Kourosh Nozari, Narges Rashidi
We study tachyon field inflation in the light of the Planck+WMAP+BICEP2+BAO joint data. While the minimally coupled tachyon field inflation is consistent with the Planck2013 data, it is not confirmed by the Planck+WMAP+BICEP2+BAO dataset. However, a nonminimally coupled tachyon field inflation is consistent with this joint dataset.
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For the constant-roll tachyon inflation, we derive the analytical expressions for the scalar and tensor power spectra, the scalar and tensor spectral tilts and the tensor to scalar ratio up to the first order by using the method of Bessel function approximation. The derived $n_s-r$ results for the constant-roll inflation are also compared with the observations, we find that only one constant-roll inflation is consistent with the observations and observations constrain the constant-roll inflation to be slow-roll inflation. The tachyon potential is also reconstructed for the constant-roll inflat…
An inflationary universe scenario in the context of tachyon field is studied. This study is done from an ansantz for the effective potential of cosmological perturbations $U(η)$. We describe in great detail the analytical solutions of the scalar and tensor perturbations for two different ansantz in the effective potential of cosmological perturbations; the Easther's model and an effective potential similar to power law inflation. Also we find from the background equations that the effective tachyonic potential $V(φ)$, in both models satisfy the properties of a tachyonic potential. We consider …
We study tachyon inflation within the large-$N$ formalism, which takes a prescription for the small Hubble flow slow--roll parameter $ε_1$ as a function of the large number of $e$-folds $N$. This leads to a classification of models through their behaviour at large $N$. In addition to the perturbative $N$ class, we introduce the polynomial and exponential classes for the $ε_1$ parameter. With this formalism we reconstruct a large number of potentials used previously in the literature for Tachyon Inflation. We also obtain new families of potentials form the polynomial class. We characterize the …
A model of tachyon inflation is proposed in the framework of holographic cosmology. The model is based on a holographic braneworld scenario with a D3-brane located at the holographic boundary of an asymptotic ADS$_5$ bulk. The tachyon field that drives inflation is represented by a DBI action on the brane. We solve the evolution equations analytically in the slow-roll regime and solve the exact equations numerically. We calculate the inflation parameters and compare the results with Planck 2018 data.
The tachyonic inflationary universe model in the context of intermediate inflation is studied. General conditions for this model to be realizable are discussed. In the slow-roll approximation, we describe in great details the characteristics of this model.
We study observational viability of Natural Inflation with a tachyon field as inflaton. By obtaining the main perturbation parameters in this model, we perform a numerical analysis on the parameter space of the model and in confrontation with $68\%$ and $95\%$ CL regions of Planck2015 data. By adopting a warped background geometry, we find some new constraints on the width of the potential in terms of its height and the warp factor. We show that the Tachyon Natural Inflation in the large width limit recovers the tachyon model with a $ϕ^{2}$ potential which is consistent with Planck2015 observa…
We obtain conditions for the existence of an attractor in the system of equations describing a tachyon warm inflationary model with bulk viscosity taken into account. When these conditions are met the evolution approaches slow-roll regime. We present the primordial power spectrum for the tachyon field by considering a dissipation coefficient depending on the scalar field and temperature.
Strongly non-geodesic, or rapidly turning trajectories in multifield inflation have attracted much interest recently from both theoretical and phenomenological perspectives. Most models with large turning rates in the literature are formulated as effective field theories. In this paper we investigate rapid-turn inflation in supergravity as a first step towards understanding them in string theory. We find that large turning rates can be generated in a wide class of models, at the cost of high field space curvature. In these models, while the inflationary trajectories are stable, one Hessian eig…
We derive a lower bound on the field excursion for the tachyon inflation, which is determined by the amplitude of the scalar perturbation and the number of $e$-folds before the end of inflation. Using the relation between the observables like $n_s$ and $r$ with the slow-roll parameters, we reconstruct three classes of tachyon potentials. The model parameters are determined from the observations before the potentials are reconstructed, and the observations prefer the concave potential. We also discuss the constraints from the reheating phase preceding the radiation domination for the three clas…
We study preheating in the Palatini formalism with a quadratic inflaton potential and an added $αR^2$ term. In such models, the oscillating inflaton field repeatedly returns to the plateau of the Einstein frame potential, on which the tachyonic instability fragments the inflaton condensate within less than an e-fold. We find that tachyonic preheating takes place when $α\gtrsim 10^{13}$ and that the energy density of the fragmented field grows with the rate $Γ/H \approx 0.011 \times α^{0.31}$. The model extends the family of plateau models with similar preheating behaviour. Although it contains…
In this paper we study a tachyon cosmological model based on dynamics of a 3-brane in the second Randall-Sundrum (RSII) model extended to include matter in the bulk. The presence of matter in the bulk changes warp factor which leads to modification of inflationary dynamics. The additional brane behaves effectively as a tachyon. We calculate numerically observation parameters of inflation: the scalar spectral index ($n_s$) and the tensor-to-scalar ratio ($r$) for the exponential potential of tachyon field.
