massive external legs shifted and get the amplitude for arbitrary n points. Published by the American Physical Society 2024

Bootstrapping string theory EFT

We study the space of open string effective field theories by combining the constraint of unitarity and monodromy relations for the four-point amplitude. The latter is a reflection of an underlying disk correlator with singularities at the boundary. By assuming maximal susy the resulting bootstrap isolates Wilson coefficients to at least 10−4 of the Type-I superstring. Furthermore, utilizing our geometric approach, we obtain the critical dimension of 10 from the low energy coefficients alone. Remarkably, relaxing SUSY but requiring the massless states to carry four-dimensional helicities, the Wilson coefficients are again constrained to superstring values within 10−4. Thus we conclude that type-I string theory is the unique solution to the monodromy bootstrap with either maximal susy or vector external states. We also introduce Tachyons to the bootstrap and demonstrate for the scattering of external vectors, the bosonic and superstring span the allowed region. Allowed regions for closed string effective field theories are obtained by implementing the KLT relations.

Higher Dimensional Bianchi Type-I Cosmological Models With Massive String in General Relativity

Here we studied Bianchi type-I cosmological models with massive strings in general relativity in five dimensional space time. Out of the two different cases obtained here, one case leads to a five dimensional Bianchi type-I string cosmological model in general relativity while the other yields the vacuum Universe in general relativity in five dimensional space time. The physical and geometrical properties of the model Universe are studied and compared with the present day’s observational findings. It is observed that our model is anisotropic, expanding, shearing, and decelerates at an early stage and then accelerates at a later time. The model expands along x, y, and z axes and the extra dimension contracts and becomes unobservable at t → ∞. We also observed that the sum of the energy density (ρ) and the string tension density (λ) vanishes (ρ + λ = 0).

Higher dimensional Bianchi type-I string cosmological model in f(R) theory of gravity

In this paper, we have studied Bianchi type-I string cosmological model by combining Kaluza-Klein (KK) theory and f(R) theory of gravity which is an extension of 5-dimensional KK string cosmological models. We have used equation of state in the form of p-string or Takabayasi string given by ρ=(1+ω)λ, where ρ and λ denote the rest density of energy cloud of strings, and the tension density of the system of strings, respectively and ω is a constant. In order to get physically significant and viable solution various forms of the function f(R) are assumed, in this paper we assume f(R)=R+αR2 (e.g. Astashenok et al. (2017) [1]), where α is real number. Some physical and geometrical properties of the model are also discussed.

Five dimensional Bianchi type-I string cosmological model with electromagnetic field

In this paper we defined the five dimensional Bianchi type-I string cosmological models with electromagnetic field. Here we considered that the energy momentum tensor is equal to the sum of the energy density, tension density and electromagnetic field. In order to get determinate solutions of the Einstein's field equations, we assume the average scale factor as a connecting function of time. Some physical and kinematical parameters are also discussed.

Higher Dimensional Bianchi Type-I String Cosmological Model in f(R) Theory of Gravity

The field equations of Kaluza-Klein (KK) theory have been used in the area of cosmology. The researchers have scrutinized KK theory in the existence of cosmic string as a source in f(R) theory of gravity which is an extension of 5-dimensional KK string cosmological models. Certain features, physical and geometrical properties of the model are also investigated.

Higher Dimensional LRS Bianchi Type-I String Cosmological Model with Bulk Viscosity in General Relativity

Objective: To present a new solution to the field equations obtained for higher dimensional LRS Bianchi type-I universe generated by means of a cloud of strings with particles connected to them with bulk viscosity in general relativity. Methods: To obtain the solutions of field equations of higher dimensional LRS Bianchi type-I universe we consider that the shear scalar of the model is proportional to the scalar expansion of the model (saq ), which leads to, c=b^n. The physical and geometrical behaviors of the model universe are studied by comparing with the present cosmological scenario and observations. Findings: It is observed that our model is anisotropic, expanding and decelerates at early stage and then accelerates in late universe giving the inflation model universe. Novelty: We obtained new solution to the field equations for higher dimensional LRS Bianchi type-I generated by means of a cloud of strings with bulk viscous fluid in general relativity. Keywords: LRS Bianchi TypeI Metric; Bulk Viscous Fluid; Strings

Five dimensional Bianchi type-I string cosmological model with electromagnetic field

In this paper we defined the five dimensional Bianchi type-I string cosmological models with electromagnetic field. Here we considered that the energy momentum tensor is equal to the sum of the energy density, tension density and electromagnetic field. In order to get determinate solutions of the Einstein's field equations, we assume the average scale factor as a connecting function of time. Some physical and kinematical parameters are also discussed.

