arXiv subjects

Erdenebulgan Lkhagvadorj

Publications and source records attributed to Erdenebulgan Lkhagvadorj.

6 recordsLinked to original sources

arXiv2026

Leptogenesis and Planck-scale black hole remnants in a Pati-Salam cosmology

We study leptogenesis and Planck-scale remnant dark matter from primordial black hole (PBH) evaporation in a minimal Pati-Salam cosmology, with the gauge symmetry broken before inflation so that magnetic monopoles are diluted away. A singlet inflaton with a near-inflection potential enhances the curvature power spectrum on small scales, producing a narrow black hole population that briefly dominates the energy density. The Pati-Salam embedding ties the right-handed neutrino masses to the SU(2)_R breaking scale, and cosmological consistency forces both the scalar-sector Yukawa coupling and the heavy neutrino mass well below that scale. Two regimes emerge, depending on whether the black holes are hot enough to emit the lightest right-handed neutrino. Lighter PBHs drive non-thermal leptogenesis, while heavier ones require a thermal asymmetry and also affect it through entropy dilution. If quantum gravitational backreaction halts evaporation at the Planck scale, each PBH leaves a stable remnant whose present abundance scales as the inverse five-halves power of the initial mass. Suppressing remnants requires heavier black holes, but the lighter PBHs needed for non-thermal leptogenesis overproduce remnant dark matter. Thus, remnant dark matter and non-thermal leptogenesis are mutually exclusive. When the thermal contribution is included, a single initial PBH mass near 10^6 g accommodates the observed dark matter abundance, the heavy neutrino mass required by the baryon asymmetry, and the Pati-Salam breaking scale. The scenario predicts a stochastic gravitational wave background from Poisson fluctuations of the black hole distribution, within reach of future experiments, alongside high-frequency graviton emission constrained by future measurements of the effective number of relativistic species.

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arXiv2026

Scalar Portal Verifiable Light Dark Matter and Correlated Gravitational Wave Signatures

The lack of signals in direct detection experiments has placed the canonical Weakly Interacting Massive Particle (WIMP) paradigm under severe tension, motivating a shift toward the sub-GeV Light Dark Matter (LDM) regime. However, realizing detectable LDM interaction rates typically requires large couplings to the visible sector, which leads to a severe thermal underabundance of the dark matter relic density within standard cosmology. Furthermore, LDM models featuring vector mediators face stringent constraints from the Cosmic Microwave Background (CMB) due to late-time energy injection. In this work, we propose a minimal scalar portal extension featuring a vector-like fermion dark matter candidate, which naturally evades CMB bounds via inherent p-wave annihilation suppression. To simultaneously achieve the correct relic density and large direct-detection couplings, we invoke a pre-Big Bang Nucleosynthesis (BBN) non-standard cosmology dominated by a stiff fluid ($w > 1/3$). The enhanced Hubble expansion during this epoch triggers an early dark matter freeze-out, successfully rescuing the asymptotic relic abundance. Crucially, this stiff pre-BBN phase heavily blue-shifts inflationary gravitational waves that re-enter the horizon prior to BBN, imprinting a distinct high-frequency tilt on the stochastic gravitational wave background. We establish a robust correlation between the non-standard expansion history, the particle physics parameters verifiable in future terrestrial direct detection experiments, and the unique gravitational wave signatures observable by forthcoming space-based interferometers like LISA and DECIGO. This framework highlights how multi-messenger observations can concurrently probe the dark sector and the pre-BBN thermal history of the Universe.

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arXiv2025

Cosmological Origin of the KM3-230213A event and associated Gravitational Waves

We propose a novel cosmological scenario to explain the exceptional KM3-230213A neutrino event reported at an energy scale of $\mathcal{O}(100)$~PeV by the KM3NeT collaboration, along with its associated gravitational wave (GW) signatures. In our framework, ultra high energy neutrinos originate from the decay of a super-heavy sterile neutrino produced via the Hawking evaporation of primordial black holes (PBHs) in the early Universe. Employing an ultraviolet complete type-I seesaw model, we demonstrate that while two sterile neutrinos are responsible for light neutrino masses as required by oscillation data, one sterile neutrino can have an exceedingly feeble coupling, allowing its lifetime to be tuned so that its decay yields a neutrino flux consistent with the observed event. Furthermore, our scenario predicts two distinct GW signatures: one arising from gravitons emitted during PBH evaporation and another from the Bremsstrahlung process during the decay of the sterile neutrino. These complementary signals provide a multi-messenger probe of the underlying physics. Our results thus offer a compelling explanation for the KM3-230213A event and open new avenues for investigating the interplay between high-energy neutrino astronomy and gravitational wave cosmology.

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arXiv2024

Gravitational Wave Sourced by Decay of Massive Particle from Primordial Black Hole evaporation

In this article, we investigate the stochastic gravitational waves (GWs) spectrum, resulting from the emission of gravitons through bremsstrahlung, in the decay of particles produced by Hawking radiation. Although particle decays inevitably entail the emission of graviton due to bremsstrahlung, the associated decay width is notably suppressed due to the Planck scale suppression in the coupling of matter fields to gravitons. Consequently, the relic abundance of such GWs constituted of these gravitons undergoes a corresponding reduction. However, we demonstrate that super-heavy particles, reaching masses as high as Planck scale, can emerge naturally in the Hawking radiation of evaporating primordial black holes (PBHs) and can compensate for this suppression. In addition, we also discuss the stochastic gravitational waves constituted out of the gravitons directly radiated from such evaporating PBHs. When the super-heavy particle decays promptly after its production, then the corresponding GW spectrum remains subdominant to the one arising from direct PBH evaporation. However, if this particle is long-lived and decays after PBH evaporation, then the resulting GWs produced in these two processes have two distinct spectra with their peaks at extremely high frequencies, providing avenues for proposed ultra-high frequency gravitational wave detectors. We also show that such gravitational waves contribute significantly to substantial dark radiation, which can be probed with the enhanced sensitivity of future experiments.

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arXiv2024

Non-thermal WIMPy Baryogenesis with Primordial Black Hole

We consider the possibility that the weakly interacting massive particles produced from the evaporation of primordial black hole can explain both the relic density of dark matter and the baryon asymmetry of the Universe, through their annihilation which violate B and CP-symmetry. We find that the primordial black hole with mass less than $10^7 {\rm g}$ is a good candidate as an source of TeV dark matter with the total annihilation cross section $\left\langleσ_a \upsilon\right\rangle \lesssim 10^{-7} \ {\rm GeV}^{-2}$ and the B-violating scattering cross section $\left\langleσ_B \upsilon\right\rangle \lesssim 2\times 10^{-9} \ {\rm GeV^{-2}}$. This large annihilation cross section of dark matter in this model would make it available to search them in the indirect search for dark matter such as gamma-ray or neutrino observations.

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arXiv2023

Probing sterile neutrino dark matter in the PTOLEMY-like experiment

We study the prospect to detect the cosmic background of sterile neutrinos in the Tritium $β$-decay, such as PTOLEMY-like experiments. The sterile neutrino with mass between 1 eV - 10 keV may contribute to the local density as warm or cold DM component. In this study, we investigate the possibility for searching them in the models with different production in the early Universe, without assuming sterile neutrino as full dark matter component. In these models, especially with low-reheating temperature or phase transition, the capture rate per year can be greatly enhanced to be $\mathcal O(10)$ without violating other astrophysical and cosmological observations.

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