arXiv subjects

Y. H. Ahn

Publications and source records attributed to Y. H. Ahn.

At least 19 recordsLinked to original sources

arXiv2024

Neutrino Mass Origin and Flavored-QCD axion in an Extra-Dimension

We propose a unified flavor model with the Standard Model fields on two 3-branes within an extra-dimensional setup, incorporating $Γ_N\times U(1)_X$ symmetry with a modulus and scalar field responsible for symmetry breaking. When compactified to four dimensions, Yukawa couplings, initially expressed as modular forms with mass dimensions, are normalized to conform to canonical four-dimensional theory, with the Yukawa coefficients being complex numbers of unit absolute value. We show that this model naturally explains the mass and mixing hierarchies of quarks and leptons, solves the strong CP problem, provides a natural solution to the hierarchy problem, and can inherently satisfy no axionic domain-wall problem. The $U(1)_X$ mixed gravitational anomaly-free condition necessitates that electrically neutral mirror bulk fermions couple to the normal neutrino field on the 3-brane, consistent with the boundary condition. Consequently, we demonstrate a mechanism for generating light neutrino masses, similar to the Weinberg operator, by transmitting the information of $U(1)_X$ breakdown between the two 3-branes. The scale of $U(1)_X$ breaking is estimated from neutrino data to be around $10^{15}$ GeV, leading to a QCD axion mass of approximately $2.5\times10^{-9}$ eV. Through numerical analysis, we demonstrate that the model yields results consistent with current experimental data on quarks and leptons, and it also provides predictions for neutrinos.

hep-ph↗

arXiv2023

Simple Modular invariant model for Quark, Lepton, and flavored-QCD axion

We propose a minimal extension of the Standard Model by incorporating sterile neutrinos and a QCD axion to account for the mass and mixing hierarchies of quarks and leptons and to solve the strong CP problem, and by introducing $G_{\rm SM}\times Γ_N\times U(1)_X$ symmetry. We demonstrate that the K{ä}hler transformation corrects the weight of modular forms in the superpotential and show that the model is consistent with the modular and $U(1)_X$ anomaly-free conditions. This enables a simple construction of a modular-independent superpotential for scalar potential. Using minimal supermultiplets, we demonstrate a level 3 modular form-induced superpotential. Sterile neutrinos explain small active neutrino masses via the seesaw mechanism and provide a well-motivated $U(1)_X$ breaking scale, whereas gauge singlet scalar fields play crucial roles in generating the QCD axion, heavy neutrino mass, and fermion mass hierarchy. The model predicts a range for the $U(1)_X$ breaking scale from $10^{13}$ GeV to $10^{15}$ GeV for $1\,\mbox{TeV}< m_{3/2}<10^6\,\mbox{TeV}$. In the supersymmetric limit, all Yukawa coefficients in the superpotential are given by complex numbers with an absolute value of unity, implying a democratic distribution. Performing numerical analysis, we study how model parameters are constrained by current experimental results. In particular, the model predicts that the value of the quark Dirac CP phase falls between $38^\circ$ to $87^\circ$, which is consistent with experimental data, and the favored value of the neutrino Dirac CP phase is around $250^\circ$. Furthermore, the model can be tested by ongoing and future experiments on axion searches, neutrino oscillations, and $0νββ$-decay.

hep-ph↗

arXiv2021

Towards a Model of Quarks and Leptons

We propose an extra-dimension framework on the orbifold $S^1/Z_2$ for understanding the origin of the fermion mass and mixing hierarchies. Introducing the flavor symmetry $G_F(=${\it non-Abelian}$\times${\it Abelian}) as well as the extra gauged $U(1)$ symmetries through the bulk, we regard the $SU(2)$ singlet and doublet fermions in the Standard Model (SM) to be localized at the separate 3-branes and let the extra $SU(2)$ singlet flavored fermions in the bulk couple to the SM fermions at the 3-branes. The extra $U(1)$ symmetries satisfy the $U(1)$ gravitational anomaly-free condition, playing a crucial role in achieving the desirable fermion mass and mixing hierarchies and making the flavored axion naturally light. The singlet scalar fields, the flavon fields, are responsible for the spontaneous breaking of $G_F$ on the two 3-branes, while the $SU(2)$ singlet flavored fermions are integrated out to give rise to the effective Yukawa couplings for the SM fermions, endowed with the information of $G_F$ breaking in the two sectors. The flavored axion from the PQ symmetry is also proposed for solving the strong CP problem and being a dark matter candidate in our model.

