No axions in light shinning through a wall experiments

Axionic domain wall number related to U(1)$_{\rm anom}$ global symmetry

The QCD axion with $f_a$ at an intermediate scale, 10**9-10**12 GeV, seems in conflict with the gravity spoil of global symmetries and may face the axionic domain wall problem. We point out that the string compactifications with an anomalous U(1) gauge symmetry, allowing desirable chiral matter spectra, circumvent these two problems simultaneously.

Note on a solution to domain wall problem with the Lazarides-Shafi mechanism in axion dark matter models

Axion is a promising candidate of dark matter. After the Peccei-Quinn symmetry breaking, axion strings are formed and attached by domain walls when the temperature of the universe becomes comparable to the QCD scale. Such objects can cause cosmological disasters if they are long-lived. As a solution for it, the Lazarides-Shafi mechanism is often discussed through introduction of a new non-Abelian (gauge) symmetry. We study this mechanism in detail and show configuration of strings and walls. Even if Abelian axion strings with a domain wall number greater than one are formed in the early univer…

Deconfinement on axion domain walls

We study $SU(N_c)$ gauge theories with Dirac fermions in representations ${\cal{R}}$ of nonzero $N$-ality, coupled to axions. These theories have an exact discrete chiral symmetry, which has a mixed 't Hooft anomaly with general baryon-color-flavor backgrounds, called the "BCF anomaly" in arXiv:1909.09027. The infrared theory also has an emergent $\mathbb Z_{N_c}^{(1)}$ $1$-form center symmetry. We show that the BCF anomaly is matched in the infrared by axion domain walls. We argue that $\mathbb Z_{N_c}^{(1)}$ is spontaneously broken on axion domain walls, so that nonzero $N$-ality Wilson loop…

Axion domain wall baryogenesis

We propose a new scenario of baryogenesis, in which annihilation of axion domain walls generates a sizable baryon asymmetry. Successful baryogenesis is possible for a wide range of the axion mass and decay constant, $m \simeq 10^8 -10^{13}$ GeV and $f \simeq 10^{13} - 10^{16}$ GeV. Baryonic isocurvature perturbations are significantly suppressed in our model, in contrast to various spontaneous baryogenesis scenarios in the slow-roll regime. In particular, the axion domain wall baryogenesis is consistent with high-scale inflation which generates a large tensor-to-scalar ratio within the reach o…

有和没有隐藏轴子情况下QCD夸克凝聚体的宇宙弦与畴壁

Cosmic strings and domain walls of the QCD quark condensate with and without a hidden axion

本文研究QCD夸克凝聚体形成的轴子型弦-壁系统，指出其独立于隐藏轴子存在并可能主导早期宇宙演化，同时分析了费米子零模、反常流入及其在QCD相变和重离子物理中的意义。

Domain Wall Formation from Level Crossing in the Axiverse

We point out that domain wall formation is a more common phenomenon in the Axiverse than previously thought. Level crossing could take place if there is a mixing between axions, and if some of the axions acquire a non-zero mass through non-perturbative effects as the corresponding gauge interactions become strong. The axion potential changes significantly during the level crossing, which affects the axion dynamics in various ways. We find that, if there is a mild hierarchy in the decay constants, the axion starts to run along the valley of the potential, passing through many crests and troughs…

