arXiv subjects

Maryam Roushan

Publications and source records attributed to Maryam Roushan.

7 recordsLinked to original sources

arXiv2026

Anisotropic Dirac-Born-Infeld Inflation with Non-Vacuum Initial States: Primordial Perturbations, Non-Gaussianity, and Observational Constraints

We investigate linear and nonlinear primordial perturbations in an anisotropic Dirac-Born-Infeld (DBI) inflationary model with a non-vacuum initial state. Using the Arnowitt-Deser- Misner (ADM) formalism, we expand the action up to second and third order in the curvature perturbation and derive the corresponding scalar and tensor power spectra, as well as the bispectrum and the equilateral non-linearity parameter $f_{NL}^{\mathrm{equil}}$. The effects of anisotropic corrections and non-Bunch-Davies (non-BD) initial conditions are incorporated through the slow-roll sector and Bogoliubov coefficients. For the numerical analysis, we consider an intermediate expansion scenario together with a phenomenological ansatz for the excited-state occupation number $N_k$. By comparing the model predictions with recent observational datasets, including Planck2018 TT, TE, EE + lowE + lensing + BK18 + BAO and DESI+CMB+DESY5 data, we identify observationally viable regions in the parameter space of the model. Our analysis indicates that the anisotropic DBI scenario with non-vacuum initial conditions can remain compatible with current constraints on the scalar spectral index, tensor-to-scalar ratio, and equilateral non-Gaussianity for suitable ranges of the anisotropy parameter $c$ and the initial-state parameter $N_{k,0}$.

astro-ph.CO↗

arXiv2026

Observational Viability of $\phi^{2}$-Superpotential Inflation with GUP-Induced Corrections

We study a $\phi^{2}$-superpotential inflationary model within a GUP-inspired quantum-gravity framework. Using horizon thermodynamics, we review the GUP-corrected Friedmann equations obtained by combining the temperature--surface-gravity relation with a modified entropy--area law. Reformulating the dynamics via a superpotential $W(\phi)$ with $\phi=\phi(a)$, we obtain the corresponding slow-roll parameters and derive GUP-modified expressions for the scalar spectral index and the tensor-to-scalar ratio, leading to a deformation of the standard inflationary consistency relation. Adopting the quadratic ansatz $W(\phi)=\tfrac{1}{2}m^{2}\phi^{2}$, we evaluate the observables $(n_{s},r)$ and compare them with the Planck 2018 TT, TE, EE + lowE + lensing + BK18 + BAO, DESI + CMB + DESY5, and Planck2018 + ACT + lensing + BK18 + BAO (from DESI) datasets. The analysis shows that, for moderately negative values of the effective GUP parameter $\beta$ and sub-unity values of the phenomenological superpotential parameter $C$, the model predictions can fall within the $68\%$ and $95\%$ confidence regions of current observations. These results indicate that GUP-inspired corrections can shift the $(n_{s},r)$ predictions of a quadratic superpotential toward the observationally favored region.

physics.gen-ph↗

arXiv2025

Cosmological Implications of the Extended Uncertainty Principle: Energy Conditions, Stability, and Late Time Acceleration

We study the cosmological consequences of the Extended Uncertainty Principle (EUP) by deriving modified Friedmann equations through thermodynamic arguments. The evolution of the effective equation of state induced by EUP corrections is analyzed and characterized using the Chevallier-Polarski-Linder (CPL) parametrization. We then examine the fulfillment of classical energy conditions, including the null, weak, strong, and dominant conditions. The dynamical and thermodynamic stability of the model is investigated, showing that the EUP cosmology admits a late-time de Sitter attractor. Finally, we evaluate the effective speed of sound associated with the model and discuss implications for perturbative stability. Our findings indicate that EUP-induced corrections can produce a consistent late-time acceleration without requiring a cosmological constant.