hep-ph↗

arXiv2021

Challenge to Anomalous Phenomena in Solar Neutrino

We suggest a would-be solution to the solar neutrino tension why solar neutrinos appear to mix differently from reactor antineutrinos, in theoretical respect. To do that, based on an extended theory with light sterile neutrinos added we derive a general transition probability of neutrinos born with one flavor tuning into a different flavor. Three new mass-squared differences are augmented in the extended theory: two $Δm^2_{\rm ABL}\lesssim{\cal O}(10^{-11})\,{\rm eV}^2$ optimized at astronomical-scale baseline (ABL) oscillation experiments and one $Δm^2_{\rm SBL}\sim{\cal O}(1)\,{\rm eV}^2$ optimized at reactor short-baseline (SBL) oscillation experiments. With a so-called composite matter effect that causes a neutrino flavor change via the effects of sinusoidal oscillation including the Mikheyev-Smirnov-Wolfenstein matter effect, we find that the value of $Δm^2$ measured from reactor antineutrino experiments can be fitted with that from the $^8$B solar neutrino experiments for roughly $Δm^2_1\lesssim10^{-13}\,{\rm eV}^2$ and $Δm^2_2\simeq{\cal O}(10^{-11})\,{\rm eV}^2$. Nonetheless, we find that the current data (solar neutrino alone) is not precise enough to test the proposed scenario. Future precise measurements of $^8$B and $pep$ solar neutrinos may confirm and/or improve the value of $Δ{m}^2_2$.

hep-ph↗

arXiv2020

QCD axion and Neutrino induced by Hidden flavor structure

We study the reasonable requirements of two anomalous $U(1)$s in a flavored-axion framework for the anomaly cancellations of both $U(1)$-mixed gravity and $U(1)_Y\times[U(1)]^2$ which in turn determine the $U(1)_Y$ charges where $U(1)_Y$ is the hypercharge gauge symmetry of the standard model. We argue that, with a flavor symmetry group, axion-induced topology in symmetry-broken phases plays crucial roles in describing how quarks and leptons are organized at a fundamental level and make deep connections with each other. A unified model, as an example, is then proposed in a simple way to describe a whole spectrum of particles where both flavored-axion interactions with normal matter and the masses and mixings of fermions emerge from the spontaneous breaking of a given symmetry group. Once a scale of active neutrino mass defined at a seesaw scale is fixed by the commensurate $U(1)$ flavored-PQ charge of fermions, that of QCD axion decay constant $F_A$ is determined. In turn, fundamental physical parameters complementary to each other are predicted with the help of precision flavor experiments. Model predictions are extracted on the characteristics of neutrino and flavored-axion: $F_A=3.57^{\,+1.52}_{\,-1.53}\times10^{10}$ GeV (consequently, QCD axion mass $m_a=1.52^{+1.14}_{-0.46}\times10^{-4}$ eV, axion to photon coupling $|g_{aγγ}|=2.15^{+1.61}_{-0.64}\times10^{-14}\,\text{GeV}^{-1}$, axion to electron coupling $g_{Aee}=3.29^{+2.47}_{-0.98}\times10^{-14}$, etc.); atmospheric mixing angle $θ_{23}$, Dirac CP phase $δ_{CP}$, and $0νββ${\it-decay rate} for normal mass ordering and inverted one by taking quantum corrections into account.

