arXiv subjects

Amin Aboubrahim

Publications and source records attributed to Amin Aboubrahim.

At least 19 recordsLinked to original sources

arXiv2026

Automatic detection of fast oscillations of dark matter scalar field and updated cosmological constraints on QCDM

It is well known that a scalar field dark matter with a quadratic potential undergoes fast oscillations when the time period represented by the mass scale in the Klein-Gordon equation becomes much smaller than that set by the Hubble parameter. This makes a solution to the equation numerically intractable. Many works in the literature have addressed the problem by either switching between solving the Klein-Gordon equation in the well-behaved regime to solving the fluid equations at the onset of oscillations, or by introducing a new set of variables that can absorb these oscillations. Despite being successful, these techniques rely on an estimate of when the oscillations start. For large scale scans of a model's parameter space, this can become cumbersome. Furthermore, the techniques have been used mainly for non-interacting dark matter models. In this work, we introduce an averaging technique with an automatic detection of the onset of oscillations, capable of capturing the non-interacting as well as the interacting dark matter scenarios. The technique, implemented in \texttt{CLASS}, is tested on the QCDM model and shows excellent detection and averaging abilities. We also update the cosmological constraints on the model using the most recent public data.

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arXiv2026

A study of dark matter-dark energy interaction under the DESI DR2 data constraint

While $\Lambda$CDM provides a good fit to cosmological data, it fails to address many of the outstanding questions in contemporary cosmology. Chief among these are the Hubble tension and the apparent dynamical nature of dark energy as inferred from the recent DESI DR2 analysis. In this work, we analyze a field-theoretic description of cosmology where both dark energy and dark matter are interacting spin zero fields. We give a thorough study of a wide range of the interaction strength and demonstrate the effect on the dark energy equation of state and the Hubble tension. Using the recent cosmological data, we extract constraints on cosmological parameters including the free parameters of the model.

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arXiv2025

Cosmology of axion dark energy in supersymmetric models and constraints on high scale parameters

An analysis is given of interacting dark energy and dark matter where the dark energy is assumed to be an ultralight axionic field with a pseudo-Nambu-Goldstone Boson potential which is in general a superposition of $N$ number of cosine terms motivated by supergravity and string models with a $U(1)$ global symmetry, where the symmetry is broken by instanton effects. The case $N=2$ is investigated in detail and a fit to cosmological data is performed where it is found that a better fit is obtained in comparison with the $N=1$ case. The fits also constrain high scale parameters, i.e., the axion decay constant which is determined to be sub-Planckian, a result consistent with string theory that disfavors trans-Planckian axion decay constant. Furthermore, the dark energy-dark matter interaction strength is constrained to be feeble, i.e., $\lambda\lesssim 4\times 10^{-6}$ m$_{\rm Pl}^{-2}$ Mpc$^{-2}$. We study possible implications of this type of potential on the Hubble tension and on the dynamics of the dark energy equation of state using the DESI-DR2 data. For the cases $N=3,4$, the analysis exhibits the phenomenon of transmutation even in the absence of coupling to dark matter, where thawing quintessence transmutes to freezing quintessence. The analysis is internally consistent in its treatment of the dark energy-dark matter interaction as it is based on an underlying Lagrangian, in contrast with several previous works where the sources are chosen in an ad hoc manner to satisfy energy conservation.

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arXiv2025

The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. [Abridged]

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arXiv2025

Cosmological tensions and $\mathcal{Q}_{\rm CDM}$ as an alternative to $\Lambda$CDM

The Standard Model of cosmology, $\Lambda$CDM, while enormously successful, is currently unable to account for several cosmological anomalies the most prominent of which are in the measurements of the Hubble parameter and $S_8$. Additionally, the inclusion of the cosmological constant is theoretically unappealing. This has lead to extensions of the model such as the use of fluid equations for interacting dark matter and dark energy which, however, are ad hoc since they do not appear to arise from a Lagrangian. Recently, we have proposed $\mathcal{Q}_{\rm CDM}$ as an alternative to $\Lambda$CDM which is a dynamical model of a quintessence field interacting with dark matter within a field theoretic approach. In this approach, we analyze the effect of the dark matter mass, the dark matter-dark energy interaction strength and the dark matter self-interaction on the cosmological parameters. Further, within $\mathcal{Q}_{\rm CDM}$ we investigate the possible alleviation of the Hubble tension and the $S_8$ anomaly and the nature of dark energy.

