arXiv subjects

Yu-Cheng Qiu

Publications and source records attributed to Yu-Cheng Qiu.

At least 19 recordsLinked to original sources

arXiv2026

A quality-coupling relation in chiral $U(1)_{B-L}$ axion model

The quality of the QCD axion can be protected by a gauge symmetry. This work considers a gauged chiral $U(1)_{B-L}$. The vacuum expectation values of two complex scalars break $U(1)_{B-L}$. One linear combination of their two phase degrees of freedom is eaten by the $U(1)_{B-L}$ gauge boson, while the other becomes the QCD axion. Since the PQ symmetry is accidental, there is no ambiguity in the PQ charge assignment. High axion quality implies a large anomalous coupling between the axion and the $U(1)_{B-L}$ gauge boson (or gauged Majoron). A `quality floor', namely a minimal coupling determined by the axion quality, arises for the coupling between the axion and SM fermions, extending the parameter space of QCD axions toward improved testability.

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arXiv2026

Looking for Lights from the Darkness: Signals from MeV-scale Solar Axion-like Particles

The axion-like particles $a$ can be produced in the Sun via the process of $p + D \to {}^3{\rm He} +a$, with mass up to 5.5 MeV. The photons in the subsequent decay $a \to \gamma\gamma$ can deviate significantly from the Sun, or even from roughly the opposite direction of the Sun. The nontrivial angular and spectral distributions of such photons enable us new methods to detect the {\it lights from the darkness}. In this letter, we consider both the space detection and terrestrial experiments at the South Pole. As a result of the two-body decay and the geometric effects, there exists a critical height for the terrestrial experiments, below which there is no photon for some regions of the parameter space. With the sensitivities of $10^{-16}$ ($10^{-17}$) erg cm$^{-2}$ s$^{-1}$ for the MeV-scale photons in future space and terrestrial experiments, the coupling $g_{a\gamma}$ of $a$ to photons can be probed up to $3\times10^{-12}$ ($1\times10^{-12}$) GeV$^{-1}$, well surpassing the current supernova limits.

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arXiv2025

High Reheating Temperature without Axion Domain Walls

We investigate a cosmological scenario in which the Peccei-Quinn (PQ) symmetry remains broken in the entire history of the Universe, thereby avoiding the formation of axion strings and domain walls. Contrary to the conventional expectation, it is demonstrated that appropriately chosen scalar interactions are able to keep the PQ symmetry broken at arbitrarily high temperatures. We carefully examine the finite-temperature effective potential in a model with two PQ breaking scalar fields. The existence of flat directions plays a vital role in suppressing axion isocurvature perturbations during inflation by stabilizing a PQ field at a large field value. The viable parameter space consistent with theoretical and observational constraints is identified. Our scenario provides a minimal path for PQ symmetry breaking that addresses both the axion domain wall and isocurvature problems while permitting arbitrarily high reheating temperatures accommodating high-scale baryogenesis scenarios such as thermal leptogenesis.

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arXiv2025

The Lifespan of our Universe

The Dark Energy Survey (DES) and the Dark Energy Spectroscopic Instrument (DESI) measurements claim that the dark energy equation of state $w \ne -1$. This observation can be explained by the axion Dark Energy (aDE) model of an ultralight axion plus a cosmological constant $\Lambda$. Despite a relatively large degeneracy, there is a high probability that $\Lambda <0$. This negative $\Lambda$ leads the universe to end in a big crunch. Using the best-fit values of the model as a benchmark, we find the lifespan of our universe to be 33 billion years.

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arXiv2025

Quest for a phenomenologically consistent low cutoff theory

The Randall-Sundrum model with the Higgs localized on the IR brane solves the gauge hierarchy problem. However, the associated low cutoff ($\Lambda \sim 10$ TeV) generically leads to unacceptably rapid nucleon decay and excessively large Majorana neutrino masses. Achieving consistency while simultaneously explaining the Yukawa hierarchy requires either a horizontal symmetry or a discrete gauged symmetry. We demonstrate that eliminating all dangerous operators within a horizontal symmetry framework must come with large and unattractive charge assignments, if possible at all. Hence, we consider an exact discrete gauged $\mathbf{Z}_N$ symmetry, with fermion mass hierarchies generated via wave function overlap. We employ this to reproduce the current Cabibbo-Kobayashi-Maskawa and Pontecorvo-Maki-Nakagawa-Sakata structures. Assuming universal five-dimensional Yukawa couplings, generation-blind profile for right-handed neutrinos and flat profile for the third generation SM doublets, it predicts Dirac neutrinos with a total mass $\sim 66$ meV. Since the $\mathbf{Z}_N$ charges must be generation blind, flavor observables serve as key probes.