Quantum Gravity Effects on the Tachyon Inflation from Thermodynamic Perspective
本研究在广义不确定原理下结合黑洞热力学熵-面积律导出的Friedmann方程，分析量子引力最小长度对快子暴胀的修正，通过多组观测数据验证，发现该修正可让原本不满足观测约束的快子暴胀模型具备观测合理性。
We investigate the feasibility of explosive particle production via parametric resonance or tachyonic preheating in multi-field inflationary models by means of lattice simulations. We observe a strong suppression of resonances in the presence of four-leg interactions between the inflaton fields and a scalar matter field, leading to insufficient preheating when more than two inflatons couple to the same matter field. This suppression is caused by a dephasing of the inflatons that increases the effective mass of the matter field. Including three-leg interactions leads to tachyonic preheating, wh…
The Standard Model Higgs becomes tachyonic at high energy scales according to current measurements. This unstable regime of the Higgs potential can be realized in the early Universe during high scale inflation, potentially with catastrophic consequences. This letter highlights a crucial inherent feature of such configurations that has so far remained ignored: Higgs particle production out of vacuum induced by the rapidly evolving Higgs field, which gets exponentially enhanced due to the tachyonic instability. Such explosive particle production can rapidly drain energy away from the Higgs field…
The emergent model in the context of loop quantum cosmology with a tachyon scalar field is studied. We find that there is a center equilibrium point in the semiclassical region and a saddle point in the classical region. If the potential of the tachyon field satisfies some conditions, the universe can stay at the center equilibrium point past-eternally and then oscillate infinitely around this point with the tachyon climbing up its potential. Once the potential reaches a critical value, these two equilibrium points coincide with each other and the oscillation phase is broken by an emergent inf…
$\mathcal{R}^2$-corrected Tachyon Scalar Field Inflation, the ACT Data, and Phantom Transition
本文研究了包含$\mathcal{R}^2$校正项的塔奇yon标量场膨胀模型，探讨其能否实现虚影分界线过渡，并与ACT数据相容。
We study the tachyon inflation in the presence of the superpotential as an inflationary potential. We study the primordial perturbations and their non-gaussian feature in the equilateral configuration. We use the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO joint data at $68\%$ CL and $95\%$ CL, to perform numerical analysis on the scalar perturbations and seek for the observational viability of the tachyon inflation with superpotential. We also check the observational viability of the model by studying the tensor part of the perturbations and comparing the results with Planck2018 TT, TE, EE+lo…
Tachyonic Encore: A universal shift of inflationary observables
提出一种与暴胀子势无关的机制，通过轻轴子旁观者场在暴胀后的超视界尺度上的瞬态快子相，增强曲率功率谱，压低张标比，并偏移标量谱指数，从而调和原本被排除的暴胀势与CMB观测。
The inflationary models developed in presence of a background radiation can be a solution to the reheating problem faced by common cold (isentropic) inflationary scenario. A D-brane system comprising of k Neuvo-Schwarz(NS) 5-branes with a transverse circle and BPS D3-branes with world volume parallel to the NS 5-branes, placed at a point on the transverse circle diametrically opposite to the NS 5-branes has a point of unstable equilibrium and the D3 brane has a geometric tachyonic mode associated with displacement of the brane along the circle. Cold inflationary scenario has been studied in co…
Tachyon inflation is one of the most attractive models of noncannonical inflation motivated by string theory. In this work we revisit the constraints on tachyon inflation with inverse $\cosh$ potential and exponential potential considering reheating, Although the phase of reheating is not well understood, it can be parameterized in terms of reheating temperature $T_{re}$, number of e-folds during reheating $N_{re}$ and effective equation of state during reheating $w_{re}$, which can be related to the parameters of the tachyon potential, spectral index $n_s$ and tensor-to-scalar ratio $r$. For …
