arXiv subjects

Gongjun Choi

Publications and source records attributed to Gongjun Choi.

35 records · Page 2Linked to original sources

arXiv2021

The Upper Bound of the Second Higgs Boson Mass in Minimal Gauge Mediation with the Gravitino Warm Dark Matter

A keV-scale gravitino arsing from a minimal supersymmetric (SUSY) Standard Model (MSSM) is an interesting possibility since the small scale problems that $Λ$CDM model encounters in the modern cosmology could be alleviated with the keV-scale gravitino serving as the warm dark matter (WDM). Such a light gravitino asks for a low scale supersymmetry (SUSY) breaking for which the gauge mediation (GM) is required as a consistent SUSY-breaking mediation mechanism. In this paper, we show upperbounds of the masses of the second CP-even Higgs boson $H$ and the CP-odd Higgs boson $A$, assuming the keV-scale gravitino to be responsible for the current DM relic abundance: the upperbound on the mass of $H/A$ is found to be $\sim 4$ TeV for the gravitino mass of $\mathcal{O}(10$-$100)$ keV. Interestingly, the mass of $H/A$ can be as small as 2-3 TeV and the predicted $\tanβ$ is as large as 55-60 for the gravitino mass of $\mathcal{O}(10)$ keV. This will be tested in the near future Large Hadron Collider (LHC) experiments.

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arXiv2021

Charms of Strongly Interacting Conformal Gauge Mediation

By extending a previously proposed conformal gauge mediation model, we construct a gauge-mediated SUSY breaking (GMSB) model where a SUSY-breaking scale, a messenger mass, the $μ$-parameter and the gravitino mass in a minimal supersymmetric (SUSY) Standard Model (MSSM) are all explained by a single mass scale, a R-symmetry breaking scale. We focus on a low scale SUSY-breaking scenario with the gravitino mass $m_{3/2}=\mathcal{O}(1){\rm eV}$, which is free from the cosmological gravitino problem and relaxes the fine-tuning of the cosmological constant. Both the messenger and SUSY-breaking sectors are subject to a hidden strong dynamics with the conformality above the messenger mass threshold (and hence the name of the model "strongly interacting conformal gauge mediation"). In our model, the Higgs B-term is suppressed and a large $\tanβ$ is predicted, resulting in the relatively light second CP-even Higgs and the CP-odd Higgs with a sizable production cross section. These Higgs bosons can be tested at future LHC experiments.

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arXiv2021

A Model of Interacting Dark Matter and Dark Radiation for $H_{0}$ and $σ_{8}$ Tensions

We present a model describing the dark sector (DS) featured by two interactions remaining efficient until late times in the matter-dominated era after recombination: the interaction among dark radiations (DR), and the interaction between a small fraction of dark matter and dark radiation. The dark sector consists of (1) a dominant component cold collisionless DM (DM1), (2) a sub-dominant cold DM (DM2) and (3) a self-interacting DR. When a sufficient amount of DR is ensured and a few percent of the total DM density is contributed by DM2 interacting with DR, this set-up is known to be able to resolve both the Hubble and $σ_{8}$ tension. In light of this, we propose a scenario which is logically natural and has an intriguing theoretical structure with a hidden unbroken gauge group ${\rm SU}(5)_{\rm X}\otimes {\rm U}(1)_{\rm X}$. Our model of the dark sector does not introduce any new scalar field, but contains only massless chiral fermions and gauge fields in the ultraviolet (UV) regime. As such, it introduces a new scale (DM2 mass, $m_{\rm DM2}$) based on the confinement resulting from the strong dynamics of ${\rm SU}(5)_{\rm X}$. Both DM2-DR and DR-DR interactions are attributed to an identical long range interaction of ${\rm U}(1)_{\rm X}$. We show that our model can address the cosmological tensions when it is characterized by $g_{\rm X}=\mathcal{O}(10^{-3})-\mathcal{O}(10^{-2})$, $m_{\rm DM2}=\mathcal{O}(1)-\mathcal{O}(100){\rm GeV}$ and $T_{\rm DS}/T_{\rm SM}\simeq0.3-0.4$ where $g_{\rm X}$ is the gauge coupling of ${\rm U}(1)_{\rm X}$ and $T_{\rm DS}$ ($T_{\rm SM}$) is a temperature of the DS (Standard Model sector). Our model explains candidates of DM2 and DR, and DM1 can be any kind of CDM.