hep-ph↗

arXiv2019

A Model of Neutrino Anomalies and IceCube data

We interpret the neutrino anomalies in neutrino oscillation experiments and the high energy neutrino events at IceCube in terms of neutrino oscillations in an extension of the standard model where three sterile neutrinos are introduced so as to make two light neutrinos to be Pseudo-Dirac particles and a light neutrino to be a Majorana particle. Our model is different from the so-called $3+n$ model with $n$ sterile neutrinos suggested to interpret short baseline anomalies in terms of neutrino oscillations. While the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix in $3+n$ model is simply extended to $n\times n$ unitary matrix, the neutrino mixing matrix in our model is parameterized so as to keep the $3\times3$ PMNS mixing matrix for three active neutrinos unitary. There are also no flavor changing neutral current interactions leading to the conversion of active neutrinos to sterile ones or vice versa. We derive new forms of neutrino oscillation probabilities containing the new interference between the active and sterile neutrinos which are characterized by additional new parameters $Δm^2$ and $θ$. Based on the new formulae derived, we show how the short baseline neutrino anomalies can be explained in terms of oscillations, and study the implication of the high energy neutrino events detected at IceCube on the probe of pseudo-Dirac neutrinos. New phenomenological effects attributed to the existence of the sterile neutrinos are discussed.

hep-ph↗

arXiv2019

Strain-engineering of Berry curvature dipole and valley magnetization in monolayer MoS$_2$

The Berry curvature dipole is a physical quantity that is expected to allow various quantum geometrical phenomena in a range of solid-state systems. Monolayer transition metal dichalcogenides provide an exceptional platform to modulate and investigate the Berry curvature dipole through strain. Here we theoretically demonstrate and experimentally verify for monolayer MoS$_\rm{2}$ the generation of valley orbital magnetization as a response to an in-plane electric field due to the Berry curvature dipole. The measured valley orbital magnetization shows excellent agreement with the calculated Berry curvature dipole which can be controlled by the magnitude and direction of strain. Our results show that the Berry curvature dipole acts as an effective magnetic field in current-carrying systems, providing a novel route to generate magnetization.

cond-mat.mes-hall↗

arXiv2019

Inflation and Leptogenesis in a $U(1)$-enhanced supersymmetric model

Motivated by the flavored Peccei-Quinn symmetry for unifying flavor physics and string theory, we investigate a supersymmetric extension of standard model (SM) for an explanation of inflation and leptogenesis by introducing $U(1)$ symmetries such that the $U(1)$-$[gravity]^2$ anomaly-free condition together with the SM flavor structure demands additional sterile neutrinos as well as no axionic domain-wall problem. Such additional neutrinos may play a crucial role as a bridge between leptogenesis and new neutrino oscillations along with high energy cosmic events. In a realistic moduli stabilization, we show that the moduli backreaction effect on the inflationary potential leads to the energy scale of inflation with the inflaton mass in a way that the power spectrum of the curvature perturbation and the scalar spectral index are to be well fitted with the latest Planck observation. We suggest that a new leptogenesis scenario could naturally be implemented via Affleck-Dine mechanism. So we show that the resultant baryon asymmetry, constrained by the sum of active neutrino masses and new high energy neutrino oscillations, crucially depends on the reheating temperature $T_{\rm reh}$. And we show that the model has a preference on $T_{\rm reh}\sim10^3$ TeV, which is compatible with the required $T_{\rm reh}$ to explain the baryon asymmetry of the Universe.

hep-ph↗

arXiv2019

Fermion masses and flavor mixings and strong CP problem

For all the success of the Standard Model (SM), it is on the verge of being surpassed. In this regard we argue, by showing a minimal flavor-structured model based on the non-Abelian discrete $SL_2(F_3)$ symmetry, that $U(1)$ mixed-gravitational anomaly cancellation could be of central importance in constraining the fermion contents of a new chiral gauge theory. Such anomaly-free condition together with the SM flavor structure demands a condition $k_1\,X_1/2=k_2\,X_2$ with $X_i$ being a charge of $U(1)_{X_i}$ and $k_i$ being an integer, both of which are flavor dependent. We show that axionic domain-wall condition $N_{\rm DW}$ with the anomaly free-condition depends on both $U(1)_X$ charged quark and lepton flavors; the seesaw scale congruent to the scale of Peccei-Quinn symmetry breakdown can be constrained through constraints coming from astrophysics and particle physics. Then the model extended by $SL_2(F_3)\times U(1)_X$ symmetry can well be flavor-structured in a unique way that $N_{\rm DW}=1$ with the $U(1)_X$ mixed-gravitational anomaly-free condition demands additional Majorana fermion and the flavor puzzles of SM are well delineated by new expansion parameters expressed in terms of $U(1)_X$ charges and $U(1)_X$-$[SU(3)_C]^2$ anomaly coefficients. And the model provides remarkable results on neutrino (hierarchical mass spectra and unmeasurable neutrinoless-double-beta decay rate together with the predictions on atmospheric mixing angle and leptonic Dirac CP phase favored by the recent long-baseline neutrino experiments), QCD axion, and flavored-axion.