Locally rotationally symmetric Bianchi type-I string cosmological models in f(R) theory of gravity

This study deals with spatially homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi type-I universe with cosmic string source in the framework of [Formula: see text] theory of gravity [S. Capozziello, S. Carloni and A. Troisi, Quintessence without scalar fields, Recent Res. Dev. Astron. Astrophys. 1 (2003), 625; S. Nojiri and S. D. Odintsov, Modified gravity with negative and positive powers of curvature: Unification of inflation and cosmic acceleration, Phys. Rev. D 68 (2003) 123512]. Solving the field equations using (i) relation between metric potentials, (ii) power law relation between [Formula: see text] and average scale factor [Formula: see text] and (iii) equations of state for string models we have presented Takabayasi [T. Takabayasi, Quantum Mechanics Determinism, Causality, and Particles (Springer, Berlin, 1976)], Nambu [P. S. Letelier, String cosmologies, Phys. Rev. D 28 (1983) 2414–2419] and Reddy [D. R. K. Reddy, A string cosmological model in a scalar–Tensor theory of gravitation, Astrophys. Space Sci. 286 (2003) 359–363] string cosmological models. The dynamical parameters of our models are determined and their physical behavior is discussed. The most interesting result about the models is that the anisotropic effects are wiped out at late times.

Bianchi Type-I String Dust Models with Bulk Viscosity in Lyra Geometry

In the present study, we have investigated string dust models with bulk viscosity in Lyra geometry taking Bianchi type-I space–time as a source. To get the determinate model, we have assumed the conditions $$ \sigma_{1}^{1} \,\alpha \,\theta \,{\text{and}}\,\zeta \,\theta = \,{\text{constant}} $$ where $$ \sigma_{1}^{1} $$ the component of shear tensor $$ (\sigma_{\text{i}}^{\text{j}}) ,\,\theta$$ the expansion in the model, ζ the coefficient of bulk viscosity. We observed that string cosmological models are possible in the frame work of Lyra manifold with one of shear tensor component bears the constant ratio to expansion. The models satisfy reality condition in presence and absence of bulk viscosity. The anisotropy is maintained due to the presence of strings. The models in presence of bulk viscosity has point type singularity while in absence of bulk viscosity, the model represents cigar type singularity. The displacement vector of Lyra geometry is initially large but decreases with time in presence and absence of bulk viscosity. The other physical aspects are also discussed.

Anisotropic Bianchi Type-I and Type-II Bulk Viscous String Cosmological Models Coupled with Zero Mass Scalar Field

The LRS Bianchi type-I and type-II string cosmological models are studied when the source for the energy momentum tensor is a bulk viscous stiff fluid containing one dimensional strings together with zero-mass scalar field. We have obtained the solutions of the field equations assuming a functional relationship between metric coefficients when the metric is Bianchi type-I and constant deceleration parameter in case of Bianchi type-II metric. The physical and kinematical properties of the models are discussed in each case. The effects of Viscosity on the physical and kinematical properties are also studied.

Type-I cosmic-string network

We study the network of Type-I cosmic strings using the field-theoretic numerical simulations in the Abelian-Higgs model. For Type-I strings, the gauge field plays an important role, and thus we find that the correlation length of the strings is strongly dependent upon the parameter \beta, the ratio between the self-coupling constant of the scalar field and the gauge coupling constant, namely, \beta=\lambda/2e^2. In particular, if we take the cosmic expansion into account, the network becomes densest in the comoving box for a specific value of \beta for \beta<1.