无质量费米子与弦-墙复合体的超导性

Massless fermions and superconductivity of string-wall composites

本文研究弦-墙复合体上无质量费米子的存在性与局域位置，通过求解狄拉克方程给出解析零模解，并证明其超导性及反常电流。

带计时器的偏置：轴子畴壁衰变与暗物质

Bias with a Timer: Axion Domain Wall Decay and Dark Matter

该研究探讨暴胀后QCD轴子与轻标量场的相互作用，通过弦-畴壁网络衰变等机制产生轴子暗物质，在无精细调谐下实现正确丰度。

厚轴子畴壁上手征电磁波的局域化

Localization of Chiral Electromagnetic Waves on Thick Axion Domain Walls

研究轴子畴壁与麦克斯韦理论的耦合，发现有限宽度畴壁支持具有线性无能散色散的局域手征电磁模式，该模式源于轴子梯度引起的螺旋度依赖耦合。

Level Crossing between QCD Axion and Axion-Like Particle

We study a level crossing between the QCD axion and an axion-like particle, focusing on the recently found phenomenon, the axion roulette, where the axion-like particle runs along the potential, passing through many crests and troughs, until it gets trapped in one of the potential minima. We perform detailed numerical calculations to determine the parameter space where the axion roulette takes place, and as a result domain walls are likely formed. The domain wall network without cosmic strings is practically stable, and it is nothing but a cosmological disaster. In a certain case, one can make…

Cosmological Perturbations of Axion with a Dynamical Decay Constant

A QCD axion with a time-dependent decay constant has been known to be able to accommodate high-scale inflation without producing topological defects or too large isocurvature perturbations on CMB scales. We point out that a dynamical decay constant also has the effect of enhancing the small-scale axion isocurvature perturbations. The enhanced axion perturbations can even exceed the periodicity of the axion potential, and thus lead to the formation of axionic domain walls. Unlike the well-studied axionic walls, the walls produced from the enhanced perturbations are not bounded by cosmic strings…

轴子与畴壁和泡壁的相互作用

Axion Interactions with Domain and Bubble Walls

本研究发现类轴子粒子与相变泡壁、畴壁等一维余维缺陷的相互作用会产生与洛伦兹因子平方成正比的摩擦力，可改变早期宇宙壁的演化及引力波特征，还会生成超相对论性轴子壳暗辐射。

Axion-Dilaton Domain Walls and Fake Supergravity

Dynamical systems methods are used to investigate domain-wall solutions of a two-parameter family of models in which gravity is coupled to an axion, and to a dilaton with an exponential potential of either sign. A complete global analysis is presented for (i) constant axion and (ii) flat walls, including a study of bifurcations and a new exact domain-wall solution with non-constant axion. We reconsider `fake supergravity' issues in light of these results. We show, by example, how domain walls determine multi-valued superpotentials that branch at stationary points that are not stationary points…

暴胀后 QCD 轴子的质量/宇宙学张力

The Quality/Cosmology Tension for a Post-Inflation QCD Axion

本文指出暴胀后 QCD 轴子模型在解决轴子质量问题时易引发宇宙学畴壁、分数电荷遗迹等灾难，两者存在张力，使得构建可行模型远比预期困难。

高再加热温度而不产生轴子域壁

High Reheating Temperature without Axion Domain Walls

该研究提出了一种无需轴子域壁的PQ对称性打破机制，通过高温度下的标量相互作用实现，解决了等 curvature问题并允许高再加热温度。

轴子电动力学中拓扑孤子的选择规则：来自非可逆对称性

Selection rules of topological solitons from non-invertible symmetries in axion electrodynamics

该研究探讨了轴子电动力学中非可逆对称性如何决定拓扑孤子（如轴子畴壁和磁弦）的选择规则，并给出了磁单极子存在下的约束，以及磁弦与轴子弦链接构型的新限制。

Chern-Simons引力中源于轴子畴壁的圆偏振引力波

Circularly polarized gravitational waves in Chern-Simons gravity originated from an axion domain wall

本文研究Chern-Simons引力中轴子畴壁对引力波的散射，发现穿过畴壁后会产生显著的圆偏振，其强度取决于引力波频率与由CS长度尺度和畴壁能量尺度决定的临界值的关系，从而为约束CS长度尺度或寻找轴子提供新途径。

轴子域墙因螺旋原始磁场而崩溃

Collapse of Axion Domain Wall Induced by Helical Primordial Magnetic Fields

本研究通过Chern-Simons项将轴子场与螺旋原始磁场耦合，发现该磁场的关联长度影响域墙衰变及引力波辐射。

Cosmic String in Abelian-Higgs Model with Enhanced Symmetry -- Implication to the Axion Domain-Wall Problem --