hep-ph↗

arXiv2018

Compact model for Quarks and Leptons via flavored-Axions

We show how the scales responsible for Peccei-Quinn (PQ), seesaw, and Froggatt and Nielsen (FN) mechanisms can be fixed, by constructing a compact model for resolving rather recent, but fast-growing issues in astro-particle physics, including quark and leptonic mixings and CP violations, high-energy neutrinos, QCD axion, and axion cooling of stars. The model is motivated by the flavored PQ symmetry for unifying the flavor physics and string theory. The QCD axion decay constant congruent to the seesaw scale, through its connection to the astro-particle constraints of both the stellar evolution induced by the flavored-axion bremsstrahlung off electrons $e+Ze\rightarrow Ze+e+A_i$ and the rare flavor-changing decay process induced by the flavored-axion $K^+\rightarrowπ^++A_i$, is shown to be fixed at $F_A=3.56^{+0.84}_{-0.84}\times10^{10}$ GeV (consequently, the QCD axion mass $m_a=1.54^{+0.48}_{-0.29}\times10^{-4}$ eV, Compton wavelength of its oscillation $λ_a=8.04^{+1.90}_{-1.90}\,{\rm mm}$, and axion to neutron coupling $g_{Ann}=2.14^{+0.66}_{-0.41}\times10^{-12}$, etc.). Subsequently, the scale associated to FN mechanism is dynamically fixed through its connection to the standard model fermion masses and mixings, $Λ=2.04^{\,+0.48}_{\,-0.48}\times10^{11}\,{\rm GeV}$, and such fundamental scale might give a hint where some string moduli are stabilized in type-IIB string vacua. In the near future, the NA62 experiment expected to reach the sensitivity of ${\rm Br}(K^+\rightarrowπ^++A_i)<1.0\times10^{-12}$ will probe the flavored-axions or exclude the model, if the astrophysical constraint of star cooling is really responsible for the flavored-axion.

hep-ph↗

arXiv2017

A necessary condition for sphaleron process in the presence of anomalous $U(1)$ symmetry

We argue that, in the presence of anomalous $U(1)$ symmetries, the invariance of Lagrangian including the standard model (SM) under the axionic shift symmetries requires a necessary condition $\sum_iδ^{\rm GS}_{i}\leq2N_f$, where $N_f$ stands for the number of families in the SM and $δ^{\rm GS}_i$ (Green-Schwarz parameter) characterizes the coupling of the anomalous $U(1)$ gauge boson to the corresponding axion. In turn, we show that in order for the usual $B+L$ violating sphaleron process to be valid a necessary condition $\sum_iδ^{\rm GS}_{i}<2N_f$ is required, where $B(L)$ stands for the baryon(lepton) number.

