b***y
发帖数: 14281 | 1 不是massless electron。是说因为其费米面呈现锥形，类似Minkovski space
里的light cone，所以这个系统里的fermionic excitation appears like a
single massless Dirac fermion. But, No. 1, it's not really "massless"
because the so called "mass" here is an analogous concept since
the fermi surface is of course not the real light cone and its slope
is not the real speed of light, and No. 2 it's an approximation. Of
course no exact conic fermi surface is possible in a real physical
system. It always gets smoothed out at the tips.
.. |
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h*****9
发帖数: 6643 | 2 没听说过是你自己无知。这只能说明你是个很容易被骗的无知之徒， 你又要凭你自己的无知骂人，你又无耻了。
揭露 BIG-BANG 是披着科学外衣的宗教，这在10年前就有很多文章了。
THE "BIG BANG" IS JUST RELIGION DISGUISED AS SCIENCE
by Michael Rivero
Once upon a time, a long time ago, there was this guy named Aristotle.
Pretty sharp fellow; he thought up a lot of good things. But, occasionally
he made a mistake.
One mistake he made was to toss an orange up in the air and watch it come
straight back down to his hand. Aristotle reasoned that if he was moving,
the orange would have flown... 阅读全帖 |
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R**********n
发帖数: 523 | 3 为什么这篇文章说是普林和MIT的人发现的？
Two separate teams of researchers have found evidence for a theorized type
of massless particle known as a “Weyl fermion.” The discovery was made by
scientists at Princeton University in New Jersey and the Massachusetts
Institute of Technology, and could herald a whole new age of better
electronics.
http://www.iflscience.com/physics/discovery-massless-weyl-fermi |
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R*k
发帖数: 264 | 4 我也不懂， 不过从wiki的介绍来看还真是突破性的。
http://zh.wikipedia.org/zh/%E7%9F%B3%E5%A2%A8%E7%83%AF
但是这段看不明白：
“Graphene还表现出了异常的整数量子霍尔效应。其霍尔电导=2e2/h,6e2/h,10e2/h...
. 为量子电导的奇数倍，且可以在室温下观测到。这个行为已被科学家解释为“电子在
graphene里遵守相对论量子力学，没有静质量(massless electron)”。”
怎么可能有massless electron？还是只是一个近似？ |
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b***y
发帖数: 14281 | 5 OK, perhaps, it is still justified to say it's really "massless" since
while the speed of light is not the real speed of light, it's still
described by a massless Dirac equation. |
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w**o
发帖数: 39 | 6 吕宏现在还在中央财经大学邹恒甫那个研究院
见北师大物理系的通知
学术交流
Critical Gravity in Four and Higher Dimensions
演讲人单位： 中央财经大学
演 讲 人： 吕宏 教授
主持人单位： 北师大物理系
主 持 人： 马永革 教授
开 始 时 间： 2011年03月31日 15:30
结 束 时 间 2011年03月31日 17:00
举 办 地 点 物理楼106
演 讲 说 明 In this talk, we shall examine four-dimensional gravity with
a cosmological constant and curvure squared terms. The theory was known to
be renormalizable, but it suffers from having the ghost-like massive spin-2
graviton. We demonstrate that there exists a cri... 阅读全帖 |
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p**n
发帖数: 10 | 7 The massless QCD has the global symmetry described by the group
SU(NF)L*SU(NF)R
The Lagrangian is chirally symmetric. The symmetry is spontaneously broken
down when we get into one of the vacuum state. The result of which gives
massless Goldstone bosons. For your 2nd point I do not quite get it. Now we
are in the color space...
