杂记

一个人想法的多少难道是随着他的知识增长成U型变化趋势的吗？以前只知道皮毛的时候想法很多很大胆，跟民科一样，现在目不暇接地学了一堆东东却似乎什么都不敢想了，因为每一个想法似乎不是有人做过就是马上会被否定掉，经历了太多这样的情况就开始变得麻木了。真是有些担心，不知道学通之后真正有用的想法能不能多起来。就算做model builder, 我的目标也是总工程师。

今年的诺贝尔奖跟我正在关心的东西关系不小，如果有时间我会自己总结一个review,关于对称性自发破缺和费米子混合问题。

美国的高能实验快进入冬天了。美国政府的科研经费申请政策太弱智了，一个大型项目每年都要重新审批，砸了无数钱建到一半都能扔下，不想出钱又狂浪费钱，目光短浅的严重表现。现在好了，金融危机一闹彻底没戏了。

LHC最早在明年4月就能出第一批数据了，而额外维的引力子貌似是需要数据最少的。RS首当其冲啊，要死的话就是死得最早的。这样也好，省得我在上面白白浪费青春。

Some lessons

It’s not easy to start research. The first step is to get use to your advisor and learn many many lessons.

My advisor asks me to calculate a flavor model in the simplest case. It seems that what I am calculating always goes away from what he is thinking, and when I come back to look for his help after wasting a lot of time, he seems already know the answer to the next step. It’s so clear to him what will happen next, but I have to spend many time and energy on it before I see the simple point. I believe he would not even bother to talk with me on these problems if he was not training me. This is the distance between a sophisticated professor and a beginner, he have much more intuition, both mathematically and physically, that is, he can easily guess the result without any complicated calculation. I can’t, I lack the intuition and spent much time on meaningless calculations, I used too many parameters which I do not know how to simplify and have to use mathematica, and of course, no meaningful things came out. He told me not to use mathematica at this time, approximation is much more powerful than exact calculation for the first step of a model. He is right, I should think much before I calculate. I did find a much simpler way to calculate after all, although the setup was too simple to be right.

I find myself doing something I disgusted in my college – model building. I don’t want to become a professional model builder, although my advisor is, and he is really a successful one. In fact he gave me two directions to choose in the beginning, one is more formalistic, something on RS and string theory. I considered that one and gave up, although it’s somewhat closer to me early dream, because he is not a string theorist and string is not a good start point for me. I chose model building for a good chance to learn LHC related phenomenology and more about SM and beyond, but my long goal is not sticked on it. So I should keep in mind: I am not building model, but doing physics; I am not playing toys, but playing with the real world. I should try my best to find the more fundamental physical meaning for what I am doing. I think my advisor is trying to do this. He is not a pure model builder, at least, he is more like an engineer than a worker if we compare model building to house building. But now, I have to start as a worker – do what he tells me to do with the tools he provide to me. I have to make a change, as someone said, good graduate students can lead their advisor in the end.

XD ppt

This is my presentation in the 2nd year seminar, a brief introduction to extra dimensions, which lasted 25 minutes. See here.

进展

其实找到老板不算什么进展，只是终于可以有一个比较确定的方向和稳定的压力让我走下去了。当然，这也意味着我不能随心所欲地想看什么就看什么了，不过失去自由，同时摆脱盲目，也是好事。这一年来，浪费了太多时间在杂事上，又缺乏压力，几乎就停滞不前了。最近两位在pku的好友都陆续发文（here&here)，衷心祝贺他们，同时我也感到了很大的差距。当然发文早晚并不重要，何况这边的培养期普遍都比国内长，一般第二年才有导师，第三年才有课题，不过现在也应该是感到压力的时候了。

像场论和粒子物理这样的东西，只是一味照着书本学确实没有什么效果。曾经好几次发愿要把peskin读完，但都是读一两章又停下来，因为细节太多，看不到大图像，不合我的胃口，还不如跟人讨论学得多。最近在看老板指定的Georgi的Weak Interaction and Particle Physics，比Peskin难，细节也不是很清楚，但写的简洁，整体框架性不错。作为“招生考试”，老板让我做了Georgi书上两道关于轻子Higgs机制的题，尽管题不难，但做得很爽，顿时发现Higgs机制这部分内容清楚了不少。上场论课也做题，都只是一部分的计算，只有数学技能训练，没有物理图像的整理，看来以后要多挑一些这种从头算到尾的问题来练。Peskin和Georgi书上都有这样一些好题。

同级的朋友都发文了，我才刚找到老板，还在做习题玩，实在是有差距啊。不过我也不着急，打好基础是最重要的。像我现在的水平，就算拼出小命做文章，也顶多只是灌水级别的，有什么意义呢？下周老板会跟我商量课题方向，不过他也说了，第一年是不会怎么管的，基本上就是自己看看文章。也好，还有时间系统地学习，但又不像以前那样盲目了，在一个连固定的专业课程都没有破学校，能让老板带着学恐怕是最好的机会了。

POE problems

R: Nuclear Magnetic Resonance. Numerical estimation of the resonant frequency.
R: Ferromagnet. Why are not the spins in one magnetic domain exactly in the same direction? (Something about spin wave)
G: Possible spin J of a particle combined with s=1 and s=0 particles with angular momentum L=1?
Component of J=2, Jz=-1state.
G: Infinite potential well. The probability for the ground state of 2a-width well going to the ground and first excited state of 2b-width well.
R: Problem of moving a piston between water and ideal gas. (more details omitted)
G: frequency of an oscillator connected to the walls with two springs on both sides.