## Thursday, September 30, 2010

### Judgment Day II

Finally Allahabad HC announced it's verdict one and half hour back bringing a resolution to the 60 year old dispute. The three member bench of HC, comprising justices SU Khan, Sudhir Agarwal and DV Sharma announced the verdict which should keep everyone in this country more or less happy. According to it the disputed site in Ayodhya be divided into three parts: one-third for Hindu Mahasabha, one-third for Sunni Waqf Board and one-third for the Nirmohi Akhara. I was expecting the HC will again ask for out of court settlement, but it's really nice to see the HC coming up with a more realistic verdict. I just wish this is the final verdict on this issue thereby closing this shameful chapter in the History of India forever. I wish every Indian will accept this and come out of the barriers of religion, caste and all to make India a better place to live in.

## Wednesday, September 29, 2010

### A Light Talk on Dark Matter

I gave a semi-popular talk on Dark Matter on Monday afternoon in the department. This talk was organized by Research Scholars Association (RSA), Physics Department and all the research scholars were invited. Although there are more than fifty research scholars in the department, only 15-20 turned up which was however not surprising. There is severe lack of enthusiasm among the people here and some might have been busy with some other important things. Anyway, it was good that not too many people turned up because we could not have the talk in the seminar room (which was booked for a class), but in a small classroom where there were not more than 25 seats. Coming to the main point, the talk I gave was semi popular since people from various working areas were supposed to come and I tried my best to make it as simple as possible. This was my first talk at a popular level and hence was very tough for me. Even after the talk, I was not much satisfied worrying that people might not have got any feeling of such a crucial problem of dark matter in the Universe. My talk went like this: (i) Summary of Standard Cosmology, (ii) Theoretical as well as experimental motivations for Dark Matter, (iii) Role of Dark Matter in the evolution of Large Scale Structure, (iv) Indirect Dark Matter detection experiments and (v) Direct Detection. Most of my slides had diagrams and words only and no equations ;-) Anyway it was a good experience for me to speak at a popular level. I am hopeful of preparing more such talks in future and keep this activity going on.

## Tuesday, September 28, 2010

### Judgment Day

There have been lots of anxieties among the people of India regarding the verdict of Supreme Court in the Babri demolition case. The mosque at Ayodhya was destroyed by Hindu activists two decades back which resulted in communal riots as well as many terrorist attacks by Muslim fundamentalists. This is probably the most difficult case Supreme Court ever had to give judgment to. Initially Allahabad High Court ordered out of court settlement between the two groups Hindu and Muslim but both the groups rejected and appealed in the Supreme court. After lots of drama like shifting the Judgment day and all, finally the court gave Judgment today saying it has rejected the deferment of High Court verdict. I found the verdict very obvious and not surprising at all. In a country like India, where you do not have to make lots of effort to fuel a communal fight among two communities, a verdict on such a sensitive issue in favor of one community would be too much to bring chaos in all parts of the country. Already there is so much trouble, both internal as well as external and specially when the Commonwealth Games is around the corner, nobody would like to take the risk of such a disaster which will indirectly affect the games as well. Although today Supreme court said that on 30th September , Allahabad High Court will give verdict on the case, it looks very trivial. The High Court will definitely stick to its earlier verdict of out of court settlement. I am wondering if a mosque can be built at ground zero in New York, why can't we build something at Ayodhya which will create opportunities for all the communities and not biased towards just one. But it's not as straightforward actually. Even if the court orders to build a University or some trade center may be, it won't surprise me at all if people bring that down also. Indians are yet to come out of rigid religious boundaries. I do not know how to make people realize that there are many important things in this world to which we should pay attention to make world a better place to live in. Text book education seems helpless because you will find millions of Indians who are well-educated (in terms of their degrees) but suffers from religious brain-wash. I think this process will keep going maintaining the tradition of Indian Judiciary system. High Court will always stick to it's verdict, the communities will keep appealing in the Apex court which will again reject it and so on and on....