BTW, do you think Chiral Purterbation theory is reasonable? Receently it is
found that when we go to the higher terms, the series do not converge. One of
my classmate was |
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发帖数: 1 | 8 我操！老子再说一遍，你那个公式不对，不管你用不用natural units简化。而且，你
给出的网已经清楚地说明，“If the body is a massless particle (m0 = 0), then
(1) reduces to E = pc. For photons, this is the relation, discovered in...",
此句已经清楚地告诉你此公式如果用于光子应该是什么情况，可你还在拿适用于非光
子的情况扯测光子。如果是光子，色散公式变成e=pc或是e=p，这也正是我在前面贴子
已经告诉你的。本贴讨论的主题是光子质量是不是零，你拿着带m项的色散公式测质量
，则那个质量必须是静质量，并且必须不为0, 算了，老子懒得说了，看我回大傻逼的贴
子吧，如果你看不懂，那我跟你也没什么好谈的了。这里的逻辑就象你们搞物理的，连
暗物质到底存在不存在都特么没结论的情况下，你们就能写出很牛逼的公式并精确算出
暗物质的质量和膨胀系数，真尼玛搞笑。 |
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a****p
发帖数: 6155 | 9 难道你们研究怎么用高压把金刚石变成石墨，然后从石墨剥出graphene,再研究一下
Massless Dirac fermions? |
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b*****d
发帖数: 7166 | 10 人类的灵魂是大约2克左右电磁波?? don't you know 电磁波 is massless? |
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S*****T
发帖数: 400 | 11 偶来讲讲关于extra dimension的一点东西吧
先讲讲相对论的时空观
大家可能都听说过那个Minkowski的4位时空理论
（也就是3维的空间和一维时间，空间和时间是等价的）
狭义相对论在那个时空里可以被写成很漂亮的形式
按照P.KLEIN的1872年的Enlargan progam对几何的分类
定义不变量，然后根据变换群对其分类
狭义相对论其实就是minkowski空间的lorentz几何（也可以说是poncare
就是lorentz加上平移）
广义相对论讲的是另外一回事，其变换群是gl(4),空间也不同
minkowski时空的lorentz几何不变量就是minkowski空间的那个距离（我们叫
间隔），定义距离的东西叫度规metric,其实也就定义了什么是这个空间最短的东西，
可以叫测地线geodesic，而这个东西和空间的拓扑结构很有关，（据个例子
一个球面上两点最短距离和一张纸就绝对不同，不过你把纸卷成圆锥，
那条最短的距离还是原来的。广义相对论中的光的运动方程就是沿着这个走。
因为光是massless的。
大家有点概念了，偶就来说说extra dim
这个extra |
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d****z
发帖数: 9 | 12 用量化方法算石墨烯总能会告诉你 "there are two-dimensional gas of massless
Dirac fermions in graphene"?
"用量子计算机计算总能，算得更准更大"绝不是一个聪明人该干的事。
其实前面的什么“Ｎ－representable"的问题是另一类聪明人不该干的，没有一个伟大
的数学家或应数学家觉得这是一个有趣的问题，只有一个加拿大的三流数学家在攻这个
问题，可笑的是他还曾经想让费曼对这个问题感兴趣。
容原理 |
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F****I
发帖数: 270 | 13
>: 用量化方法算石墨烯总能会告诉你 "there are two-dimensional gas of
massless
so what?
你说“你觉得还会有人拿它来进行现在愚蠢的量化热化学计算码”
又没说这个人聪明不聪明
so what? |
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d****z
发帖数: 9 | 14 我觉得“不少搞化学的人认为石墨烯没意思”就是把石墨烯当成另一个碳六十，
而根本不了解“there are two-dimensional gas of massless Dirac fermions in
graphene and so on .....". |
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t**********m
发帖数: 205 | 15 来自主题: Mathematics版 - 伟哥之乐 The joy of viXra
https://telescoper.wordpress.com/2011/05/19/
Posted in The Universe and Stuff with tags arXiv, astronomy, Cosmology,
Physics, scientific publishing, viXra on May 19, 2011 by telescoper
From time to time on this blog I post rants about the state of scientific
publishing, open access, the importance of the arXiv for astronomy and
cosmology, and so on.
This morning, however, I discovered an “alternative” side to the whole
business of online science, a site by the name of viXra. Mos... 阅读全帖 |
|
s******x
发帖数: 15232 | 16 graphite is cheap; graphene is EXTREMELY expensive, if you buy it from the
company(s). the annual revenue of USA can buy 1.5cm^2 of graphene, if I
remember correctly.
grephene's mobility is NOT high. it is orders of magnitude lower than
typical 2DEG. The reason it is still interesting to basic research is:
1. massless dispersion relationship
2. unlike 2DEG, it is on the surface, susceptable to many modifications.