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arXiv2025

Interpreting Cosmic Birefringence and DESI Data with Evolving Axion in $\Lambda$CDM

Recent cosmological observations have revealed growing tensions with the standard $\Lambda$CDM model, including indications of isotropic cosmic birefringence and deviations from $w = -1$ in the dark energy equation of state, as suggested by DESI and supernova measurements. In this paper, we point out that such deviations can arise even from a subdominant energy density component. We then propose a unified framework based on a dynamical axion field that simultaneously accounts for both anomalies, providing a simple and natural extension of the standard $\Lambda$CDM model. In our scenario, the axion field with $2H_0\lesssim m\lesssim 6H_0$, where $H_0$ is the current Hubble constant, induces a nonzero rotation of the CMB polarization plane and modifies the present-day dark energy equation of state. This framework accommodates recent observational data with natural parameter choices, even for a string axion with a decay constant of order $10^{17}\,$GeV.

astro-ph.CO↗

arXiv2025

Dynamical dark energy from an ultralight axion

Recently the Dark Energy Survey (DES) Collaboration presented evidence that the equation of state $w$ of the dark energy is varying, or $w \simeq -0.948$ if it is constant. In either case, the dark energy cannot be due to a cosmological constant alone. Here we study an ultralight axion (or axion-like particle) with mass $m_\phi \simeq 2 \times 10^{-33}$ eV that has properties that can explain the new $w$ measurement. In particular, $w\ge -1$ and a negative cosmological constant $\Lambda < 0$ is preferred in this model. We also present a simple formula for $w$ for the model to ease data fitting.

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arXiv2024

Wiggly dilaton: a landscape of spontaneously broken scale invariance

The dilaton emerges as a pseudo-Nambu-Goldstone boson (pNGB) associated with the spontaneous breaking of scale invariance in a nearly conformal field theory (CFT). We show the existence of a wiggly dilaton potential that contains multiple vacuum solutions in a five-dimensional (5D) holographic formulation. The wiggly feature originates from boundary potentials of a 5D axion-like scalar field, whose naturally small bulk mass parameter corresponds to a marginally-relevant deformation of the dual CFT. Depending on the energy density of a boundary 3-brane, our model can provide a relaxion potential or generate a light dilaton. However, an extremely light dilaton requires fine-tuning.

hep-th↗

arXiv2024

Gemini Dark Matter

The $S_8/\sigma_8$ tension in the large scale structure can be explained by decaying dark matter with an almost degenerate spectrum and small enough decay width. Here we propose the Gemini dark matter model, which contains a heavy mother particle $\chi_3$ and two twins $\chi_{1/2}$ which are almost degenerate in mass and are produced at the same time. The dark sector is charged under the same Froggatt-Nielsen symmetry that can explain the hierarchy of the Standard model Yukawa couplings. The slightly heavier $\chi_2$ decays into $\chi_1$ and the axionic component of the flavon, which washes out the small scale structure and resolves $S_8/\sigma_8$ tension. We present the production mechanism of Gemini dark matter and viable parameter regions. We find that despite the preferred dark matter mass being $\mathcal{O}(1)$--$\mathcal{O}(100)$ keV, they constitute cold dark matter. The Gemini dark matter model predicts an abundance of dark radiation that will be probed in future measurements of the cosmic microwave background.

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arXiv2024

Large CP Violation from the Minimum Seesaw Model

The minimum seesaw model with two right-handed neutrinos is considered, where the lightest neutrino is naturally massless. Instead of adopting texture zeros in the lepton Yukawa matrices, which cause both theoretical and experimental troubles, here we propose two-$\boldsymbol\epsilon$ textures, where $\boldsymbol\epsilon$ is a small number. Combined with neutrino oscillation experimental data, we find that a large CP angle is preferred for the normal neutrino mass order. In contrast, the CP angle almost vanishes for the inverted order. This can be well-tested in near-future experiments, such as Hyper-Kamiokande. Besides, the predicted effective Majorana neutrino mass $m_{ee}$ and the total neutrino mass $\sum m^\nu_i$ are also within reach of ongoing or future experiments.

hep-ph↗

arXiv2024

Can we explain cosmic birefringence without a new light field beyond Standard Model?

The recent analysis of the Planck 2018 polarization data shows a nonzero isotropic cosmic birefringence (ICB) that is not explained within the $Λ$CDM paradigm. We then explore the question of whether the nonzero ICB is interpreted by the framework of the Standard Model Effective Field Theory (SMEFT), or at the energy scales of the cosmic microwave background, the low-energy EFT (LEFT) whose dynamical degrees of freedom are five SM quarks and all neutral and charged leptons. Our systematic study reveals that any operator in the EFT on a cosmological background would not give the reported ICB angle, which is observationally consistent with frequency independence. In particular, we estimate the size of the ICB angle generated by the effect that the cosmic microwave background photons travel through the medium of the cosmic neutrino background with parity-violating neutrino-photon interactions and find that it would be too small to explain the data. If the reported ICB angle should be confirmed, then our result would indicate the existence of a new particle that is lighter than the electroweak scale and feebly interacting with the SM particles.

astro-ph.CO↗

arXiv2023

Ultraheavy Atomic Dark Matter Freeze-Out through Rearrangement

Atomic dark matter is usually considered to be produced asymmetrically in the early Universe. In this work, we first propose that the symmetric atomic dark matter can be thermally produced through the freeze-out mechanism. The dominant atom anti-atom annihilation channel is the atomic rearrangement. It has a geometrical cross section much larger than that of elementary fermions. After the atomic formation, this annihilation process further depletes dark matter particles and finally freezes out. To give the observed dark matter relic, the dark atoms are naturally ultraheavy, ranging from $10^6$ to $10^{10} \,\mathrm{GeV}$.