Bianchi type-I string cosmological model in the presence of a magnetic field: classical versus loop quantum cosmology approaches

A Bianchi type-I cosmological model in the presence of a magnetic flux along a cosmological string is considered. The first objective of this study is to investigate Einstein equations using a tractable assumption usually accepted in the literature. Quantum effects of the present cosmological model are examined in the framework of loop quantum cosmology. Finally we draw a parallel between the classical and quantum approaches.

Bianchi Type-I String Cosmological Model with Bulk Viscosity and Time-Dependent Λ term

Einstein field equations with the cosmological constant is considered in the presence of bulk viscosity in a Bianchi type-I universe. Solutions of the field equations are obtained by assuming the following conditions: the bulk viscosity is proportional to the expansion scalar ξ ∝ θ; the expansion scalar is proportional to shear scalar θ ∝ σ; and Λ is proportional to the Hubble parameter Λ ∝ H. The corresponding interpretations of the cosmological solutions are also discussed.

Bianchi type-I massive string magnetized barotropic perfect fluid cosmological model in bimetric theory

Bianchi type-I massive string cosmological model for perfect fluid distribution in the presence of magnetic field is investigated in Rosen’s [Gen. Relativ. Gravit. 4, 435 (1973)] bimetric theory of gravitation. To obtain the deterministic model in terms of cosmic time, we have used the condition A = (BC) n , where n is a constant, between the metric potentials. The magnetic field is due to the electric current produced along the x-axis with infinite electrical conductivity. Some physical and geometrical properties of the exhibited model are discussed and studied.

BIANCHI TYPE-I STRING DUST COSMOLOGICAL MODELS IN LYRA GEOMETRY

Bianchi type-I string cosmological models with time dependent gauge function (β) within the framework of Lyra geometry is presented. To get the deterministic model of the universe, we assume that the eigenvalue [Formula: see text] of shear tensor [Formula: see text] is proportional to the expansion (θ). This leads to A = (BC)nwhere A, B, C are metric potential and n is a constant. The physical and geometrical aspects of the model are discussed in detail. In a special case, the behavior of the model in terms of cosmic time t for [Formula: see text] is also discussed.

Bianchi type-I string cosmological model in the presence of a magnetic flux: exact and qualitative solutions

Abstract A Bianchi type-I cosmological model in the presence of a magnetic flux along a cosmological string is investigated. The objective of this study is to generate solutions to the Einstein equations using a few tractable assumptions usually accepted in the literature. The analytical solutions are supplemented with numerical and qualitative analysis. In the frame of the present model the evolution of the Universe and other physical aspects are discussed.

Anisotropic universe with cosmic strings and bulk viscosity

Spatially homogeneous and anisotropic LRS Bianchi type-I string cosmological models are studied in the frame work of general relativity when the source for the energy momentum tensor is a bulk viscous fluid containing one dimensional strings. A barotropic equation of state for the pressure and density is assumed to get determinate solutions of the field equations. The bulk viscous pressure is assumed to be proportional to the energy density. The physical and kinematical properties of the models are discussed. The role of bulk viscosity in getting an inflationary phase in the universe is studied.

Bulk viscous barotropic magnetised string cosmological models

Spatially homogeneous and anisotropic LRSBianchi type-I string cosmological models are studied in the frame work of general relativity when the source for the energy momentum tensor is a bulk viscous fluid containing one dimensional strings embedded in a magnetic field. A barotropic equation of state for the pressure and density is assumed to get determinate solutions of the field equations. The bulk viscous pressure is assumed to be proportional to the energy density. The effects of viscosity and electromagnetic field on the properties of the model are investigated. The role of bulk viscosity and electromagnetic field in getting an inflationary phase and in establishing a string phase in the universe is studied.

Time dependent viscous string cloud cosmological models

Bianchi type-I string cosmological models are studied in Saez-Ballester theory of gravitation when the source for the energy momentum tensor is a viscous string cloud coupled to gravitational field. The bulk viscosity is assumed to vary with time and is related to the scalar expansion. The relationship between the proper energy density ρ and string tension density λ are investigated from two different cosmological models.