130 citations · 934 across the 27 of their papers we have counts for
27 papers
Gravitational Waves from Multiple First-Order Phase Transitions in a Scenario with Early Matter Domination
Rouzbeh Allahverdi, Fazlollah Hajkarim
Non-standard cosmological histories with epochs of early matter domination (EMD) arise in various top-down models of the early universe. Typically, in the latter stage of EMD, temp…
Worth the Effort? An Examination on the Effect of Higher Diligence Calculations of the Sound Shell Model
Fazlollah Hajkarim, Graham White, Yang Xiao
The gravitational wave spectrum arising from using the full velocity profile is well known to differ qualitatively from analytic fits to a broken power law. Former studies have sho…
Oscillations and parity violation in gravitational wave background from extra tensor modes
Jaume Garriga, Mohammad Ali Gorji, Fazlollah Hajkarim +1
Spectator fields which provide additional tensor degrees of freedom, on top of the standard metric tensor perturbations, can produce significant amounts of gravitational waves (GWs…
Supernova-Boosted Dark Matter at Large-Volume Neutrino Detectors
Badal Bhalla, Fazlollah Hajkarim, Doojin Kim +1
Core-collapse supernovae, among the universe's most energetic events, offer a novel window into the dark sector by potentially producing a flux of boosted dark matter (BDM). We exp…
Primordial Gravitational Waves from Phase Transitions during Reheating
Amitayus Banik, Nicolás Bernal, Fazlollah Hajkarim
We study primordial gravitational waves (GWs) generated from first-order phase transitions (PTs) during cosmic reheating. Using a minimal particle physics model, and a general para…
QUPITER -- Space Quantum Sensors for Jovian-Bound Dark Matter
Yu-Dai Tsai, Fazlollah Hajkarim
We propose utilizing space quantum sensors to detect ultralight dark matter (ULDM) bound to planetary bodies, focusing on Jupiter as the heaviest planet in the solar system. Levera…
Thermodynamic Consistent Description of Compact Stars of Two Interacting Fluids: The Case of Neutron Stars with Higgs Portal Dark Matter
Fazlollah Hajkarim, Jürgen Schaffner-Bielich, Laura Tolos
We consider a thermodynamically consistent approach for the computation of the masses, radii, and tidal deformabilities of compact stars consisting of two interacting fluids with s…
A Precise Fitting Formula for Gravitational Wave Spectra from Phase Transitions
Huai-ke Guo, Fazlollah Hajkarim, Kuver Sinha +2
Obtaining a precise form for the predicted gravitational wave (GW) spectrum from a phase transition is a topic of great relevance for beyond Standard Model (BSM) physicists. Curren…
New Constraints on Axion-Like Particles from IXPE Polarization Data for Magnetars
Ephraim Gau, Fazlollah Hajkarim, Steven P. Harris +4
We derive new constraints on axion-like particles (ALPs) using precision -ray polarization studies of magnetars. Specifically, we use the first detection of polarized -rays f…
Dark Radiation from the Primordial Thermal Bath in Momentum Space
Francesco D'Eramo, Fazlollah Hajkarim, Alessandro Lenoci
Motivated by the stunning projections for future CMB surveys, we evaluate the amount of dark radiation produced in the early Universe by two-body decays or binary scatterings with…
Did we hear the sound of the Universe boiling? Analysis using the full fluid velocity profiles and NANOGrav 15-year data
Tathagata Ghosh, Anish Ghoshal, Huai-Ke Guo +5
In this paper, we analyse sound waves arising from a cosmic phase transition where the full velocity profile is taken into account as an explanation for the gravitational wave spec…
Lepton and -boson mass anomalies in the DFSZ axion model
Moslem Ahmadvand, Fazlollah Hajkarim
With regard to the leptonic magnetic dipole moment anomaly as well as the -boson mass excess, we study the DFSZ axion model. Considering theoretical and experimental constraints…
Probing Axions via Light Circular Polarization and Event Horizon Telescope
Soroush Shakeri, Fazlollah Hajkarim
The impact of axion-like particles on the light polarization around the horizon of suppermassive black hole (SMBH) is discussed in the light of the latest polarization measurement…
Cosmological Bound on the QCD Axion Mass, Redux
Francesco D'Eramo, Eleonora Di Valentino, William Giarè +5
We revisit the joint constraints in the mixed hot dark matter scenario in which both thermally produced QCD axions and relic neutrinos are present. Upon recomputing the cosmologica…
Thermal QCD Axions across Thresholds
Francesco D'Eramo, Fazlollah Hajkarim, Seokhoon Yun
Thermal axion production in the early universe goes through several mass thresholds, and the resulting rate may change dramatically across them. Focusing on the KSVZ and DFSZ frame…
Thermal axion production at low temperatures: a smooth treatment of the QCD phase transition
Francesco D'Eramo, Fazlollah Hajkarim, Seokhoon Yun
We study thermal axion production around the confinement scale. At higher temperatures, we extend current calculations to account for the masses of heavy quarks, whereas we quantif…
Axion Dark Matter in the Time of Primordial Black Holes
Nicolás Bernal, Fazlollah Hajkarim, Yong Xu
We investigate the production of QCD axion dark matter in a nonstandard cosmological era triggered by primordial black holes (PBHs) that fully evaporate before the onset of BBN. Ev…
Pion condensation in the early Universe at nonvanishing lepton flavor asymmetry and its gravitational wave signatures
Volodymyr Vovchenko, Bastian B. Brandt, Francesca Cuteri +3
We investigate the possible formation of a Bose-Einstein condensed phase of pions in the early Universe at nonvanishing values of lepton flavor asymmetries. A hadron resonance gas…
Shedding New Light on Sterile Neutrinos from XENON1T Experiment
Soroush Shakeri, Fazlollah Hajkarim, She-Sheng Xue
The XENON1T collaboration recently reported the excess of events from recoil electrons, possibly giving an insight into new area beyond the Standard Model (SM) of particle physics.…
Primordial Gravitational Wave Signals in Modified Cosmologies
Nicolás Bernal, Anish Ghoshal, Fazlollah Hajkarim +1
Modified expansion rates in the early Universe prior to big bang nucleosynthesis are common in modified gravity theories, and can have a significant impact on the generation of dar…
Thermal History of the Early Universe and Primordial Gravitational Waves from Induced Scalar Perturbations
Fazlollah Hajkarim, Jürgen Schaffner-Bielich
We study the induced primordial gravitational waves (GW) coming from the effect of scalar perturbation on the tensor perturbation at the second order of cosmological perturbation t…
Effects of the QCD Equation of State and Lepton Asymmetry on Primordial Gravitational Waves
Fazlollah Hajkarim, Jürgen Schaffner-Bielich, Stephan Wystub +1
Using the quantum chromodynamics (QCD) equation of state (EoS) from lattice calculations we investigate effects from QCD on primordial gravitational waves (PGWs) produced during th…
Primordial Gravitational Waves in Nonstandard Cosmologies
Nicolás Bernal, Fazlollah Hajkarim
Assuming that inflation is followed by a phase where the energy density of the Universe is dominated by a component with a general equation of state, we evaluate the spectrum of pr…
On the viability of Planck scale cosmology with quartessence
Mohsen Khodadi, Kourosh Nozari, Fazlollah Hajkarim
In this paper, using a qualitative theory of dynamical systems, we study the stability of a unified dark matter-dark energy framework known as quartessence Chaplygin model (QCM) wi…