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arXiv2021

Dark Photon Dark Matter in the minimal $B-L$ Model

The extension of the Standard model (SM) with three heavy right handed neutrinos, a complex scalar and the gauged $U(1)_{\rm B-L}$ symmetry (the minimal $B-L$ model) is considered the most compelling minimal one: the presence and the out-of-equilibrium decay of the heavy right handed neutrinos can account for the small masses of the active neutrinos and the baryon asymmetry of the universe. A natural accompanying question concerns whether the minimal $B-L$ model can naturally accommodate an interesting dark matter (DM) candidate. We study the possibility where the current DM population is explained by the gauge boson of $U(1)_{\rm B-L}$ symmetry. We discuss how the minimal set-up originally aimed at the seesaw mechanism and the leptogenesis is connected to conditions making the gauge boson promoted to a DM candidate.

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arXiv2020

Feebly Interacting $U(1)_{\rm B-L}$ Gauge Boson Warm Dark Matter and XENON1T Anomaly

The recent observation of an excess in the electronic recoil data by the XENON1T detector has drawn many attentions as a potential hint for an extension of the Standard Model (SM). Absorption of a vector boson with the mass of $m_{A'}\!\in\!(2\,{\rm keV},\!3\,{\rm keV})$ is one of the feasible explanations to the excess. In the case where the vector boson explains the dark matter (DM) population today, it is highly probable that the vector boson belongs to a class of the warm dark matter (WDM) due to its suspected mass regime. In such a scenario, providing a good fit for the excess, the kinetic mixing $κ\!\sim\!10^{-15}$ asks for a non-thermal origin of the vector DM. In this letter, we consider a scenario where the gauge boson is nothing but the $U(1)_{\rm B-L}$ gauge boson and its non-thermal origin is attributed to the decay of the coherently oscillating scalar of which condensation induces the spontaneous breaking of $U(1)_{\rm B-L}$. We discuss implications for the early universe physics when the warm nature of the vector DM serves as a resolution to both the small scale problems that $Λ$CDM model encounters and the XENON1T anomaly.

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arXiv2020

XENON1T Anomaly and its Implication for Decaying Warm Dark Matter

An excess in the electronic recoil data was observed in the XENON1T detector. One of plausible explanations for the excess is absorption of a vector bosonic particle with the mass of $2-3\,{\rm keV}$. For this, the kinetic mixing $κ\!\sim\!10^{-15}$ of the dark photon with the photon is required if the dark photon explains the current DM abundance. We recently proposed a model where the main component DM today is a decaying warm dark matter (WDM) with the life time comparable to the age of the current universe. The WDM decays to a massless fermion and a massive dark photon. This model was originally designed for addressing both the small scale problems which $Λ$CDM suffers from and the $H_{0}$ tension. In this letter, we show that the massive dark photon produced by the WDM decay can be identified with the vector boson inducing the anomalous excess in the XENON1T experiment. Depending on a lifetime of the parent decaying WDM, the dark photon could be either the main component or the sub-component of DM population today.

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arXiv2020

QCD Axion From a Spontaneously Broken B-L Gauge Symmetry

In this paper, we show that the Peccei-Quinn (PQ) symmetry with a good quality can be realized in a simple $B-L$ extension of the minimal supersymmetric standard model. The PQ symmetry is a remnant of the $B-L$ gauge symmetry at the renormalizable level. Besides, the sufficient quality of the PQ symmetry is preserved by a non anomalous discrete gauged $R$-symmetry and a small gravitino mass $m_{3/2}\ll 100$GeV. A viable mass range is $m_{3/2}=\mathcal{O}(1)$eV which allows a high reheating temperature and many baryogenesis scenarios typified by the thermal leptogenesis without any astrophysical and cosmological problems. Such a light gravitino may be tested in the future 21cm line observations.

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arXiv2020

Degenerate Sub-keV Fermion Dark Matter from a Solution to the Hubble Tension

We present a dark sector model addressing both the Hubble tension and the core-cusp problem. The model is based on a hidden Abelian gauge symmetry group with some chiral fermions required by the anomaly cancellation conditions, producing a candidate for the decaying fermion dark matter as a solution to the Hubble tension. Moreover, the sub-keV mass regime and the thermal history of the dark sector help the dark matter candidate resolve the core-cusp problem occurring in the standard $Λ$CDM cosmology.