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arXiv2024

Upper limits on dark energy-dark matter interaction from DESI DR2 in a field-theoretic analysis

One of the important issues both in particle physics and cosmology relates to whether dark energy is a cosmological constant $\Lambda$, or is dynamical in nature such as quintessence. In this work, we discuss a model of quintessence interacting with dark matter and analyze the resulting phenomenology of the dark energy equation of state. We identify two regions where the equation of state behaves differently depending on the size of the dark matter-dark energy interaction strength. We show that the strong coupling region induces a transmutation of quintessence from thawing to freezing. Using the recent data release from the Dark Energy Spectroscopic Instrument (DESI), we rule out this possibility of transmutation and investigate the weak coupling region to derive upper limits on the interaction strength. Our analysis indicates that while $\Lambda$CDM lies within the $1\sigma$ contour in the $w_0$-$w_a$ plane, the best fit points lie in the fourth quadrant and show deviations from the $\Lambda$CDM prediction.

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arXiv2024

Interacting ultralight dark matter and dark energy and fits to cosmological data in a field theory approach

The description of dark matter as a pressure-less fluid and of dark energy as a cosmological constant, both minimally coupled to gravity, constitutes the basis of the concordance $\Lambda\text{CDM}$ model. However, the concordance model is based on using equations of motion directly for the fluids with constraints placed on their sources, and lacks an underlying Lagrangian. In this work, we propose a Lagrangian model of two spin zero fields describing dark energy and dark matter with an interaction term between the two along with self-interactions. We study the background evolution of the fields as well as their linear perturbations, suggesting an alternative to $\Lambda$CDM with dark matter and dark energy being fundamental dynamical fields. The parameters of the model are extracted using a Bayesian inference tool based on multiple cosmological data sets which include those of Planck (with lensing), BAO, Pantheon, SH0ES, and WiggleZ. Using these data, we set constraints on the dark matter mass and the interaction strengths. Furthermore, we find that the model is able to alleviate the Hubble tension for some data sets while also resolving the $S_8$ tension.

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arXiv2023

Forbidden dark matter annihilation into leptons with full collision terms

The standard approach of calculating the relic density of thermally produced dark matter based on the assumption of kinetic equilibrium is known to fail for forbidden dark matter models since only the high momentum tail of the dark matter phase space distribution function contributes significantly to dark matter annihilations. Furthermore, it is known that the computationally less expensive Fokker-Planck approximation for the collision term describing elastic scattering processes between non-relativistic dark matter particles and the Standard Model thermal bath breaks down if both scattering partners are close in mass. This, however, is the defining feature of the forbidden dark matter paradigm. In this paper, we therefore include the full elastic collision term in the full momentum-dependent Boltzmann equation as well as in a set of fluid equations that couple the evolution of the number density and dark matter temperature for a simplified model featuring forbidden dark matter annihilations into muon or tau leptons through a scalar mediator. On the technical side, we perform all angular integrals in the full collision term analytically and take into account the effect of dark matter self-interactions on the relic density. The overall phenomenological outcome is that the updated relic density calculation results in a significant reduction of the experimentally allowed parameter space compared to the traditional approach, which solves only for the abundance. In addition, almost the entire currently viable parameter space can be probed with CMB-S4, next-generation beam-dump experiments or at a future high-luminosity electron-position collider, except for the resonant region where the mediator corresponds to approximately twice the muon or tau mass.