In our previous work, we found new types of the cosmic string solutions in the Abelian-Higgs model with an enhanced $U(1)$ global symmetry. We dubbed those solutions as the compensated/uncompensated strings. The compensated string is similar to the conventional cosmic string in the Abrikosov-Nielsen-Olesen (ANO) string, around which only the would-be Nambu-Goldstone (NG) boson winds. Around the uncompensated string, on the other hand, the physical NG boson also winds, where the physical NG boson is associated with the spontaneous breaking of the enhanced symmetry. Our previous simulation in th…

特殊乘积大统一理论中的小瞬子与暴胀后的QCD轴子

Small Instantons and the Post-Inflationary QCD Axion in a Special Product GUT

提出一种基于特殊乘积GUT的新框架，通过小瞬子效应解决暴胀后PQ对称性破缺导致的畴壁问题，并给出不同于普通模型的暗物质轴子窗口预测。

非紧致QCD轴子

A non-compact QCD axion

非紧致QCD轴子通过产生域墙并引发引力波背景，解释暗物质并规避传统宇宙学约束。

轴子电动力学：格林函数、零点能与光学活性

Axion electrodynamics: Green's functions, zero-point energy and optical activity

本文利用格林函数方法研究了轴子电动力学中时间依赖轴子场和静态畴壁对卡西米尔能量及辐射压强的修正，并将结果推广到有限温度，同时讨论了其在拓扑绝缘体和光学活性中的应用。

Novel Physics with International Pulsar Timing Array: Axionlike Particles, Domain Walls and Cosmic Strings

After NANOGrav, the IPTA collaboration also reports a strong evidence of a stochastic gravitation wave background. This hint has very important implications for fundamental physics. With the recent IPTA data release two, we attempt to search signals of light new physics. and give new constraints on the audible axion, domain walls and cosmic strings models. We find that the best fit point corresponding to a decay constant $F\approx5\times10^{17}$ GeV and an axion mass $m_a\approx2\times10^{-13}$ eV from NANOGrav data is ruled out by IPTA at beyond $2σ$ confidence level. Fixing the coupling stre…

Lazarides-Shafi 轴子模型作为 Dijkgraaf-Witten 理论

Lazarides-Shafi axion models as Dijkgraaf-Witten theories

Lazarides-Shafi 轴子模型通过连续规范对称性解决墙问题，并利用拓扑量子场论分析其更高形式对称性结构，提出计算墙数的主公式及SPT相的实现。

Looking at the NANOGrav Signal Through the Anthropic Window of Axion-Like Particles

We explore the inflationary dynamics leading to formation of closed domain walls in course of evolution of an axion like particle (ALP) field whose Peccei-Quinn-like phase transition occurred well before inflationary epoch. Evolving after inflation, the domain walls may leave their imprint in stochastic gravitational waves background, in the frequency range accessible for the pulsar timing array measurements. We derive the characteristic strain power spectrum produced by the distribution of the closed domain walls and relate it with the recently reported NANOGrav signal excess. We found that t…

轴子畴壁上由 Chern-Simons 诱导的热摩擦

Chern-Simons Induced Thermal Friction on Axion Domain Walls

本文利用线性响应方法研究了包含 Chern-Simons 相互作用的轴子电动力学模型中畴壁在相对论性热等离子体中受到的热摩擦，纠正了薄壁极限下的以往表达式，并探讨了早期宇宙中相干磁场效应及对畴壁演化、引力波和原初黑洞产生的影响。

Axion Monodromy and the Weak Gravity Conjecture

Axions with broken discrete shift symmetry (axion monodromy) have recently played a central role both in the discussion of inflation and the `relaxion' approach to the hierarchy problem. We suggest a very minimalist way to constrain such models by the weak gravity conjecture for domain walls: While the electric side of the conjecture is always satisfied if the cosine-oscillations of the axion potential are sufficiently small, the magnetic side imposes a cutoff, $Λ^3 \sim m f M_{pl}$, independent of the height of these `wiggles'. We compare our approach with the recent related proposal by Ibane…

Analytic continuations of de Sitter thick domain wall solutions

We perform some analytic continuations of the de Sitter thick domain wall solutions obtained in our previous paper hep-th/0201130 in the system of gravity and a scalar field with an axion-like potential. The obtained new solutions represent anti-de Sitter thick domain walls and cosmology. The anti-de Sitter domain wall solutions are periodic, and correspondingly the cosmological solutions represent cyclic universes. We parameterize the axion-like scalar field potential and determine the parameter regions of each type of solutions.