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arXiv2020

Quintessence Axion Dark Energy and a Solution to the Hubble Tension

We present a model in which the question about a nature of the dark energy and the recently raised Hubble tension can be addressed at once. We consider the electroweak axion in the minimal supersymmetric standard model where the axion energy density is identified with the observed dark energy. Along with this, imposing a gauged $Z_{10}$ symmetry makes it possible to have a gravitino dark matter whose mass amounts to $\sim\mathcal{O}(1)\,\,{\rm GeV}$. We find that the gravitino with mass $\sim\mathcal{O}(1)\,\,{\rm GeV}$ can be a good candidate of a decaying dark matter of which decay after recombination can reconcile discrepancy in local measurements of the Hubble expansion rate $H_{0}$ and that inferred from the cosmic microwave background observation.

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arXiv2020

Degenerate Fermion Dark Matter from a Broken $U(1)_{\rm B-L}$ Gauge Symmetry

The extension of the Standard model by assuming $U(1)_{\rm B-L}$ gauge symmetry is very well-motivated since it naturally explains the presence of heavy right-handed neutrinos required to account for the small active neutrino masses via the seesaw mechanism and thermal leptogenesis. Traditionally, we introduce three right handed neutrinos to cancel the $[U(1)_{\rm B-L}]^3$ anomaly. However, it suffices to introduce two heavy right-handed neutrinos for these purposes and therefore we can replace one right-handed neutrino by new chiral fermions to cancel the $U(1)_{\rm B-L}$ gauge anomaly. Then, one of the chiral fermions can naturally play a role of a dark matter candidate. In this paper, we demonstrate how this framework produces a dark matter candidate which can address the so-called "core-cusp problem". As one of the small scale problems that $Λ$CDM paradigm encounters, it may imply an important clue for a nature of dark matter. One of resolutions among many is hypothesizing that sub-keV fermion dark matter halos in dwarf spheroidal galaxies are in (quasi) degenerate configuration. We show how the degenerate sub-keV fermion dark matter candidate can be non-thermally originated in our model and thus can be consistent with Lyman-$α$ forest observation. Thereby, the small neutrino mass, baryon asymmetry, and the sub-keV dark matter become consequences of the broken B-L gauge symmetry.

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arXiv2019

Probing Dynamics of Boson Stars by Fast Radio Bursts and Gravitational Wave Detection

Boson stars may consist of a new type of light singlet scalar particles with nontrivial self-interactions, and may compose a fraction of the dark matter in the Universe. In this work, we study the dynamics of boson stars with Liouville and logarithmic scalar self-interaction potentials as benchmarks. We perform a numerical analysis as well as a semi-analytic study on how the compactness and the total mass will deviate from that of the usual boson stars formed with a quartic repulsive self-interaction. We apply the recently suggested Swampland conjecture to examine whether boson stars with such benchmark potentials belong to the Landscape of a quantum gravity. Using the mass constraint on the macroscopic compact halo object (MACHO) and the cold dark matter (CDM) isocurvature mode constraint from the cosmic microwave background (CMB), we derive the allowed mass range of scalar particles which compose the boson star. We further analyze applications of the lensing of fast radio bursts (FRBs) and the gravitational wave (GW) detection to probe the presence of such boson stars and constrain the parameter space of their corresponding models. We discuss how the two types of boson star potentials can be discriminated by the FRB and GW measurements.

astro-ph.CO↗

arXiv2019

Solving the strong CP problem with horizontal gauge symmetry

We present a solution to the strong CP problem, which relies on the horizontal gauge symmetry and CP invariance in a full theory. Similar to other Nelson-Barr type solutions, CP violation in both the strong and weak sectors in the Standard model (SM) is attributed to the condensation of complex scalars $Φ$ in the model. The model is differentiated by others in that it explains the hierarchy in quark-Higgs Yukawa coupling in the SM based on a series of sequential breaking of the horizontal $SU(3)_{f}$ gauge symmetry. The experimental constraint $\overlineθ\lesssim10^{-10}$ requires $<\!\!Φ\!\!>\,\lesssim\,10^{13}-10^{14}{\rm GeV}$ (vacuum expectation value of complex scalars) and $λ\,\lesssim\,10^{-6}$ (scalar quartic coupling). We show that this small coupling is natural in the sense of 'tHooft naturalness. Compared to other models of Nelson-Barr type with CP breaking scale $Λ_{CP}\lesssim10^{8}{\rm GeV}$, our model is more advantageous in terms of consistency with the thermal leptogenesis.