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arXiv2023

Combined constraints on dark photons and discovery prospects at the LHC and the Forward Physics Facility

Hidden sectors are ubiquitous in supergravity theories, in strings and in branes. Well motivated models such as the Stueckelberg hidden sector model could provide a candidate for dark matter. In such models, the hidden sector communicates with the visible sector via the exchange of a dark photon (dark $Z'$) while dark matter is constituted of Dirac fermions in the hidden sector. Using data from collider searches and precision measurements of SM processes as well as the most recent limits from dark matter direct and indirect detection experiments, we perform a comprehensive scan over a wide range of the $Z'$ mass and set exclusion bounds on the parameter space from sub-GeV to several TeV. We then discuss the discovery potential of an $\mathcal{O}$(TeV) scale $Z'$ at HL-LHC and the ability of future forward detectors to probe very weakly interacting sub-GeV $Z'$ bosons. Our analysis shows that the parameter space in which a $Z'$ can decay to hidden sector dark matter is severely constrained whereas limits become much weaker for a $Z'$ with no dark decays. The analysis also favors a self-thermalized dark sector which is necessary to satisfy the dark matter relic density.

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arXiv2022

Report of the Topical Group on Physics Beyond the Standard Model at Energy Frontier for Snowmass 2021

This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection.

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arXiv2022

TF08 Snowmass Report: BSM Model Building

We summarize the state of Beyond the Standard Model (BSM) model building in particle physics for Snowmass 2021, focusing mainly on several whitepaper contributions to BSM model building (TF08) and closely related areas.

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arXiv2022

Report of the Topical Group on Cosmic Probes of Fundamental Physics for for Snowmass 2021

Cosmic Probes of Fundamental Physics take two primary forms: Very high energy particles (cosmic rays, neutrinos, and gamma rays) and gravitational waves. Already today, these probes give access to fundamental physics not available by any other means, helping elucidate the underlying theory that completes the Standard Model. The last decade has witnessed a revolution of exciting discoveries such as the detection of high-energy neutrinos and gravitational waves. The scope for major developments in the next decades is dramatic, as we detail in this report.

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arXiv2022

A tower of hidden sectors: a general treatment and physics implications

An analysis of a tower of hidden sectors coupled to each other, with one of these hidden sectors coupled to the visible sector, is given and the implications of such couplings on physics in the visible sector are investigated. Thus the analysis considers $n$ number of hidden sectors where the visible sector couples only to hidden sector 1, while the latter couples also to hidden sector 2, and the hidden sector 2 couples to hidden sector 3 and so on. A set of successively feeble couplings of the hidden sectors to the visible sector are generated in such a set up. In general each of these sectors live in a different heat bath. We develop a closed form set of coupled Boltzmann equations for the correlated evolution of the temperatures and number densities of each of the heat baths. We then apply the formalism to a simplified model with scalar portals between the different sectors. Predictions related to dark matter direct detection experiments and future CMB probes of dark radiation are made.

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arXiv2022

Annual modulation of event rate and electron recoil energy in inelastic scattering direct detection experiments

In 2020 the XENON1T experiment observed an excess of events with an electron recoil energy $E_R$ in the range of $2\,$--$\,3\,$keV. Such an excess can arise from a variety of sources such as solar axions or a neutrino magnetic moment, but also from inelastic scattering of dark matter off the xenon atoms. The recoil energy of the electron then depends on the mass difference of the dark particles. In this paper we show that the annual modulation of both the event rate and the electron recoil energy provide important additional information that allows to distinguish among different theoretical explanations of the signal. To this end, we first extend the formalism of annual modulation to electronic recoils, inelastic dark matter scattering and the electron recoil energy. We then study a concrete theoretical model with two Dirac fermions and a dark photon. We take into account all relevant cosmological and experimental constraints on this model and apply it to the XENON1T and and XENONnT experiments with realistic detection thresholds, efficiencies and energy resolutions, fitting the main physical parameters of the model, i.e. the mass splitting and the electron scattering cross section. The discriminatory power of the additional information from the annual modulation of both the signal rate and the electron recoil energy is then demonstrated for XENONnT with a simplified model based on these main physical parameters. This more sensitive procedure compared to time-only modulation analyses can also serve as a template for other theoretical models with different dark matter candidates, mediators and cosmology. For the $U(1)$ model with two Dirac fermions fitting the XENON1T excess and the experimental conditions of XENONnT, taking into account the annual variation of the signal rate and recoil energy allows for a faster and more precise determination of the free model parameters.