as for application (to use as transistor), one indeed need double layer
graphene, |
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s******x
发帖数: 15232 | 17 CARRIERS HAVE MASSLESS DISPERSION RELATIONSHIP
SO THEY ARE RELATIVISTIC PARTICLES OBEYING DIRAC EQUATION， WITH EFFECTIVE C
~ C/100
可以做许多奇怪的实验，比如KLEIN PARADOX之类 |
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T*********r
发帖数: 11175 | 18 u，d几乎是massless，所以叫unflavor
下一个重的s都上百个mev
到了b都4gev了
因为qcd的coupling在这些scale差的很大
所以pion的hadronization和B_s这样的还是不同的
J,B_s之类应该是可以按照pertubative qcd算 |
|
C***H
发帖数: 508 | 19 也说不上功利化，主要的point还是实现了massless electron，于是可以实验验证多年
没法做的很多理论预言。应用上的potential只是一个方面而已，看不出来是发奖的重
点。 |
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s**********n
发帖数: 868 | 20 呵呵，有喊joke的，有喊悲哀的，喊以前最起码把Nobel官方的scientific background
看一遍吧。
突然觉得，物理学的悲哀不在于诺奖没有颁给最first principle的研究，而在于很多
做物理的人，在这个本来就已经比较小的领域里（相对生化医学工程而言），对同行却
如此狭隘和排斥。
我不是做graphene的，属于半懂不懂的那一类，不过周围有人预测到了这个奖。
我的感觉上是发得稍微早了点，等应用前景进一步明朗可以更convincing一点，甚至可
以考虑和Topological insulator一起发。但仔细想来，graphene即使在现在还是可以
make a strong case的。从fundamental的角度来讲，
1）人类历史上第一次发现真正严格意义上的稳定的two-dimensional material；
2）Graphene独特的电子性质提供了一个massless fermion system及其引起的各种新现
象（如unusual quantum hall effect和Klein tunneling），而且这是一个奇异的在凝
聚态材料可以... 阅读全帖 |
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b******r
发帖数: 45 | 21 In QED, I can simply demand that the theory describes a massless spin-1 part
icle and deduce the U(1) gauge symmetry from it. The same logical route exis
ts for QCD, but it's mathematically too complicated so that people adopt the
reverse route: to impose the SU(3) gauge symmetry in the Lagrangian. In sho
rt, gauge symmetries are a mathematical convenience that is so convenient th
at people just build theories on it.
The term "broken gauge symmetry" appears in many places, but it's a bad and
mis... 阅读全帖 |
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t**********m
发帖数: 205 | 22 The joy of viXra
https://telescoper.wordpress.com/2011/05/19/
Posted in The Universe and Stuff with tags arXiv, astronomy, Cosmology,
Physics, scientific publishing, viXra on May 19, 2011 by telescoper
From time to time on this blog I post rants about the state of scientific
publishing, open access, the importance of the arXiv for astronomy and
cosmology, and so on.
This morning, however, I discovered an “alternative” side to the whole
business of online science, a site by the name of viXra. Mos... 阅读全帖 |
|
a****a
发帖数: 5763 | 23 phonon 难道不是massless的？
还是有什么物理过程让phonon有质量了?
不能用光的速度吧？只知道波长，不知道频率，不是还是算不出来能量么
知道有效质量。这个phonon的质量一般怎么取呢？ |
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j**p
发帖数: 53 | 24 In principle, nobody says graviton should be massless (just like photon) and
travel at the speed of light. It just happens to be so -- at least all
experiments so far haven't shown otherwise.
It would be interesting, if, similar to weak interaction, graviton has mass,
rendering gravitation short-range. Our whole world would be very different.
But maybe life wouldn't exist in such a world and we wouldn't be here
talking about this. |
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L*m
发帖数: 235 | 25 2015诺贝尔物理奖
获奖人：Arthur B McDonald、Takaaki Kajita
获奖领域：实验高能物理
获奖原因：发现了中微子震荡，并因此证明了中微子具有质量
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|
s**e
发帖数: 103 | 26
now there is speculation about the correspondance between the charged
blackhole and the tower of massive Kaluza -Klein states. But it's certainly
not the electron which should be massless at that scale. And it's only a
conjecture. |
|
y***u
发帖数: 25 | 27 kaka, my question was: if as u said:
"One fundamental
then, in SUSY, how to explain? If I remember correctly, gauginos can also be
the media of interractions in SUSY. Also, in scalar gauge theory, I can not
see how your explaination works, since we got no fermion there.
Actually, I do not know how to answer this question either:), maybe
microsystem can give us a standard answer? :)
Just for fun, the second question comes:
In massless QCD, flavor U(3)L*U(3)R is spontanousely broken to U(3), then |
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