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arXiv2018

Probing Decoupling in Dark Sectors with the Cosmic Microwave Background

The acoustic peaks in the angular power spectrum of cosmic microwave background (CMB) temperature and polarization anisotropies play an important role as a probe of the nature of new relativistic particles contributing to the radiation density in the early universe, parametrized by $ΔN_{eff}$. The amplitude and phase of the acoustic oscillations provide information about whether the extra species are free-streaming particles, like neutrinos, or tightly-coupled, like the photons, during eras probed by the CMB. On the other hand, some extensions of the Standard Model produce new relativistic particles that decouple from their own non-gravitational interactions after neutrinos, but prior to photons. We study the signature of new relativistic species that decouple during this intermediate epoch. We argue that the decoupling species will cause a scale-dependent change in the amplitude and phase shift of the acoustic oscillations, different from the usual constant shifts on small scales. For intermediate decoupling times, the phase and amplitude shifts depend not only on $ΔN_{eff}$ but the redshift $z_{dec,X}$ at which the new species decoupled. For $ΔN_{eff} >0.334$, a Stage IV CMB experiment could determine $N_{eff}$ at the percent level and $z_{dec,X}$ at the $\sim 10\%$ level. For smaller values, $ΔN_{eff}\sim 0.1$, constraints on $z_{dec,X}$ weaken but remain $\sim 20-50\%$ for $z_{dec,X} \sim \mathcal{O}(10^3-10^4)$. As an application, we study the contributions to $ΔN_{eff}$ and determine the $z_{dec,X}$ values for simple implementations of the so-called $N$naturalness model.

astro-ph.CO↗

arXiv2016

On the Question of a Possible Infrared Zero in the Beta Function of the Finite-$N$ Gross-Neveu Model

We investigate whether the beta function of the finite-$N$ Gross-Neveu model, as calculated up to the four-loop level, exhibits evidence for an infrared zero. As part of our analysis, we calculate and analyze Padé approximants to this beta function and evaluate effects of scheme dependence. From our study, we find that in the range of coupling where the perturbative calculation of the four-loop beta function is reliable, it does not exhibit robust evidence for an infrared zero.

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arXiv2016

An Integral Formalism for the Construction of Scheme Transformations in Quantum Field Theory

We present an integral formalism for constructing scheme transformations in a quantum field theory. We apply this to generate several new useful scheme transformations. A comparative analysis is given of these scheme transformations in terms of their series expansion coefficients and their resultant effect on the interaction coupling, in particular at a zero of the beta function away from the origin in coupling-constant space.

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arXiv2016

Study of the Renormalization-Group Evolution of ${\cal N}=1$ Supersymmetric Gauge Theories Using Padé Approximants

We study asymptotically free SU($N_c$) gauge theories with ${\cal N}=1$ supersymmetry, including the purely gluonic theory and theories with $N_f$ copies of a pair of massless chiral superfields in the respective representations $R$ and $\bar R$ of SU($N_c$). The cases in which $R$ is the fundamental representation and the symmetric and antisymmetric rank-2 tensor representation are considered. We calculate Padé approximants to the beta functions for these theories in the $\overline{\rm DR}$ scheme up to four-loop order for the gluonic theory and up to three-loop order for the theories with matter superfields and compare results for IR zeros and poles with results from the NSVZ beta function. Our calculations provide a quantitative measure, for these theories, of how well finite-order perturbative results calculated in one scheme reproduce properties of a known beta function calculated in a different scheme.

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arXiv2014

New Scheme Transformations and Application to Study Scheme Dependence of an Infrared Zero of the Beta Function in Gauge Theories

We present two new one-parameter families of scheme transformations and apply these to study the scheme dependence of the infrared zero in the beta function of an asymptotically free non-Abelian gauge theory up to four-loop order. Our results provide a further quantitative measure of this scheme dependence, showing that for moderate values of the gauge coupling and the parameter specifying the scheme transformation, this dependence is relatively mild. We also remark on a generalized multi-parameter family of rational scheme transformations.

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