## Sunday, September 26, 2010

### R-parity revisited!

In Minimal Supersymmetric Standard Model (MSSM), we generally assume the existence of an additional discrete symmetry called R-parity defined as
$R_p = (-1)^{3(B-L)+2s}$
where B, L corresponds to baryon and lepton number respectively whereas s denotes spin. The advantage of this ad-hoc discrete symmetry is that it keeps all the B and L violating interactions away from the superpotential and the lightest super-particle(LSP) becomes stable which can be a good dark matter candidate provided it satisfies other criteria as well. There are some models where this discrete symmetry gets spontaneously broken and we loose some of its benefits. Although the most dangerous B violating terms (leading to proton decay) remain still away, but L violating terms come into the model as a result of spontaneous symmetry breaking. These terms are not very dangerous if parametrically put under control. We can in fact see some signatures of these in ongoing experiments like Tevatron and LHC. But the LSP will no longer be stable in this case and we loose a dark matter candidate. But it is not a very serious problem that gravition (superpartner of graviton) is always there to satisfy the criteria of a good dark matter candidate in any R-parity violating model. Since gravity is very weak, gravitino can have a long life time even if R-parity is broken in the model. In fact such spontaneously broken R-parity models are much better than R-parity conserving MSSM. Initially what I used to assume that R-parity conserving models are good enough to explain the low energy phenomena as well as dark matter. But when I was trying to arrive at non-zero neutrino masses by adding right handed singlet neutrinos, R-parity gets explicitly violated at the superpotential level. Of course if we break R-parity explicitly at the superpotantial level, we can not keep the other B and L violating terms away from the superpotential. The only way to get rid of this problem is to fine tune the B-violating terms to make proton stable enough and keep L-violating terms so as to give rise to neutrino mass. This fine-tuning does not look elegant but we need to do this to explain another hierarchy problem in case of neutrino mass (why it is so small compared to other leptons and quarks). We could have realized spontaneously broken R-parity in MSSM (without right handed singlet neutrinos) by sneutrino (superpartner of left handed neutrino) vev. But that will break lepton number (a global symmetry) spontaneoysly and will give rise to Majoron which will couple to Z-boson and hence ruled out from precision measurement of Z-decay width. Thus R-parity conserving and spontaneous R-parity violating MSSM are not good enough to explain all the low energy phenomena. We need to consider either explicit R-parity violating MSSM (which needs lots of fine tuning in the R-parity breaking sector) or go beyond MSSM by enlarging the Higgs sector or gauge symmetry.

## Saturday, September 25, 2010

### End of a busy week in an awesome way :)

I was pretty busy for last 2-3 weeks. I know the word busy sounds very unusual with me. But this exception happened this time due to accidental presence of my guide in the institute campus for almost one month. Just like accidental presence of some symmetries become useful for us in Physics, so did my guide's presence, in a academic sense of course. I could almost finish editing my draft with him. We sat together 3 times (twice in his home), and edited it. I have to go through it carefully now and mail it to him for his approval so that it can be uploaded in arXiv. Editing the draft was not a very heavy task, but I had to be busy waiting for him in the department the whole day ;) . Out of them some days were successful when I could meet him. Apart from these three days when we edited this draft, there were some other discussion sessions as well where other group members also came to discuss on another problem which we are doing right now on metastable vacua in supersymemtric theories. Anyway after being busy with editing the draft, giving talks, taking part in discussions and of course waiting for guide in the department finally yesterday I said bye to him for next three months ;-) Last night I went for a party thrown by one of my senior in one of the canteens in the campus itself. That canteen has the peculiarity that they arrange such party if informed earlier. They cook the items separately in a much much better way than they serve usually. Yesterday the food was amazing and reminded me of my home food. Another awesome thing was today's football match between the students of our department. After a gap of more than 2 years I played football, that too with bare foot. Although I played for just half an hour, it was really nice. It's difficult to play such a tough game after such a huge gap. Anyway, my busy days are over now, don't have to go to the department for next three months except the day when I have TA duty :)

## Tuesday, September 21, 2010

### What's going on in this country?

I usually try to keep myself indifferent to politics, media and all. But it seems too much now to keep myself so. I do not know if me as well as billion citizens of India are being fooled around by the stupid media here or is it really true that everything is going wrong across the country (except the stock exchange probably). The only good news I see nowadays is that the boom in stock exchange, creating new and new records. But these stock exchange records hardly make any difference to the poor in this country. Although economics is something I hardly understand, but I can definitely say that these so called economic boom is creating an absolutely wrong image of the country in the world as if we are really developing a lot. The poor-rich hierarchy is increasing like anything in this country and only the rich people's growth gets reflected in the sensex mirror. Anyway this is not a new issue in this country, it has been like this always and nobody pays much attention to it unless the sensex crashes. India has been facing so many internal problems recently starting with the Maoists who are as worse as terrorists but somehow our politicians are protecting them saying they are son of this country only. The second turmoil is the Commonwealth Games (CWG). Although it was a matter of proud when India won the bid to host this prestigious event, now I guess most of the citizens feel it to be shame now. Nothing is going well with this event which is scheduled to be started on 3rd October 2010. Looking at the present situation I seriously doubt if it is going to happen at all or not. After missing deadline many times, the whole organizing committee is found to have misused the funds allotted for the event. Not only that, the stadiums they prepared are not up to the mark and yesterday it came in news that the Accommodation at the Games village was too below international standards as complaints came from many foreign delegates. Today a foot bridge collapsed there adding one more feather to the CWG cap. The billions of people in the country have been made laughing stock in the world just because of some corrupted politicians and bureaucrats. While the government might be focusing on this CWG, on the other side Kashmir is boiling like never before. The ongoing protests there have crossed 100 days as well as 100 casualties so far and no agreement, understandings have been reached so far between the government and the separatists there. The hard-line separatists now want Kashmir committees in both India and Pakistan for some reason I do not understand. I seriously doubt whether those separatists want Kashmir to be an Independent country or a province in Pakistan or China may be. This unrest in Kashmir has also brought a serious concern of safety in the country specially in the CWG event in Delhi. I hope everything will remain alright at least till the end of this event.

