String Theory Video Lecture Part 4

Yesterday we had the 4th weekly session of watching the string theory video lecture by Prof Shiraz Minwalla. Unfortunately the seminar room was occupied by some people and we had to move to an another room where I could not not configure my laptop with the projector and after trying for more than half an hour we decided to watch the video in the laptop only. In this part of his lecture he talked about tachyonic states in bosonic string theory and showed how 26 space-time dimensions appear naturally for the consistency of the theory. But the ground state of the theory still remains tachyonic. The first excited becomes massless for D=26. Since the 1st excited state behaves like a vector which has D-2 components and hence transform under SO(D-2) it can not be massive which transform under SO(D-1). I was wondering if we fix N=1 (1st excited state) in the the relation $$ m^2 = \frac{2}{\alpha}[ 2N-(D-2)/12] $$ and requiring this state to be massless, arrive at D=26 how would the same value of D would make the second excited state massless. Then Prof Ramadevi cleared my doubt saying that the higher excited states are Higher dimensional representation of SO(D-2) and hence need not be massless. Then he talked about $$ N= \tilde{N} = 1 $$ where the tilde means the right moving ( in case of closed string we have both left and right moving fourier modes). This corresponds to $ 24 \times 24 $ representation of SO(24) which will give rise to a massless symmetric tensor field $G_{\mu \nu}$, a massless antisymmetric tensor field $B_{\mu \nu}$ and a scalar field $ \Phi$ called the dilaton. Thus gravity comes out automatically in closed string theory. After that he gave a brief introduction to path integrals which he will probably use in his next lecture.


Its surprising to see more voter turnout in Arunachal than Maharashtra..:)

What a surprise! Almost 72% voter turnout was recorded in Arunachal Pradesh whereas only 60% in Maharashtra during today's Assembly elections. In a state like Arunachal Pradesh where there is hardly any kind of development, or which hardly get any kind of central government attention, people seem to have more faith in the political system than a state like Maharashtra, the capital of which is also the financial capital of the whole country. As a resident of the neighbouring state Assam, I always feel that North-Eastern states like Arunachal Pradesh are completely neglected by the Central Government in terms of infrastructure,transport, education, Industry and many others. It is needless to say that Arunachal has much better potential in terms of natural resources and tourism compared to most of the states in India. People become serious about Arunachal only when China says something related to Arunachal. It is quite well known that China claims several thousand square kilometers in Arunachal to be a part of its own territory which India always keeps denying. But instead of this cold war with China over Arunachal, I believe the Government should work more for the development of this state. Specially looking at such an impressive voter turnout which reflects the fact that people have faith in the great Indian Democracy there is absolutely no reason not to work for a better Arunachal.

Dark Matter and Black Hole!!

A few days back, I was having an interesting discussion with one of my friend in a public forum known as Actaphysica http://www.actaphysica.com/ . He seemed to be an expert in Black Hole physics who opened various threads related to some interesting aspects related to black holes, hawking radiation(HR) as well as dark matter. He talked about the possibility of a black hole formed out of two unstable micro black holes. As we know the black body temperature associated with a black hole in inversely proportional to the mass squared. Thus smaller the mass is , higher is the temperature and sooner the black hole will evaporate. I had a doubt while discussing the possibility of an atom formed out of a black hole with charge -1 and mass $m_e$ which we call and eBH (electron black hole) and another with charge +1 and mass $m_p$ which we call a pBH (proton black hole). I raised the doubt saying that eBH being tiny will evaporate soon by emitting HR and hence there won't be any bound state forming between eBH and pBH. But my friend pointed out that only isolated black holes can radiate HR and finally evaporate. Thus within a bound state eBH and pBH won't be emitting HR. However if the radius of their bound state is smaller than the corresponding Schwarzchild Radius then the bound state itself can behave like a black hole and hence emit HR since the bound state is an isolated state by itself. This would be , according to him, a ground breaking result since so far people have no idea about internal substructure of black holes. One more interesting aspect of such bound state could be the relation with dark matter. If the bound state does not become a black hole then it would be a stable entity and hence can be studied from dark matter point of view. I do not know how much work is done in this direction but it seems like an interesting field to explore.