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arXiv2023

Predictions of $m_{ee}$ and neutrino mass from a consistent Froggatt-Nielsen model

The seesaw mechanism is the most attractive mechanism to explain the small neutrino masses, which predicts the neutrinoless double beta decay ($0νββ$) of the nucleus. Thus the discovery of $0νββ$ is extremely important for future particle physics. However, the present data on the neutrino oscillation is not sufficient to predict the value of $m_{ee}$ as well as the neutrino mass $m_ν^i$. In this short article, by adopting a simple and consistent Froggatt-Nielsen model, which can well explain the observed masses and mixing angles of quark and lepton sectors, we calculate the distribution of $m_{ee}$ and $m_ν^i$. Interestingly, a relatively large part of the preferred parameter space can be detected in the near future.

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arXiv2023

Baryon Number Violating Rate as A Function of the Proton-Proton Collision Energy

The baryon-number violation (BV) happens in the standard electroweak model. According to the Bloch-wave picture, the BV event rate shall be significantly enhanced when the proton-proton collision center of mass (COM) energy goes beyond the sphaleron barrier height $E_{\rm sph}\simeq 9.0\,{\rm TeV}$. Here we compare the BV event rates at different COM energies, using the Bloch-wave band structure and the CT18 parton distribution function data, with the phase space suppression factor included. As an example, the BV cross section at 25 TeV is 4 orders of magnitude bigger than its cross section at 13 TeV. The probability of detection is further enhanced at higher energies since an event at higher energy will produce on average more same sign charged leptons.

hep-ph↗

arXiv2023

The Hubble Constant in the Axi-Higgs Universe

The $Λ$CDM model provides an excellent fit to the CMB data. However, a statistically significant tension emerges when its determination of the Hubble constant $H_0$ is compared to the local distance-redshift measurements. The axi-Higgs model, which couples an ultralight axion to the Higgs field, offers a specific variation of the $Λ$CDM model. It relaxes the $H_0$ tension as well as explains the $^7$Li puzzle in Big-Bang nucleosynthesis, the clustering $S_8$ tension with the weak-lensing data, and the observed isotropic cosmic birefringence in CMB. In this paper, we demonstrate how the $H_0$ and $S_8$ tensions can be relaxed simultaneously, by correlating the axion impacts on the early and late universe. In a benchmark scenario ($m=2 \times 10^{-30}$ eV) selected for experimental tests soon, the analysis combining the CMB+BAO+WL+SN data yields $H_0 = 69.9 \pm 1.5$ km/s/Mpc and $S_8 = 0.8045 \pm 0.0096$. Combining this (excluding the SN (supernovae) part) with the local distance-redshift measurements yields $H_0 = 72.42 \pm 0.76$ km/s/Mpc, while $S_8$ is slightly more suppressed.

astro-ph.CO↗

arXiv2023

High-quality axions in a class of chiral $U(1)$ gauge theories

We show that there are many candidates for the quintessence and/or the QCD axions in a class of chiral $U(1)$ gauge theories. Their qualities are high enough to serve as the dark energy and/or to solve the strong CP problem. Interestingly, the high quality of axion is guaranteed by the gauged $U(1)$ and $\mathbf{Z}_{2N}$ symmetries and hence free from the non-perturbative quantum gravity corrections. Furthermore, our mechanism can be easily applied to the Fuzzy dark matter axion scenarios.

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arXiv2023

Model of the quintessence axion

We construct a model of the quintessence axion based on a gauged chiral $U(1)$ symmetry and an additional flat fifth dimension. The required high qualities are guaranteed by the brane separation. The observed cosmological constant (i.e., the potential energy of the quintessence axion) is determined by the size of the extra dimension and the axion decay constant $F_a$ is fixed almost at $F_a\simeq10^{17}\,{\rm GeV}$, which is sufficiently large for the stability of the axion field near the hilltop of its potential. Furthermore, the movement of the axion can also easily explain the recently reported isotropic cosmic birefringence of the cosmic microwave background photon.

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arXiv2023

A Novel Solution to the Gravitino Problem

In a general phenomenological model with local supersymmetry, the amount of massive gravitinos produced in early universe tends to violate the known dark matter density bound by many orders of magnitude. In the brane world scenario in Type IIB string theory, we propose a novel way to evade this problem. There, the standard model of strong and electroweak interactions live inside the anti-${\rm D3}$-branes ($\overline{\rm D3}$-branes) that span the 3 large spatial dimensions. Here, the "potential" Goldstino to be absorbed by the gravitino (to become massive) is the fermion component of the open string nilpotent superfield $X$ (i.e., $X^2=0$) which is present only inside the $\overline{\rm D3}$-branes. This non-linear supergravity scenario offers 2 ways to solve the gravitino problem, with very different particle physics phenomenologies.

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