## Saturday, September 11, 2010

### Competition vs Collaboration

There was a recent discussion in the high energy physics community whether to run Tevatron at Fermi National Accelerator Laboratory, Batavia, Illinois. It is said that many top scientists including Nobel Laurette are suggesting an extension of another three years after the proposed shutdown in 2011. People are saying that Tevatron is not dead yet and it still has a great potential to search the Higgs boson. I agree upto this point. But I found some comments like this also : "Fermilab researchers have a chance to see the Higgs boson first because the more powerful Large Hadron Collider (LHC) at the European particle physics laboratory, CERN, near Geneva, Switzerland, is running years behind schedule and is going to be shut for around 15 months in 2012 for some repair work". I do not understand the meaning of competing with the CERN. After all, LHC is an international collaboration and the US is also contributing to it. Running Tevatron for another three years is a good thing provided it has a potential to discover some new physics beyond the standard model, like it has recently seen some dimuon asymmetry which is 3.2 sigma away from standard model predictions. But the motive to run the Tevatron should not be just to compete with CERN. We should compete with Nature to unfold her secrets, (no matter how hard She tries to hide them) rather than spending billion dollars just to compete amongst ourselves specially during a time when there is a crisis in the global economy. We should also save some money to build the proposed ILC (International Linear Collider) which is supposed to confirm whatever LHC finds :)

### Metastable Vacua!

Yesterday I gave a talk on Supersymmetry(SUSY) breaking in a metastable vacua in the department. It was kind of discussion session which I started by giving a summary on this topic, specially the famous paper hep-th/0602239 (ISS) which has currently 345 citations. Metastable vacua is basically the ground state of a theory which has finite lifetime. Generally we encounter ground state which is perfectly stable and has infinite lifetime. But there are some theories where there can be multiple vacua which corresponds to different ground state energies. Suppose one minimum corresponds to ground state energy e and another corresponds to E. Now the tunneling between these two vacua will be negligible if
$(E-e) \ll 1$
Thus although the vacuum with ground state energy E is not the true vacuum, yet it can be very stable and can have a life time same as the age of the Universe.

In the theories of dynamical SUSY breaking, SUSY is broken at the tree level, and it is restored non-perturbatively at high energy. Thus there are two vacua, one corresponds to the one with SUSY breaking and the other SUSY preserving. Since SUSY preserving vacua has ground state energy zero, this means our Universe (where SUSY is broken) is in a metastable state now. Just imagine what will happen if the Universe suddenly decays to the true vacuum tomorrow ;-). We will meet our superpartner friends then. Anyway the ISS paper which I mentioned above talks about these issues. They start with a SUSY QCD(Quantum Chromodynamics) based on a general gauge group
$SU(N_c)$ with $N_f$ flavors of quarks. This theory is asymptotically free (which means the couplings become strong at low energy and quarks become almost free at high energy) like our usual $SU(3)$ QCD. This theory is strongly coupled at low energy which makes the low energy computations go out of control. But the good thing is that this theory is dual to $SU(N_f-N_c)$ theory with $N^2_f$ singlets and $N_f$ chiral fields which transform as fundamental/anti-fundamental representation under this new gauge group. This is known as Seiberg's electromagnetic duality . The good thing is that for $N_f$ smaller than $3N_c/2$ this theory is IR free which means that it is weakly coupled at low energy and strongly coupled at high energy. Thus we can do all the low energy computations with full control unlike in the $SU(N_c)$ gauge theory. This dual theory is found to break SUSY at tree level and preserve SUSY non-perturbatively after integrating out the massive chiral fields. These two vacua are however widely separated in field space and hence there is no danger of one going into another. The SUSY breaking vacuum is close to the origin whereas the SUSY preserving one is far away in field space. Since the SUSY preserving vacuum has zero vacuum energy, the SUSY breaking vacuum is not the true vacuum since it has non-zero vacuum energy. This means that the SUSY breaking vacuum is a metastable one whose life time can be parametrically made as long as the age of the Universe. This duality works for
$N_c +1 \leq N_f < 3N_c/2$
and it is easy to see that this does not hold in case of minimal supersymmetric standard model (MSSM) for which $N_c = 3, N_f = 6$. But no matter how close this framework is to the reality, it is very impressive from a theorist's point of view and that's the reason I guess why people all over the world is taking this model so seriously. It would be worth studying in fact, how this theoretical framework can be used to arrive at the MSSM with TeV scale SUSY breaking.