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arXiv2022

Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies

In this paper we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant $H_0$, the $σ_8$--$S_8$ tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the $5.0\,σ$ tension between the {\it Planck} CMB estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the {\it Planck} CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density $Ω_m$, and the amplitude or rate of the growth of structure ($σ_8,fσ_8$). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the $H_0$--$S_8$ tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals.[Abridged]

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arXiv2022

Analyzing the Hubble tension through hidden sector dynamics in the early universe

The recent analysis from the SH0ES Collaboration has confirmed the existence of a Hubble tension between measurements at high redshift ($z> 1000$) and at low redshift ($z<1$) at the $5σ$ level with the low redshift measurement giving a higher value. In this work we propose a particle physics model that can help alleviate the Hubble tension via an out-of-equilibrium hidden sector coupled to the visible sector. The particles that populate the dark sector consist of a dark fermion, which acts as dark matter, a dark photon, a massive scalar and a massless pseudo-scalar. Assuming no initial population of particles in the dark sector, feeble couplings between the visible and the hidden sectors via kinetic mixing populate the dark sector even though the number densities of hidden sector particles never reach their equilibrium distribution and the two sectors remain at different temperatures. A cosmologically consistent analysis is presented where a correlated evolution of the visible and the hidden sectors with coupled Boltzmann equations involving two temperatures, one for the visible sector and the other for the hidden sector, is carried out. The relic density of the dark matter constituted of dark fermions is computed in this two-temperature formalism. As a consequence, BBN predictions are upheld with a minimal contribution to $ΔN_{\rm eff}$. However, the out-of-equilibrium decay of the massive scalar to the massless pseudo-scalar close to the recombination time causes an increase in $ΔN_{\rm eff}$ that can help weaken the Hubble tension.

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arXiv2021

Tests of gluino-driven radiative breaking of the electroweak symmetry at the LHC

The recent muon $g-2$ result from Fermilab combined with the Brookhaven result, strongly points to new physics beyond the Standard Model which can be well described by the electroweak sector of supersymmetry if the masses of the sleptons and some of the electroweak gauginos are in the few hundred GeV range. However, the Higgs boson mass measurement at 125 GeV indicates a mass scale for squarks which lies in the few TeV region indicating a split mass spectrum between squarks and sleptons. This apparent puzzle is resolved in a natural way in gluino-driven radiative breaking of the electroweak symmetry where radiative breaking is driven by a large gluino mass and the gluino color interactions lead to a large splitting between the squarks and the sleptons. We show that an analysis without prejudice using an artificial neural network also leads to the gluino-driven radiative breaking. We use a set of benchmarks and a deep neural network analysis to test the model for the discovery of light sleptons and sneutrinos at HL-LHC and HE-LHC.

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arXiv2021

A cosmologically consistent millicharged dark matter solution to the EDGES anomaly of possible string theory origin

Analysis of EDGES data shows an absorption signal of the redshifted 21-cm line of atomic hydrogen at $z\sim 17$ which is stronger than expected from the standard $Λ$CDM model. The absorption signal interpreted as brightness temperature $T_{21}$ of the 21-cm line gives an amplitude of $-$500$_{-500}^{+200}$ mK at 99\% C.L. which is a 3.8$σ$ deviation from what the standard $Λ$CDM cosmology gives. We present a particle physics model for the baryon cooling where a fraction of the dark matter resides in the hidden sector with a $U(1)$ gauge symmetry and a Stueckelberg mechanism operates mixing the visible and the hidden sectors with the hidden sector consisting of dark Dirac fermions and dark photons. The Stueckelberg mass mixing mechanism automatically generates a millicharge for the hidden sector dark fermions providing a theoretical basis for using millicharged dark matter to produce the desired cooling of baryons seen by EDGES by scattering from millicharged dark matter. We compute the relic density of the millicharged dark matter by solving a set of coupled equations for the dark fermion and dark photon yields and for the temperature ratio of the hidden sector and the visible sector heat baths. For the analysis of baryon cooling, we analyze the evolution equations for the temperatures of baryons and millicharged dark matter as a function of the redshift. We exhibit regions of the parameter space which allow consistency with the EDGES data. We note that the Stueckelberg mechanism arises naturally in strings and the existence of a millicharge would point to its string origin.

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