Late-time entropy production due to the decay of domain walls

It is shown that late-time decay of domain walls can dilute unwanted relics such as moduli, if the universe was dominated by frustrated domain walls with tension $σ= (1 - 100 TeV)^3$. Since energy density of the frustrated domain walls decreases as slow as the inverse of the scale factor, an overclosure limit on the axion decay constant $f_a$ is also considerably relaxed. In fact $f_a$ can be as large as the Planck scale, which may enable us to naturally implement the QCD axion in the string scheme. Furthermore, in contrast to thermal inflation models, the Affleck-Dine baryogenesis can generat…

Inflection-Point Inflation with Axion Dark Matter in light of Trans-Planckian Censorship Conjecture

Motivated by the recently proposed Trans-Planckian Censorship Conjecture (TCC), we propose a gauged $B-L$ model of inflection-point inflation with axion dark matter. The Hubble scale during inflation ($H_{\rm inf}$) satisfies the TCC bound of $H_{\rm inf} \lesssim 1$ GeV, the axion dark matter scenario is free from the axion domain wall and isocurvature problems, and the axion decay constant can be larger than $10^{12}$ GeV. The seesaw mechanism is automatically incorporated in the model and the observed baryon asymmetry of the universe can be reproduced via resonant leptogenesis.

Naturally light invisible axion and local Z_{13} times Z_3 symmetries

We show that by imposing local $Z_{13}\otimes Z_3$ symmetries in an $SU(2)\otimes U(1)$ electroweak model we can implement an invisible axion in such a way that (i) the Peccei-Quinn symmetry is an automatic symmetry of the classical Lagrangian; and (ii) the axion is protected from semi classical gravitational effects. In order to be able to implement such a large discrete symmetry, and at the same time allow a general mixing in each charge sector, we introduce right-handed neutrinos and enlarge the scalar sector of the model. The domain wall problem is briefly considered.

Lunar Mass Black Holes from QCD Axion Cosmology

In the QCD axion scenario, a network of domain walls bounded by cosmic strings fragments into pieces. As these fragments collapse, some of them will form black holes. With standard QCD axion parameters, the black holes will have lunar masses ($M_{\rm bh} \sim 10^{-8}\, {\rm M}_\odot$). Even though their number density is difficult to estimate, arguments suggest that they can constitute a reasonable fraction of the critical cosmological density.

Emergent discrete 3-form symmetry and domain walls

We show that axion models with the domain wall number $k$ in $(3+1)$ dimensions, i.e., periodic scalar field theories admitting $k$ axion domain walls, exhibit an emergent ${\mathbb Z}_k$ 3-form symmetry for $k >1$ in addition to a conventional ${\mathbb Z}_k$ 0-form symmetry. The emergent 3-form symmetry is explicitly shown by establishing a low-energy dual transformation between the scalar field theory and a 3-form gauge theory. We further argue that the emergent 3-form symmetry is spontaneously broken, and the breaking pattern is so-called the type-B spontaneous symmetry breaking. We discus…

Entropy of charged dilaton-axion black hole

Using brick wall method the entropy of charged dilaton-axion black hole is determined for both asymptotically flat and non-flat cases. The entropy turns out to be proportional to the horizon area of the black hole confirming the Beckenstien, Hawking area-entropy formula for black holes. The leading order logarithmic corrections to the entropy are also derived for such black holes.

拓扑绝缘半空间上方短线性天线的辐射

Radiation of a short linear antenna above a topologically insulating half-space

本文采用 Green 函数方法求解含平面拓扑畴壁的轴子电动力学含时场方程，并据此分析三维拓扑绝缘体附近短线性天线的辐射特性。