Tachyon Scalar Field Research Articles

Constant-roll inflation with tachyon field in the holographic braneworld

Abstract We study inflation driven by the tachyon field in the holographic braneworld by assuming the second slow-roll parameter η is constant. The parameter η can be either defined by the tachyon scalar field and the Hubble parameter or by the Hubble parameter only. By assuming a constant η, we derive and numerically solve a differential equation for the Hubble expansion rate. We calculate numerically the scalar spectral index and the tensor-to-scalar ratio. We confront the results with the observational data and find some constraints on the free model parameters. The swampland conjectures are discussed in the context of the constant-roll inflation, with some accent on the holographic model.

Observational analysis on warm tachyon scalar field inflation via Woods–Saxon, valley hybrid, exponential, quartic, quasi exponential potentials

In this paper, we study the tachyon scalar field inflationary scenario considering FRW universe in context of modified Chaplygin gas model. For this purpose, we consider some well-known potential models such as Woods–Saxon potential , Valley hybrid potential, exponential potential, quartic potential, and Quasi exponential potential. We develop the relations for the number of e-folds N, slow roll parameters ϵ,η, scalar spectral index ns, scalar to tensor ratio r, and running scalar spectral index αs. To understand how the inflationary parameters behave, the planes of ns−r and ns−αs are plotted. Through these plotted planes, we check the consistency of these inflationary parameters for assumed potentials in light of the Planck 2018 observational data and compare our outcomes with these observation by incorporating observational contours. We found that the obtained results are compatible and consistent with the recent observational data.

The discreet charm of the discrete series in dS2

We study quantum field theories placed on a two-dimensional de Sitter spacetime (dS2) with an eye on the group-theoretic organization of single and multi-particle states. We explore the distinguished role of the discrete series unitary irreducible representation (UIR) in the Hilbert space. By employing previous attempts to realize these states in free tachyonic scalar field theories, we propose how the discrete series may contribute to the Källén–Lehmann decomposition of an interacting scalar two-point function. We also study BF gauge theories with SL(N,R) gauge group in dS2 and establish a relation between the discrete series UIRs and the operator content of these theories. Although present at the level of the operators, states carrying discrete series quantum numbers are projected out of the gauge-invariant Hilbert space. This projection is reminiscent of what happens for quantum field theories coupled to semiclassical de Sitter gravity, where we must project onto the subspace of de Sitter invariant states. We discuss how to impose the diffeomorphism constraints on local field-theory operators coupled to two-dimensional gravity in de Sitter, with particular emphasis on the role of contact terms. Finally, we discuss an SYK-type model with a random two-body interaction that encodes an infinite tower of discrete series operators. We speculate on its potential microscopic connection to the SL(N,R) BF theory in the large-N limit.

Probing the possibility of inflation realization with viscous cosmology

The research presented in the current article explores the potential for inflation realization in a cosmic environment with bulk viscosity using a tachyon scalar field. The present study rewrites the entropy conservation equation to take bulk viscosity into account. The work’s initial phase examined the behaviour of the equation of state parameter for logamediate, intermediate, and emergent scenarios within a framework of viscous cosmology having the viscosity coefficient in linear and polynomial forms. The study then focused on the relative dominance of the scalar field and potential for the tachyon scalar field in the presence of bulk viscosity for the different choices of scale factor and came to the conclusion that the prerequisite for the realization of inflation is met in the framework of bulk viscosity.

Extended constant-roll condition in non-canonical scalar field inflation

In this work, we apply the extended constant-roll condition to non-canonical scalar fields. We use in particular two types of non-canonical fields, namely, the tachyon field and the Dirac–Born–Infeld (DBI) field. We assume, in particular, that the tachyon scalar field satisfies the condition [Formula: see text], while the DBI scalar field satisfies the condition [Formula: see text]. We use the extended constant-roll condition to calculate the inflation indices for each of these non-canonical fields. In order to test the extended constant-roll condition, we use three types of potentials, namely chaotic potential, linear power-law potential and exponential potential, and choose power-law and exponential forms for the smooth function [Formula: see text]. It is then shown that the models under consideration are compatible with the latest Planck 2018 constraints.