A purely supersymmetric origin of neutrino mass

Yesterday I came to know about a completely supersymmetric(SUSY) origin of tiny neutrino mass, that is, in the non-SUSY version of the model neutrino mass remains either zero or comparable to lepton/quark masses. This comes when neutrino mixes with the neutralinos in the Supersymmetric model. The neutralinos are the mass eigenstates of neutral gauginos as well as Higgsinos. Neutrinos can mix with the neutralinos only if the sneutrino field get a vacuum expectation value (vev). Diagonalizing the mixing mass matrix will give rise to a small neutrino mass by sutable adjustment of different scales. However since neutrino/sneutrino carry a lepton number whereas neutralinos do not, such mixing violate R-parity. This R-parity violation however should not lead to dangerous proton decay, but it will make the standard neutralinos decay into neutrinos. If neutralino is to be a dark matter candidate, the relic abundance will put a constraint on the R-parity violation. Thus this scenario will be tightly constrained by smallness of neutrino mass as well as dark matter relic abundance. I am trying to see if there is any other advantage of this approach, say from the point of view of recent positron excess measured by various dark matter indirect detection probes.

Quantum Foundation Lecture 3 cancelled without any email notifications...

It was really embarrassing yesterday when I was sitting in the P C Saxena Auditorium for almost 20 minutes along with 6-7 other students hoping that sooner or later the lecture will happen. But I finally gave up and went to the physics department which is ten minutes walk from the auditorium. There I saw a small notice saying that the lecture has been canceled due to health problem of Prof Roy. But there could have been a better way to communicate the message. In fact, the people who used to make the video recording of the lectures also came to the auditorium and preparing for the recording when I left the place. I have no idea how long they as well as the other 6-7 students were waiting there. At least the message could have been put in the auditorium notice board. I don't think I will be enthusiastic enough to attend the remaining lectures. May be it is better to look at the lecture slides which will be put in the department website after the lecture ends.

Quantum Foundation Lecture part 2

Today's lecture was more like a question answer session. It was natural that students will come up with many doubts after yesterday's overdose..:P. Most of the time Prof Roy had to answer very basic doubts raised by the students. He started with two comments regarding yesterday's class: Bell's inequality is fully relativistic and violation of local reality by Quantum Mechanics does not mean that information can carried from one place to another with speed more than the speed of light in vacuum. Then he gave an introduction to density matrix for pure and mixed states. Then he talked about separable pure states. These states are basically non-entangled and obeys local reality, Bell's inequality. He then talked about N-particle correlation function and how difficult it is to find out whether the N particle states are entangled or not. Since violation of local reality grows exponentially with number of particles and so does entanglement, hence it can speed-up quantum computation very efficiently. He skipped the latter half of the lecture since he ran out of time answering the doubts of the students and will probably talk about that in the next lecture which is on 12th October.

Wake Up Sid

Yesterday I watched the movie called "Wake Up Sid" released recently starring Ranbeer Kapoor and Konkona Sen Sharma. Well, I won't say it is a good movie, but an average one. The story was all about Sid, son of a famous industrialist in Bombay and Ayesha, a struggling, hard-working young lady who has come from Calcutta to Bombay in search of work. When they first met, they were just on two opposite poles. Sid was very childish, immatured whereas Ayesha was well focused on her dream of getting established in Bombay. The story basically shows the transition of Sid from a stupid boy into a self-established hard working man. It has a happy ending where Sid becomes quite matured, hard-working and independent young man to make himself upto Ayesha's mark and live together. As it is obvious by now, the story has not much depth as we expect in a movie starring Konkona. I have no idea if I would have even bothered to write about the movie if Konkona were not there...:P. But I would obviously rate this movie thousand times better than movies like KANK, another Karan Johar film. The movie reminded me of a news which I saw in Times of India few days back which said Karan Johar had to apologise for using the word "Bombay" instead of "Mumbai" in this movie. I don't see what is wrong in it, after all so many people are still used to Bombay instead of Mumbai, Victoria Terminus instead of Chattrapati Shivaji Terminus etc and Karan might have just picked up two such real persons in his movie.