In order to study the effect of the anti de Sitter/ conformal field theory correspondence (AdS/CFT) on the primordial inflationary era, we consider a universe filled with a tachyon field in a slow-roll regime. In this context, the background and perturbative parameters characterising the inflationary era are related to the standard one by correction terms. We show a clear agreement between the theoretical prediction and the observational data for the above mentioned model. The main results of our work are illustrated for an exponential potential. We show that, for a suitable conformal anomaly …
Tachyonic gravitational dark matter production after inflation
本文提出一种通过曲率诱导的超光速不稳定性在暴胀后非热产生暗物质的引力机制，通过实数观察者标量场与时空曲率不变量的二次耦合，计算暗物质丰度并提供简单拟合函数。
In this article, our prime objective is to study the inflationary paradigm from generalized tachyon (GTachyon) living on the world volume of a non-BPS string theory. The tachyon action is considered here is getting modified compared to the original action. One can quantify the amount of the modification via a power $q$ instead of $1/2$ in the effective action. Using this set up we study inflation from various types of tachyonic potentials, using which we constrain the index $q$ within, $1/2<q<2$, Regge slope $α^{'}$, string coupling constant $g_{s}$ and mass scale of tachyon $M_s$, from the re…
We constrain several models in Tachyonic Inflation derived from the large-$N$ formalism by considering theoretical aspects as well as the latest observational data. On the theoretical side, we assess the field range of our models by means of the excursion of the equivalent canonical field. On the observational side, we employ BK14+PLANCK+BAO data to perform a parameter estimation analysis as well as a Bayesian model selection to distinguish the most favoured models among all four classes here presented. We observe that the original potential $V \propto \textrm{sech}(T)$ is strongly disfavoured…
Viable Anisotropic Inflation and Reheating in the Tachyon Model
该研究针对各向异性背景下的中间快子暴胀展开，推导慢滚参数并结合多组观测数据验证其观测可行性，同时分析了非高斯性振幅与再加热过程的相关特性。
We present a systematic method for evaluation of perturbation observables in non-canonical single-field inflation models within the slow-roll approximation, which allied with field redefinitions enables predictions to be established for a wide range of models. We use this to investigate various non-canonical inflation models, including Tachyon inflation and DBI inflation. The Lambert $W$ function will be used extensively in our method for the evaluation of observables. In the Tachyon case, in the slow-roll approximation the model can be approximated by a canonical field with a redefined potent…
With the help of the tachyonic trapping mechanism one can potentially solve a number of problems affecting quintessential inflation models. In this mechanism we introduce a trapping field with a spontaneous symmetry breaking potential. When the quintessential inflaton passes the critical point, a sudden burst of particle production is able to reheat the Universe and trap the inflaton away from theminimum of its potential. However, self-interactions of the trapping field suppress particle production and reduce the efficiency of this process. We develop a method to compute the magnitude of the s…
We show that a dark Higgs field charged under U(1)$_{\rm H}$ gauge symmetry is trapped at the origin for a long time, if dark photons are produced by an axion condensate via tachyonic preheating. The trapped dark Higgs can drive late-time inflation, producing a large amount of entropy. Unlike thermal inflation, the dark Higgs potential does not have to be very flat, because the effective mass for the dark Higgs is enhanced by large field values of dark photons with extremely low momentum. After inflation, the dark Higgs decays into massive dark photons, which further decay into the SM particle…
We consider the mimetic tachyon model in the Lagrange multiplier approach. We study both the linear and non-linear perturbations and find the perturbation and non-gaussianity parameters in this setup. By adopting two types of the scale factor as the power-law ($a=a_{0}\,t^{n}$) and intermediate ($a=a_{0}\exp(bt^β)$) scale factors, we perform a numerical analysis on the model which is based on Planck2018 TT, TE, EE+lowE+lensing +BAO +BK14 and Planck2018 TTT, EEE, TTE and EET data sets. We show that the mimetic tachyon model with both the power-law and intermediate scale factors, in some ranges …