Tachyonic dark energy in general relativity and teleparallel frameworks

This paper is intended to review the consequences of assuming tachyon scalar field as a candidate for dark energy from dynamical system technique and observational cosmology point of views. In the contexts of general relativity and teleparallel gravity, a variety of non-minimally coupled tachyon fields have been taken into consideration. These models provide us subclasses of scalar-tensor and scalar-torsion theories. This review covers the tachyonic chameleon, the non-minimally coupled tachyon field to the Gauss–Bonnet invariant and the tachyonic teleparallel dark energy models. Type Ia supernovae and baryonic acoustic oscillations datasets are the observational data that have been used to constrain the model parameters.

Lagrangian Reconstruction of Barrow Holographic Dark Energy in Interacting Tachyon Model

We consider a correspondence between the tachyon dark energy model and Barrow holographic dark energy (BHDE). The latter is a modified scenario based on the application of the holographic principle with Barrow entropy instead of the usual Bekenstein–Hawking one. We reconstruct the dynamics of the tachyon scalar field T in a curved Friedmann–Robertson–Walker universe both in the presence and absence of interactions between dark energy and matter. As a result, we show that the tachyon field exhibits non-trivial dynamics. In a flat universe, T˙2 must always be vanishing, independently of the existence of interaction. This implies ωD=−1 for the equation-of-state parameter, which in turn can be used for modeling the cosmological constant behavior. On the other hand, for a non-flat universe and various values of the Barrow parameter, we find that T˙2 decreases monotonically for increasing cos(Rh/a) and cosh(Rh/a), where Rh and a are the future event horizon and the scale factor, respectively. Specifically, T˙2≥0 for a closed universe, while T˙2<0 for an open one, which is physically not allowed. We finally comment on the inflation mechanism and trans-Planckian censorship conjecture in BHDE and discuss observational consistency of our model.

Swampland criteria of inflationary scalar field models with well-known potentials

We explore the swampland conjectures of quintessence and tachyon scalar field models in [Formula: see text] and Einstein gravities, respectively. In [Formula: see text] gravity, we consider cold and warm (by assuming generalized dissipative coefficient) inflationary scenarios and develop constraints on de-Sitter conjectures through Bekenstein entropy relation. In usual inflation, the de-Sitter conjecture constraint becomes constant (in terms of models constant parameters) which can be easily analyzed for its validity (i.e., [Formula: see text]). However, in warm inflation, we analyze the de-Sitter conjecture constraint through [Formula: see text], i.e., if [Formula: see text] then [Formula: see text] and hence we can obtain the required result. For evaluating this condition, we choose three well-known potentials such as monomial chaotic, hilltop and generalized exponential. It is observed that the condition [Formula: see text] satisfied for all three potentials in both regimes of dissipative coefficient for specific choice of constants. We also obtain satisfactory results of de-Sitter conjecture for tachyon and polytropic (with quintessence scalar field) in general relativity. We investigate the consistency of assumed potentials through inflationary parameters [Formula: see text] and [Formula: see text] comparing with Planck’s observational data 2018 and found them compatible with the recent observations.

Bulk Viscous Flat FLRW Model with Observational Constraints in f(T, B) Gravity

This paper investigates the impact of bulk viscosity within the framework of f(T,B) gravity. We consider a time-dependent viscosity model with a particular Hubble parameter expression. Here, we looked into the viability of well-motivated f(T,B) gravity model, which takes the form f=αlog(B)+βT, and has free parameters α and β. The 46 observational Hubble data (OHD) in the range 0≤z≤2.36 were used to constrain the model parameters to achieve the solution. We have used the Markov Chain Monte Carlo (MCMC) method to estimate model parameters and observe that the model appears to be in good agreement with the observations. In addition, we evaluate the effective viscous equation of state parameter for the f(T,B) model. We have examined the characteristics of different energy conditions for the stability analysis. The model is valid based on the positive behavior of null energy conditions (NEC), weak energy conditions (WEC), and dominant energy conditions (DEC); however, strong energy conditions (SEC) are in violation, suggesting that the universe is expanding faster. Our model was found in the quintom region. We also discussed how the tachyon scalar field corresponds to f(T,B) gravity.