## Sunday, September 5, 2010

### কোনে কৈছে মই কবিতা লিখিছো বুলি......

তোমাক হেৰুৱাই মই সুখী বুলি নাভাবিবা
থিক হেৰুওৱা নহয়,
তোমাক মোৰ পৰা আঁতৰাই ৰখা বুলি ক’লে বেছি ভাল শুনি
কিন্তু মই জানো সেইটো বিচাৰিছিলো ?
তুমি তো মোৰ ভাল পোৱাক কেতিয়াও সন্দেহ কৰা নাছিলা
তেন্তে তোমাক এই শাস্তি মই কিয় দিছো ?
এই কথা হয়তো তোমাক মই বুজাব নোৱাৰিম
জীবনত যে সকলো সিদ্ধান্ত নিজে ল’ব নোৱাৰি
সেইয়া বুজাত যেন বহুত পলম কৰি দিলো মই
তুমি মোক ক্ষমা ক’ৰিলেও হয়তো
তোমাৰ ভাল পোৱাই নক’ৰিব
আচলতে ক্ষমাৰ যোগ্যই নহয় মই
তুমি কোৱা তুমিও মোৰ লগত যাত্ৰা কৰিবা
এই নিঃসঙ্গতা নামৰ নাওখনত
হয়তো এয়াই মোৰ শাস্তি
প্ৰতিটো মুহূৰ্ত্তই যেন মোক সোঁৱৰাই থাকিব
মই তোমাৰ প্ৰতি কৰা অন্যায়ৰ কথা
তুমি আগবাঢ়ি যোৱা, মোলৈ বাট নাচাবা
মই কৰা ভুলৰ শাস্তি নিজক নিদিবা
বিচাৰি লোৱা এটি নতুন জীবন, সুখী হোৱা

(Thanks to
for providing an opportunity to type in my mother-tongue Assamese)

## Thursday, September 2, 2010

### The Sun is showing its face after a long time!

After a long time, the sun has shown it's face in Bombay. After the monsoon arrived in June, there was hardly any sunny weather here. It rained a lot this time, highest rainfall in last seven years. Although there are clouds in the sky today, but still the sun is showing up in between. I was never so desperate to see the sun in my life like this time. I always used to love rainy weather as well as winter, may be because when the sun comes up it becomes unbearably hot in most parts of India. But may be this year, the rain was too much for me. Gloomy, cloudy weather for such a long span of time is really depressive as well as unhealthy. I can imagine now why people in Europe and other parts are always so excited about sunny weather. The winter there would even be worse that the monsoon in Bombay I guess specially in northern European nations. I am wondering what would happen to me if I do not see the sun for like six months or so....:-o

## Wednesday, September 1, 2010

### Non-Academic Leave!

I am planning to take Non-Academic Leave for around ten days next month. It has been a long time I have not taken this type of leave ;) Whatever leave I have taken this year are all part of my academic leave which does not have any upper bound. But personal leave can be maximum of thirty days in a year and they are not cumulative :( Thus it is better if I make maximum use of it every year. I am planning to go home next month during the Durga Puja vacation. I was not planning this although. I wanted to go home in December, but that has become unlikely since I might have to go to Jaipur for DAE Symposium (http://heps.lnmiit.ac.in/). So better I should go next month itself to get the Durga Puja festival as a bonus. I do not have much work load also except the two papers which I am trying to finish. The only thing I am worrying is the TA duty in that week. I need to find some guy who can take the responsibility of that for the particular week. I do not know exactly what will happen if I do not find a substitute to do the TA duty for that week and go home. May be the department will cut my stripends, which I won't mind much anyway :)

### It Feels Good!

After more than one year gap, I finally met my supervisor :-) It feels great indeed, and he could recognize me as well ;) Actually this meeting was supposed to happen couple of months later, but he had to come to the institute for some emergency reasons and we end up meeting unexpectedly. For the last one year we are working on a problem, written 2-3 versions of a manuscript but still have not been able to finalize it. It's really difficult (at least for a beginner like me) to do work by just communicating through email. Let's see if something can be done in this direction during his one month stay here although I am not much hopeful about it. In the meantime I am trying to finish some of my own work which might lead to a publication if the results are correct which I have to re-check :)