arXiv subjects

Maryam Aghaei Abchouyeh

Publications and source records attributed to Maryam Aghaei Abchouyeh.

8 recordsLinked to original sources

arXiv2026

Efficient searches of small signals across two-channel noisy data: a challenge in Big Data observations

Searching for novel small signals in noisy data is preferably pursued by correlation in two or more independently operating channels. Signals of potential interest exist in tails beyond $κσ$, where $κ$ denotes a multiple of the standard deviation $σ$ of the data. Since moving data is a major cost factor in Big Data analysis and heterogeneous computing more generally, efficiency may be optimized by restricting the correlations computation to the tails of two-channel data exceeding $κσ$. Already, a moderate value $κ\gtrsim2$ realizes a data-reduction by at least an order of magnitude. Here, we study this approach using a novel {\it Excess Probability Ratio} (EPR), correlating Boolean data resulting from tails beyond a cut-off $κσ$. We compare and rank EPR performance against conventional direct cross-correlation (DCC) and Pearson coefficient (PC), applicable to the original data with no cut-off. This benchmark is performed over different combinations of background noise Gaussian, Poisson and Uniform and signals Gaussian, Poisson, Uniform, Chirps and Sine waves. Results show performance of EPR to be comparable to that of PC, providing a new approach for significant improvements in efficiency with essentially no loss of sensitivity, relevant to the present era of Big Data observatories.

astro-ph.IM↗

arXiv2026

Is Dark Energy Increasing or Decreasing in the Late Universe?

The concordance cosmological model $Λ$CDM assumes dark energy to be a constant, consistent with early-time observations, evidenced by Planck-$Λ$CDM analyses. However, in the face of late-time tensions, the nature of dark energy remains a central open problem. Modern precision cosmology offers a potential new window in the $w(a){\rm CDM}$ framework, which provides a model-independent prescription for its unknown equation of state $w(a)$. A confrontation of $w(a){\rm CDM}$ with data generally constitutes a nonlinear inference problem. We find that $w_0w_a$ estimates posterior to a fully non-linear $w(a)$ analysis are stabilized by the {\it Baryon Acoustic Oscillation} (BAO) constraint on $c_M=Ω_{m,0}h^2$, inherited for instance from Planck-$Λ$CDM analysis of the CMB. It produces $w_0w_a$ estimates that are invariant under constraint-preserving variations in $Ω_{m,0}$. In contrast, the early-linearization $w_0w_a$CDM shows pronounced correlation with $Ω_{m,0}$ even when preserving $c_M$. We quantify this correlation resulting from the non-commutativity of $w_0w_a$ estimation and linearization in $w(a)$CDM. This discrepancy is demonstrated in controlled mock-data experiments. Applied to cosmic chronometer data, $w_0w_a$ estimates from correlation-free late linearization of $w(a)$CDM analysis favor $w_0<-1$, whereas $w_0w_a$CDM favors $w_0>-1$. If the correlation between $w_0$ and $Ω_{m,0}$ in $w_0w_a$CDM is interpreted as arising from linearization effects rather than a physical origin, application to DESI DR2 may shift $w_0$ downward, potentially extending to $w_0 < -1$, corresponding to increasing dark energy at the present epoch. Alternatively, if the correlation is of hitherto unseen physical origin, the $w_0w_a$CDM parametrization is self-consistent and no such correction to the DESI inference may be required.

astro-ph.CO↗

arXiv2026

Multimessenger Constraints on the Central Engine in SN 2023ixf: Neutron Star or Black Hole?

The physical trigger of core-collapse supernova (CC-SNe) is a central theme in modern surveys of the transient Universe. A multi-messenger approach may provide a unique window to CC-SNe produced by a newly born neutron star (NS) or black hole (BH). Here we apply joint electromagnetic-gravitational wave (EM-GW) analysis to the nearby event SN 2023ixf using a model-independent broadband search with a GW-energy detection threshold of a few times $10^{-5} M_\odot c^2$ for chirps and $10^{-2}$ $M_\odot c^2$ for noise-like emission below 1\,kHz. No joint LIGO Hanford-Livingston (H1-L1) signal associated with SN 2023ixf is observed over a 2.5 day window proceeding the first discovery. Together with EM photometric-spectroscopic data, we interpret this null result to indicate the absence of BH formation, in part by mass-scaling of the BH powering GW170817B following GW170817. This multi-messenger outcome supports, hereby, scenarios consistent with NS formation, consistent with a progenitor mass likely below $\sim 20 M_\odot$ estimated by EM interpretations.