hep-ph↗

arXiv2017

Axion and Neutrino physics in a $U(1)$-enhanced supersymmetric model

Motivated by the flavored Peccei-Quinn symmetry for unifying the flavor physics and string theory, we construct an explicit model by introducing a $U(1)$ symmetry such that the $U(1)_X$-$[gravity]^2$ anomaly-free condition together with the standard model flavor structure demands additional sterile neutrinos as well as no axionic domain-wall problem. Such additional sterile neutrinos play the role of a realization of baryogenesis via a new Affleck-Dine leptogenesis. We provide grounds for that the $U(1)_X$ symmetry could be interpreted as a fundamental symmetry of nature. The model will resolve rather recent, but fast-growing issues in astro-particle physics, including leptonic mixings and CP violation in neutrino oscillation, high-energy neutrinos, QCD axion, and axion cooling of stars. The QCD axion decay constant, through its connection to the astrophysical constraints of stellar evolution and the SM fermion masses, is shown to be fixed at $F_A=1.30^{+0.66}_{-0.54}\times10^{9}$ GeV (consequently, its mass is $m_a=4.34^{+3.37}_{-1.49}$ meV and axion-photon coupling is $|g_{aγγ}|=1.30^{+1.01}_{-0.45}\times10^{-12}\,{\rm GeV}^{-1}$). Interestingly enough, we show that neutrino oscillations at low energies could be connected to astronomical-scale baseline neutrino oscillations. The model predicts non-observational neutrinoless double beta ($0νββ$) decay rate as well as a remarkable pattern between leptonic Dirac CP phase ($δ_{CP}$) and atmospheric mixing angle ($θ_{23}$); {\it e.g.} $δ_{CP}\simeq220^{\circ}-240^{\circ}$, $120^{\circ}-140^{\circ}$ for $θ_{23}=42.3^{\circ}$ for normal mass ordering, and $δ_{CP}\simeq283^{\circ},250^{\circ},100^{\circ},70^{\circ}$ for $θ_{23}=49.5^{\circ}$ for inverted one.

hep-ph↗

arXiv2016

A Model for Pseudo-Dirac Neutrinos: Leptogenesis and Ultra-High Energy Neutrinos

We propose a model where sterile neutrinos are introduced to make light neutrinos to be pseudo-Dirac particles. It is shown how tiny mass splitting necessary for realizing pseudo-Dirac neutrinos can be achieved. Within the model, we show how leptogenesis can be successfully generated. Motivated by the recent observation of very high energy neutrino events at IceCube, we study a possibility to observe the effects of the pseudo-Dirac property of neutrinos by performing astronomical-scale baseline experiments to uncover the oscillation effects of very tiny mass splitting. Using the result of global fit to neutrino data for the input of neutrino mixing angles and CP phase at $1σ$ C.L. and fixing neutrino energy and mass splittings, we study how the oscillation effects induced by pseudo-Dirac neutrinos may affect the track-to-shower ratio obtained from IceCube data. We also discuss future prospect to observe the effects of the pseudo-Dirac property of neutrinos at high energy neutrino experiments.

hep-ph↗

arXiv2016

QCD Axion as a Bridge Between String Theory and Flavor Physics

We construct a string-inspired model, motivated by the flavored Peccei-Quinn (PQ) axions, as a useful bridge between flavor physics and string theory. The key feature is two anomalous gauged $U(1)$ symmetries, responsible for both the fermion mass hierarchy problem of the standard model and the strong CP problem, that combine string theory with flavor physics and severely constrain the form of the F- and D-term contributions to the potential. In the context of supersymmetric moduli stabilization we stabilize the size moduli with positive masses while leaving two axions massless and one axion massive. We demonstrate that, while the massive gauge bosons eat the two axionic degrees of freedom, two axionic directions survive to low energies as the flavored PQ axions.

hep-ph↗

arXiv2015

Minimal Models for Axion and Neutrino

The PQ mechanism resolving the strong CP problem and the seesaw mechanism explaining the smallness of neutrino masses may be related in a way that the PQ symmetry breaking scale and the seesaw scale arise from a common origin. Depending on how the PQ symmetry and the seesaw mechanism are realized, one has different predictions on the color and electromagnetic anomalies which could be tested in the future axion dark matter search experiments. Motivated by this, we construct various PQ seesaw models which are minimally extended from the (non-) supersymmetric Standard Model and thus set up different benchmark points on the axion-photon-photon coupling in comparison with the standard KSVZ and DFSZ models.