By using the formulation of the reconstruction, we explicitly construct models of $k$-essence, which unify the inflation in the early universe and the late accelerating expansion of the present universe by a single scalar field. Due to the higher derivative terms, the solution describing the unification can be stable in the space of solutions, which makes the restriction for the initial condition relaxed. The higher derivative terms also eliminate tachyon. Therefore we can construct a model describing the time development, which cannot be realized by a usual inflaton or quintessence models of …
By adopting the intermediate and power-law scale factors, we study the tachyon inflation with constant sound speed. We perform some numerical analysis on the perturbation and non-gaussianity parameters in this model and compare the results with observational data. By using the constraints on the scalar spectral index and tensor-to-scalar-ratio, obtained from Planck2018 TT, TE, EE+lowE+lensing+BAO+BK14 data, the constraint on the running of the scalar spectral index obtained from Planck2018 TT, TE, EE+lowEB+lensing data, and constraint on tensor spectral index obtained from Planck2018 TT, TE, E…
We revisit the mechanism of helical magnetogenesis during inflation with a parity violating interaction using the formalism of stochastic inflation. One of the polarization of the gauge field undergoes tachyonic growth leading to the generation of helical magnetic fields. We obtain the Langevin equations associated with the electromagnetic fields which are in the form of Ornstein-Uhlenbeck stochastic differential equations. Consequently, the tachyonic growth of the helical magnetic fields is balanced by a mean-reverting process of stochastic dynamics such that the magnetic fields settle down t…
A Cosmological Tachyon Collider: Enhancing the Long-Short Scale Coupling
本文提出将瞬态快子标量场一致嵌入暴胀的模型，利用红外有限耦合产生压缩极限下增强的长短尺度交换三点谱，并指出CMB-S4等实验可通过谱畸变约束其参数空间。
We study a model of quintessential inflation in the context of Palatini gravity. As a representative example, we consider the Peebles-Vilenkin model of quintessential inflation with a small non-minimal coupling to gravity, which is consistent with the most recent Planck measurements. At the end of inflation, the inflaton field passes through a tachyonic region and it leads to explosive particle production through the tachyonic preheating process. After preheating, the Universe becomes dominated by the kinetic energy of the inflaton and enters a period of kination. Eventually, the total energy …
We analyze the dynamics and observational predictions of supersymmetric hybrid inflation in the warm regime, where dissipative effects are mediated by the waterfall fields and their subsequent decay into light degrees of freedom. This produces a quasi-thermal radiation bath with a slowly-varying temperature during inflation and further damps the inflaton's motion, thus prolonging inflation. As in the standard supercooled scenario, inflation ends when the waterfall fields become tachyonic and can no longer sustain a nearly constant vacuum energy, but the interaction with the radiation bath make…
Hybrid inflation and gravitational waves from accidentally light scalars
本文构建了一个由辐射修正产生暴胀子势的混合暴胀模型，通过快子瀑布场结束暴胀，并预测了其产生的引力波可被未来实验或脉冲星计时阵列探测到。
We study preheating after hilltop inflation where the inflaton couples to another scalar field, e.g. a right-handed sneutrino, which provides a mechanism for generating the correct initial conditions for inflation and also a decay channel for the inflaton that allows for reheating and non-thermal leptogenesis. In the presence of such a coupling, we find that after the phases of tachyonic preheating and tachyonic oscillations, during which the inflaton field becomes inhomogeneous, there can be a subsequent preheating phase where the fluctuations of the other field get resonantly enhanced, from …
Reheating after Axion Inflation
研究轴子暴胀模型中暴胀子通过Chern-Simons耦合与非阿贝尔规范场作用的再加热过程，发现并非如预期般立即完成，而是由暴胀子凝聚体、粒子或胶球主导宇宙后经微扰衰变完成。
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