astro-ph.HE↗

arXiv2023

A bound on the cosmic opacity of unparticles from the CMB temperature

Unparticle cosmology gives an unconventional outlook on the dark sector of cosmology, increasingly challenging $Λ\mbox{CDM}$ by $H_0$-tension. This model derives from a finite temperature broken conformal symmetry of radiation, described by a non-radiative correction with unknown sign in energy density. This symmetry breaking has a sign ambiguity, in which corrections about the IR fixed point are normal or tachyonic. While the first has been ruled out in a recent study, the latter possesses a late-time temperature $T_c\simeq 4\,T_{CMB}$ associated with $Ω_{\cal U}\simeq 1$ ($Ω_{\cal U} \simeq 10^4 Ω_{CMB}$), where $T_{CMB}$ denotes the temperature of the Cosmic Microwave Background (CMB). Thus exposed to the enormous heat bath of unparticles, $T_{CMB}$ is constrained by the astronomical age of the Universe $T_{u,0}$. The relative temperature shift $ΔT/T$ in any heat exchange to the CMB is hereby limited to the uncertainty of a few percent in $T_{u,0}$. This bounds the effective cross-section of unparticles interactions with CMB photons to $σ_{γ\mathcal{U}} \lesssim 10^{-40}\ \mbox{m}^2=10^{-3}\ \mbox{nb}$. Assuming a standard cross-section across the broadband mass and energy spectrum of unparticles, a more stringent bound $σ_{γ\mathcal{U}} \lesssim 10^{-3}\,\mbox{pb}$ derives from COBE-FIRAS constraints on spectral distortions. The first is midway of photon-neutrino $σ_{γν}$ and photon-photon cross sections $σ_{γγ}$, the second is on par with $σ_{γν}$. These constraints put late-time unparticle cosmology, if present, at the edge of the standard model.

astro-ph.CO↗

arXiv2020

Late time dynamics of $f(R, T, R_{μν}T^{μν})$ gravity

Dynamical behavior and future singularities of $f(R, T,R_{μν}T^{μν})$ gravitational theory are investigated. This gravitational model is a more complete form of the $f(R,T)$ gravity which can offer new dynamics for the universe. We investigate this gravitational theory for the case $f = R + αR_{μν}T^{μν}$ using the method of autonomous dynamical systems and by assuming an interaction between matter and dark energy. The fixed points are identified and the results are consistent with standard cosmology and show that for small $α$, the radiation dominated era is an unstable fixed point of the theory and the universe will continue its procedure toward matter era which is a saddle point of the theory and allows the evolution to dark energy dominated universe. Finally the dark energy dominated epoch is a stable fixed point and will be the late time attractor for the universe. We also consider future singularities for the two $f = R + αR_{μν}T^{μν}$ and $f = R +αRR_{μν}T^{μν}$ cases and for $w = 0,\dfrac{1}{3},1$ and $-1$. Our results show that for the case of $f = R + αR_{μν}T^{μν}$, the future singularities of the universe will happen in the same condition as do for the Einstein-Hilbert FRW universe. However, a new type of singularity is obtained for $f = R +αRR_{μν}T^{μν}$ that is captured by $t\rightarrow t_s;\ a \rightarrow a_s;\ ρ\rightarrow \infty;$ and $\ |p| \rightarrow 0$.

gr-qc↗

arXiv2020

Dynamical behavior of the Universe: an entropic force scenario

Entropic force originates in the assumption that there is a horizon for the universe. This horizon gives rise to additional terms in the equations of motion. Using dynamical system calculations, our results show that in the presence of dark energy for certain conditions, the last attractor of this theory will be dark energy epoch, but in the absence of dark energy, entropic force energy portion will have the lead role in the late time universe and is responsible for accelerated expansion of that. Interestingly, assuming both entropic force terms and dark energy to have their share of energy density of the universe, we have found that, in certain conditions entropic force dominated epoch is a stable fixed point while the dark energy epoch is a saddle point.

gr-qc↗

arXiv2018

Anyon Black Holes

We propose a correspondence between an Anyon Van der Waals fluid and a (2+1) dimensional AdS black hole. Anyons are particles with intermediate statistics that interpolates between a Fermi-Dirac statistics and a Bose-Einstein one. A parameter $α$ ($0<α<1$) characterizes this intermediate statistics of Anyons. The equation of state for the Anyon Van der Waals fluid shows that it has a quasi Fermi-Dirac statistics for $α> α_c$, but a quasi Bose-Einstein statistics for $α< α_c$. By defining a general form of the metric for the (2+1) dimensional AdS black hole and considering the temperature of the black hole to be equal with that of the Anyon Van der Waals fluid, we construct the exact form of the metric for a (2+1) dimensional AdS black hole. The thermodynamic properties of this black hole is consistent with those of the Anyon Van der Waals fluid. For $α< α_c$, the solution exhibits a quasi Bose-Einstein statistics. For $α> α_c$ and a range of values of the cosmological constant, there is, however, no event horizon so there is no black hole solution. Thus, for these values of cosmological constants, the AdS Anyon Van der Waals black holes have only quasi Bose-Einstein statistics.

hep-th↗

arXiv2014

Entropic force, running gravitational coupling and future singularities

The effects of a running gravitational coupling and the entropic force on future singularities are considered. Although it is expected that the quantum corrections remove the future singularities or change the singularity type, treating the running gravitational coupling as a function of energy density is found to cause no change in the type of singularity but causes a delay in the time that a singularity occurs. The entropic force is found to replaces the singularity type $II$ by $\bar{III}$ ($a=$const., $H=$const., $\dot{H} \to \infty$, $p \to \infty$, $ρ\to \infty$) which differs from previously known type $III$ and to remove the $w$-singularity. We also consider an effective cosmological model and show that the types $I$ and $II$ are replaced by the singularity type $III$.

gr-qc↗