hep-ph↗

arXiv2015

Flavored Peccei-Quinn symmetry

In an attempt to uncover any underlying physics in the standard model (SM), we suggest a $μ$--$τ$ power law in the lepton sector, such that relatively large 13 mixing angle with bi-large ones can be derived. On the basis of this, we propose a neat and economical model for both the fermion mass hierarchy problem of the SM and a solution to the strong CP problem, in a way that no domain wall problem occurs, based on $A_{4}\times U(1)_{X}$ symmetry in a supersymmetric framework. Here we refer to the global $U(1)_X$ symmetry that can explain the above problems as "flavored Peccei-Quinn symmetry". In the model, a direct coupling of the SM gauge singlet flavon fields responsible for spontaneous symmetry breaking to ordinary quarks and leptons, both of which are charged under $U(1)_X$, comes to pass through Yukawa interactions, and all vacuum expectation values breaking the symmetries are connected each other. So, the scale of Peccei-Quinn symmetry breaking is shown to be roughly located around $10^{12}$ GeV section through its connection to the fermion masses. The model predictions are shown to lie on the testable regions in the very near future through on-going experiments for neutrino oscillation, neutrinoless double beta decay and axion. We examine the model predictions, arisen from the $μ$--$τ$ power law, on leptonic $CP$ violation, neutrinoless double beta decay and atmospheric mixing angle, and show that the fermion mass and mixing hierarchies are in good agreement with the present data. Interestingly, we show the model predictions on the axion mass $m_a\simeq2.53\times10^{-5}$ eV and the axion coupling to photon $g_{aγγ}\simeq1.33\times10^{-15}~{\rm GeV}^{-1}$. And subsequently the square of the ratio between them is shown to be 1 or 2 orders of magnitude lower than that of the conventional axion model.

hep-ph↗

arXiv2014

Towards a realistic model of quarks and leptons, leptonic CP violation and neutrinoless $ββ$-decay

In order to explain the fermion masses and mixings naturally, we introduce a specific flavor symmetry and mass suppression pattern that constrain the flavor structure of the fermion Yukawa couplings. Our model describes why the hierarchy of neutrino masses is milder than the hierarchy of charged fermion masses in terms of successive powers of flavon fields. We investigate CP violation and neutrinoless double beta ($0νββ$) decay, and show how they can be predicted and constrained in our model by present and upcoming experimental data. Our model predicts that the atmospheric neutrino mixing angle $θ_{23}$ should be within $\sim1^{\circ}$ of $45^\circ$ for the normal neutrino mass ordering (NO), and between $\sim4^\circ$ and $\sim8^\circ$ degrees away from $45^\circ$ (in either direction) for the inverted neutrino mass ordering (IO). For both NO and IO, our model predicts that a $0νββ$ Majorana mass in the limited range $0.035 \text{eV}<|m_{ee}|\lesssim0.15$ eV, which can be tested in current experiments. Moreover, our model can successfully accommodate flavorless leptogenesis as the mechanism to generate the baryon asymmetry in the Universe, provided the neutrino mass ordering is normal, $|m_{ee}|\simeq0.072\pm0.012$ eV, and either $θ_{23}\simeq44^{\circ}$ and the Dirac CP-violating phase $δ_{CP}\simeq20^{\circ}$ or $60^{\circ}$, or $θ_{23}\simeq46^{\circ}$ and $δ_{CP} \simeq205^{\circ}$ or $245^{\circ}$.

hep-ph↗

arXiv2014

Imaging ultrafast carrier transport in nanoscale devices using femtosecond photocurrent microscopy

One-dimensional nanoscale devices, such as semiconductor nanowires (NWs) and single- walled carbon nanotubes (SWNTs), have been intensively investigated because of their potential application of future high-speed electronic, optoelectronic, and sensing devices. To overcome current limitations on the speed of contemporary devices, investigation of charge carrier dynamics with an ultrashort time scale is one of the primary steps necessary for developing high-speed devices. In the present study, we visualize ultrafast carrier dynamics in nanoscale devices using a combination of scanning photocurrent microscopy and time- resolved pump-probe techniques. We investigate transit times of carriers that are generated near one metallic electrode and subsequently transported toward the opposite electrode based on drift and diffusion motions. Carrier dynamics have been measured for various working conditions. In particular, the carrier velocities extracted from transit times increase for a larger negative gate bias, because of the increased field strength at the Schottky barrier.

physics.ins-det↗