Tsallis holographic dark energy scenario in viscous f(Q) gravity with tachyon field

This study investigates a bulk viscous fluid anisotropic cosmological model with [Formula: see text] gravity. Here, [Formula: see text] stands for the nonmetricity factor that drives gravitational interaction. We reconstructed the associated parameters with Tsallis holographic dark energy (THDE). We have solved the modified Einstein’s field equations by considering the bulk viscosity factor [Formula: see text]. Under the viscous and nonviscous THDE frameworks, we have obtained the expressions of [Formula: see text] using the power-law form of expansion. We have investigated the nature of various energy conditions for the stability analysis. The positive behavior of DEC and WEC indicates the model’s validation; on the other hand, SEC is violating, indicating the universe’s accelerated expansion. We have also investigated the reconstructed EoS parameter [Formula: see text] for bulk viscosity and obtained the one that lies in both quintessence and phantom regions. We also discussed the correspondence of the tachyon scalar field with THDE energy density in [Formula: see text] gravity. This correspondence permits the reconstruction of potentials and dynamics for scalar field models describing accelerated expansion.

Interacting Tsallis holographic dark energy and tachyon scalar field dark energy model in Bianchi type-II Universe

In this work, we study the interaction between the dark matter (DM) component and the dark energy (DE) component using the Tsallis holographic dark energy (THDE) density expression for a Bianchi type-II space–time within the framework of general relativity (GR). To obtain the exact solutions of Einstein’s field equations, we use two constraints: (i) the expansion scalar [Formula: see text] of the Universe is proportional to the component [Formula: see text] of the shear tensor [Formula: see text], i.e. [Formula: see text] and (ii) we assume that the scale factor follows the Hybrid Expansion Law (HEL). We have discussed some geometrical and physical parameters of our model such as the deceleration parameter (DP) and the equation of state (EoS) parameter. In these parameters, we plot their behavior in terms of redshift [Formula: see text]. We observe that the DP evolves from the early decelerating phase to the current accelerating phase with a current value consistent with the observation data. The EoS parameter evolves from a state of a stiff-matter fluid-dominated era [Formula: see text] for high redshift [Formula: see text] to a [Formula: see text]CDM era [Formula: see text] in the later times. Also, we have established a correspondence between the THDE model and the tachyon scalar field dark energy model. We have reconstructed the potential and the tachyon scalar field, which describes the current accelerated expansion of the Universe. Finally, using 51 values of observed Hubble measurement and the technique [Formula: see text]-test, we found the best fit value for the model parameters [Formula: see text], [Formula: see text] and [Formula: see text] (current value of the Hubble parameter). These results are consistent with the new measurements of [Formula: see text].37

A new class of holographic dark energy models in LRS Bianchi Type-I

In this paper, we examine the LRS Bianchi-type-I cosmological model with holographic dark energy. The exact solutions to the corresponding field equations are obtained by using the generalized hybrid expansion law (HEL). The EoS parameter [Formula: see text] for DE is found to be time-dependent and redshift-dependent and its exiting range for derived model is agreeing well with the current observations. Here, we likewise apply two mathematical diagnostics, the statefinders ([Formula: see text]) and [Formula: see text] plan to segregate HDE model from the [Formula: see text]CDM model. Here, the [Formula: see text] diagnostic trajectories are good tools to classify the dynamical DE model. We found that our model lies in both thawing region and freezing region. We also construct the potential as well as dynamics of the quintessence and tachyon scalar field. Some physical and geometric properties of this model along with the physical acceptability of cosmological solution have been discussed in detail.

Inflationary Dynamics of Tsallis Holographic Scalar Field Models in Chern-Simons Modified Gravity

The present study report reconstruction schemes for tachyon scalar field model of Dark Energy through Tsallis holographic dark fluid under the framework of Chern-Simons modified gravity. Emergent scale factor has been assumed. Reproducing the conservation equation for a coupled model with interaction term we have reconstructed the scalar field and the corresponding potential. The reconstructed energy density have been plotted for the case. Evolutionary behaviour of potential for the case have been pictorially presented.

