Hello World!
目录 一、工作 1. 无情的事实 2. 研究 3. 角色转换 二、生活 1. 作为母亲 2. 作为妻女 3. 作为朋友和自己 三、其他感想 1. 钱财 2. 海内与海外 3. 结尾必然要盲目乐观
Popular posts from this blog
I decide to begin writing some back-of-the-envelope stuff in this blog; mostly very basic things. Consider Dirac fermion coupled to $U(1)$ field. $$\mathcal{L}=\bar{\psi}\gamma^\mu (\partial_\mu-iA_\mu) \psi - \frac{1}{e^2} F_{\mu\nu}F^{\mu\nu}. $$ In d spacetime dimensions, the first part in the kinetic term implies $[\partial]+2[\psi]=d$, leading to $[\psi]=(d-1)/2$. The second part leads to $2[\psi]+[A]=d$. Plugging in the value for $[\psi]$, we have $[A]=1$, then $[F]=2$. Using this and plug back in the Maxwell term $2[F]-[e^2]=d$, we arrive at $[e^2]=4-d$. When we are in 3+1d, the gauge coupling is thus dimensionless. For 2+1d, the gauge coupling has dimension $[e^2]=1$, so this theory is strongly coupled in the infrared. Also, the potential energy between two charges increases logarithmically with respect to the distance between them, which is a very mild form of confinement. References: [1] David Tong, Lectures on gauge theory, chapter 8. http://www.damtp.cam.ac.uk/use...
- Get link
- X
- Other Apps
昨天决定每月少吃一顿外卖，每月给印度一个五岁的小姑娘打三十块钱。原本只是在慈善机构网站上随便浏览，没有打算掏钱，可是选了年龄性别和出生月份以后，那个小姑娘的照片就出现在第一页第一条。她留着利落短发，穿黑色T恤，挂一条骨头做的项链，嘴巴紧抿，眼神倔强。我心头一跳，呆了片刻，关了窗口，又去看网页的其他部分，然后推了一会儿式子。可我总也忘不掉那小姑娘的神情，于是重新打开网页，认命地选了定期资助。网站叫save the children，还可以给小朋友通信。希望能帮到她。 所谓眼缘不过如此。当时我买车也是买了去的第一家店看的第一辆车。七年前第一次和搭档见面，听他打招呼我就心头一跳。其他例子也不少。
- Get link
- X
- Other Apps
Comments
Post a Comment