gr-qc↗

arXiv2025

Observational Viability of Anisotropic Inflation Revisited

We investigate anisotropic inflation within the single-field model featuring an intermediate scale factor. Our analysis reveals that the anisotropic nature of the Friedmann equations in this framework affects the slow-roll parameters, which in turn influence key perturbation parameters. Using a numerical approach, we derive constraints on the intermediate parameter $β$ and the anisotropic parameter $c$. Our results show that the model is consistent with Planck2018 TT, TE, EE +lowE+lensing+BK14+BAO data at $68\%$ CL, for $0.84<β<1$ and $7.34<c<27.7$. At $95\%$ CL the consistency holds for $0.77<β<1$ and $7.17<c<28.9$. The model is also consistent with Planck2018 TT, TE, EE +lowE+lensing+BK18+BAO data, for $0.91<β<1$ and $8.00<c<27.4$ (at $68\%$ CL), and $0.88<β<1$ and $7.40<c<28.8$ (at $95\%$ CL). Additionally, we examine the reheating phase using these constraints on constraints on $β$ and $c$ and determine the observationally consistent ranges for the number of e-folds and the temperature during the reheating phase.

astro-ph.CO↗

arXiv2024

Traces of Quantum Gravity Effects at Late time Cosmological Dynamics via Distance Measures

Inspired by the entropy-area relation of black hole thermodynamics, we study the thermodynamics of cosmological apparent horizon in a spatially flat Friedmann-Robertson-Walker (FRW) universe in the framework of an Extended Uncertainty Principle (EUP). The adopted EUP naturally admits a minimal measurable momentum (equivalently a maximal measurable length), as an infrared cutoff in the theory. We derive the modified Friedmann equations in this setup and explore some predictions of these equations for the late time universe via distance measures. We show that in this framework it is possible to realize the late time cosmic speed-up and transition to the phantom phase of the equation of state parameter of the effective cosmic fluid without recourse to any dark energy component or modified gravity. Inspection of various distance measures in this framework shows that an EUP with a negative deformation parameter suffices for the interpretation of the late time asymptotically de Sitter universe with standard non-relativistic matter.

gr-qc↗

arXiv2024

Observational Viability of the Intermediate DBI Inflation in the Presence of a Minimal Length

We consider an intermediate Dirac-Born-Infeld (DBI) inflationary model in the presence of a minimal measurable length in the theory. We show that, the presence of a minimal measurable length modifies the definitions of the scalar and tensor spectral indices and also other inflation observables. This is due to modification of the momentum and corresponding wave number of the perturbations in the presence of a minimal length. By using the deformed definition of the scalar and tensor spectral indices, we perform numerical analysis on the intermediate DBI inflation model to find some constraints on the deformation parameter. In this regard, we compare our numerical results with both Planck2018 TT, TE, EE +lowE +lensing +BAO+ BK14 and Planck2018 TT, TE,EE +lowE+lensing+BK14 +BAO+LIGO $\&$ Virgo2016 data at the $68\%$ CL and $95\%$ CL. Our numerical study shows that the intermediate DBI inflation model in the presence of a minimal measurable length is observationally viable if the upper bound on the deformation parameter to be considered of the order of $10^{48}$ at $68\%$ CL and $10^{49}$ at $95\%$ CL. This is consistent with the results of other approaches to constrain such a quantity.

astro-ph.CO↗

arXiv2022

Visible Energy Alternative to Dark Energy

Quantum gravitational effects usually are assumed to be important on small scale (Planck scale), but actually these effects are also very significant on large (cosmological) scales. It is recognized that in curved spacetime, the existence of a minimal measurable momentum is inevitable. In this paper, we study thermodynamic properties of the late time universe in the presence of a minimal measurable momentum cutoff that encodes infra-red modification of the underlying field theory. In this regard, we consider a non-relativistic regime and show that the existence of a minimal measurable momentum in the very essence of the theory leads to accelerating expansion of the universe, which can be interpreted as an alternative to Dark Energy. The universe in this model has experienced the phantom line crossing in the near past.

gr-qc↗