Interacting tachyonic scalar field

We discuss the coupling between dark energy and matter by considering a homogeneous tachyonic scalar field as a candidate for dark energy. We obtained the functional form of scale factor by assuming that the coupling strength depends linearly on the Hubble parameter and energy density. We also estimated the cosmic age of the Universe for different values of coupling constant.

Evolution of matter perturbations and observational constraints on tachyon scalar field model

Abstract In this paper, the tachyon scalar field model is compared with the Λ C D M standard model using a set of observational data consisting of BBN, H(z), CMB, BAO, SNIa and f ( z ) σ 8 . The comparison is carried out at background and perturbation levels. Since the mass of the tachyon scalar field is very small and its effective sound speed is in the order of the speed of light ( c e f f ≈ 1 ) , the dark energy component remains homogeneous. The tachyon scalar field of dark energy model depends on its potential, therefore we consider the tachyon scalar field model based on a potential which is very popular in the literature, here in this work V ( ϕ ) = n 4 π G ( 1 − 2 3 n ) 1 ∕ 2 ( ϕ − ϕ 0 ) − 2 is chosen as the potential for the tachyon scalar field model. The evolution of equation of state parameter, density parameter, dimensionless Hubble parameter, deceleration parameter, the linear growth factor, the growth rate and f ( z ) σ 8 ( z ) for the tachyon scalar field model is compared with the Λ C D M , the holographic and the new agegraphic DE models. Although the tachyon scalar field model guarantees the acceleration of the universe’s expansion, the evolution of the deceleration parameter of the tachyon scalar field model enters to accelerating phase earlier than the other models. The growth rate of the cosmic structures, f ( z ) , is non-negligible at low redshifts for the tachyon scalar field model. In order to put constraints on the free parameters of the tachyon scalar field model, a standard Markov Chain Monte Carlo (MCMC) minimization method is utilized based on recent expansion and growth observational data. According to the values of the Akaike and Bayesian information criteria, we show that the tachyon scalar field model is inconsistent with the observational data and we can omit the tachyon scalar field model with the considered potential in this paper. Despite the considered potential is very popular in the literature, we should search for a better potential according to the available observational data.

Warm tachyon inflation and swampland criteria * * The work of A.M. has been supported financially by ‘Vice Chancellorship of Research and Technology, University of Kurdistan’ under research Project No.98/10/34704. The work of T. G. has been supported financially by ‘Vice Chancellorship of Research and Technology, University of Kurdistan’ under research Project No.98/11/2724

In this study, the scenario of a two-component warm tachyon inflation is considered, where the tachyon field plays the role of the inflaton by driving the inflation. During inflation, the tachyon scalar field interacts with the other component of the Universe, which is assumed to be photon gas, i.e., radiation. The interacting term contains a dissipation coefficient, and the study is modeled based on two different and familiar choices of the coefficient that were studied in the literature. By employing the latest observational data, the acceptable ranges for the free parameters of the model are obtained. For any choice within the estimated ranges, there is an acceptable concordance between the theoretical predictions and observations. Although the model is established based on several assumptions, it is crucial to verify their validity for the obtained values of the free parameters of the model. It is found that the model is not self-consistent for all values of the ranges, and for some cases, the assumptions are violated. Therefore, to achieve both self-consistency and agreement with the data, the parameters of the model must be constrained. Subsequently, we consider the recently proposed swampland conjecture, which imposes two conditions on the inflationary models. These criteria rule out some inflationary models; however, warm inflation is among those that successfully satisfy the swampland criteria. We conduct a precise investigation, which indicates that the proposed warm tachyon inflation cannot satisfy the swampland criteria for some cases. In fact, for the first case of the dissipation coefficient, in which, there is dependency only on the scalar field, the model agrees with observational data. However, it is in direct tension with the swampland criteria. Nevertheless, for the second case, wherein the dissipation coefficient has a dependency on both the scalar field and temperature, the model exhibits acceptable agreement with observational data, and suitably satisfies the swampland criteria.

Dynamical system analysis of Randall-Sundrum model with tachyon field on the brane

In this manuscript we use the dynamical system approach to study the linear dynamics of a Randall-Sundrum braneworld model with a tachyon scalar field confined to the brane. We recognize that the form of the tachyon potential plays a significant role in the evolution of the universe. For the case of an inverse square potential we find that one of our new variables, $\lambda$, is constant. We obtain critical points of the system in this situation and investigate their stability using the linear perturbation method. Then we turn to a Gaussian potential in which $\lambda$ is not constant. Using the idea of instantaneous critical points we study the behavior of the universe and its possible fates. One of the interesting results of this manuscript is that our universe will probably experience another phase transition from acceleration to deceleration in the future.

Perturbations in tachyon dark energy and their effect on matter clustering

A non-canonical scalar tachyon field is a viable candidate for dark energy and has been found to be in good agreement with observational data. Background data alone cannot completely rule out degeneracy between this model and others. To further constrain the parameters, apart from the distance measurements, we study perturbations in tachyon scalar field and how they affect matter clustering. We consider two tachyon potentials for this study, an inverse square potential and an exponential potential. We study the evolution of the gravitational potential, matter density contrast and dark energy density contrast, and compare them with the evolution in the ΛCDM model. Although perturbations in dark energy at sub-Hubble scales are negligible in comparison with matter perturbations, they cannot be ignored at Hubble and super-Hubble scales (λp > 1000 Mpc). We also study the evolution of growth function and growth rate of matter, and find that the growth rate is significantly suppressed in dark energy dominated era with respect to the growth rate for Λ CDM model. A comparison of these models with Redshift Space Distortion growth rate data is presented by way of calculating fσ8(z). There is a tension of 2.9σ (2.26σ) between growth rate data and Planck-2015 (Planck-2018) Cosmic Microwave Background Radiation data for Λ CDM model. We present constraints on free parameters of these models and show that perturbations in tachyon scalar field reduce this tension between different data sets.

Localization of Elko spinor fields in tachyonic de Sitter braneworld models

In this paper, we investigate the localization of a five-dimensional (5D) Elko spinor field in de Sitter tachyonic braneworld models. These branes are generated by gravity coupled to a tachyonic bulk scalar field and include a de Sitter cosmological background induced on the 3D-brane. Using Yukawa-type coupling mechanism we show that a free massless Elko spinor field cannot be localized on tachyonic de Sitter branes while massive Elko fields are localized if their bulk mass obeys an upper bound. Also by introducing a tachyonic function F(T) as Yukawa interaction term between the Elko spinor and the background tachyonic scalar field we find that localized massless zero modes are given in terms of general Heun functions. Furthermore, it is shown that employing a new derivative coupling term in the action of Elko spinor fields leads to the Elko field localization on tachyonic de Sitter branes.

A study of the bulk viscous pressure in scalar fields and holographic Ricci dark energy considered in the modified gravity framework

The work presented in this paper reports a rigorous study of the reconstruction of the modified gravity in the framework of the scalar field models of dark energy and holographic Ricci dark energy, a generalized version of the holographic dark energy presented in S. Nojiri and S.D. Odintsov. Gen. Relativ. Gravitation, 38, 1285 (2006). The tachyon and quintessence scalar fields have been considered and the cosmology associated with the presence of bulk viscosity has been studied. In the first part of our study, we have demonstrated the behaviour of the bulk viscosity coefficient in the framework of the reconstructed tachyon scalar field model of dark energy. The scale factor is chosen in the form a(t) = a0tβ, where β > 0. Two scalar field models, namely, tachyon and quintessence, have been considered in the framework of the modified field equations through incorporation of the bulk viscous pressure. The reconstructed density and pressure of the scalar field models have been explored for the cosmological consequences in the presence of bulk viscosity. The behaviour of the effective equation of state parameters has been investigated. Finally, we have reconstructed f(T) gravity in the presence of holographic Ricci dark energy and a transition of the effective equation of state parameter from quintessence to phantom has been observed.