A Quantum Diaries Survivor

Jeff pointed out to me today the remarkable world wide telescope, a site where you can download a software created by Microsoft to browse the heavens as if you were commanding a powerful telescope. The constellations are not maps, but actual pictures, into which you can zoom as much as the images of the digital sky surveys (SDSS and others) allow.

My jaw dropped as I started using the software, which you can download and install on your computer, and which works pretty much like google Earth - downloading the region you are visualizing from the internet. A nice feature is the appearance of a frame of thumbnail pictures around the zoomed area, highlighting the most interesting celestial objects present there. If you click once on each pic the relevant object is highlighted on the map; clicking twice will allow you to download full-resolution image of the object directly from the online databases, including Hubble images.

What I find amazing, however, is the fact that browsing the night sky becomes a thrilling experience at your fingertips in front of the computer. The realism is perfect - these are pictures, in pure google earth style. However, while we never have the need to find a feature on the Earth surface by hovering over it in our real life, that is exactly what we do when we observe the night sky: so the learning experience provided by the program for a user who wants to get better at locating celestial objects is invaluable.

Above you can see a screenshot of part of the WWT window, which I centered on the Deer Lick group of galaxies - NGC7331, a milky way-like galaxy which is the largest member of the group, is on top. Below you can see Stephan’s quintet - a group of five small galaxies of 13th-14th magnitude which is among my favorite targets in deep-sky observing sessions. By zooming in (below), you get to see stars fainter than 18th magnitude, at a resolution comparable to that of  a meter-class instrument. Amazing!

I highly recommend downloading the software. Learning to locate objects will become a wonderful pastime!

I listened carefully to Antonio’s talk this morning at the final session of the 2008 conference “Neutrino Oscillations in Venice”, for two reasons. One is that the director of INFN-Padova is well-known for giving exceptionally clear and insightful talks, and the other is that he will speak of the theoretical side of dark matter searches at the LHC just before I deal with experimental details of the same topic, next week in Padova. So I am able to offer you a rather detailed report of his speech, with the note that I am solely responsible for omissions and mistakes. Another caveat is that these notes are not for outsiders: sorry, but making the text below understandable for non-physicists is just above my possibilities. I will expiate soon with a more accessible discussion of the same topics.

The purpose of Antonio’s talk was to discuss what we mean by complementarity of LHC with the effort going on in astroparticle physics to look for new physics at the electroweak scale.

We can foresee two different scenarios. In the first one, LHC is turned on and very soon discovers new physics: this is what most of us (not me) believe and all of us (including me) hope. In this case, it could be difficult, if not impossible, to reconstruct the fundamental theory lying behind those signals of new physics: that is, even if signals were evident, it would be hard to trace back to which kind of SUSY theory gives rise to these particles. All these questions will be very difficult to address in a hadronic machine. We thus need additional, independent information.

The second scenario occurs if LHC has difficulty finding new particles apart from the Higgs boson.
Indeed, we insist on the presence of new physics at the electroweak scale for the sake of stabilizing the Higgs potential. Such a stabilization could however jolly well imply the presence of new particles at the TeV scale but not below. In this case LHC could have trouble finding new physics. Having a complementary tool to address these signatures of “low-energy, but above the TeV scale” new physics becomes important.

Thus, very important besides LHC are the complementary roads, one linked to Astroparticle Physics, in particular the issue of dark matter and the issue of baryogenesis, which are keys for this complementarity to LHC; the second is the high-intensity road, in particular the study of flavor-changing neutral current phenomena and CP violating phenomena and their relation to lepton flavor violation in neutrino physics.

Today, what are the observational reasons pushing us beyond the SM ? The traditional road of high energy physics as much as that of flavor physics did not lead to any conclusive evidence for physics beyond the standard model. We have some possible hints, such as the 3.something discrepancy from theoretical estimates in the gyromagnetic factor of the muon, and some three-sigma discrepancies in transitions. Concerning the latter, a month ago there was a study showing some discrepancy from SM for the phase in mixing. We have some possible indications, but however how much we can like this approach, we have to admit that after thirty years or so of searches for discrepancies we did not get any firm evidence for deviations from SM yet.

To go beyond the SM the observational evidence may come from astroparticle neutrino physics and cosmoparticle physics. It can be interesting to put one close to the other: the standard models we have for particle physics and cosmology. If we put the two models together, their marriage is a quite happy one, with incredibly successful fruits, such as the clear picture of the big bang we have with studies of nucleosynthesis. However, fortunately enough, there are some points of friction: some pepper in the marriage. This points of friction are a clue for us that there is new physics either beyond the standard model in particle physics, or in cosmology. We should keeop in mind that both the options are present together.

Besides the issue of neutrino mass, the three main points of friction are dark matter, matter-antimatter asymmetry, and inflation. This kind of Michelin rating in stars (dark matter gest three stars, matter asymmetry gets two, and inflation gets one) for these three topics reflect Masiero’s point of view about their relevance to individuating new physics. Dark matter is the major issue in this context.

Before going to dark matter, Masiero discusses the matter-antimatter asymmetry in the universe. If you want a dynamical mechanism to produce the asymmetry starting from a symmetric early universe, you need some new physics (NP) beyond the particle physics SM. Indeed, after many years of a lot of work trying to produce baryons, we concluded that we need new physics. Which kind of new physics can produce the matter-antimatter asymmetry ? It is very tempting to adopt the view of it coming from lepton-antilepton asymmetry through the decay of right-handed massive neutrinos. It is appealing trying to build up upon the existing models created for other purposes: this is the case for heavy right-handed neutrinos, which were introduced from neutrino mixing observations. Introducing a new source of CP violation in the leptonic sector may have important links with CP violation in neutrino mixing.

The seesaw mechanism brings in a new element: if you insist on right-handed neutrinos and if you like to have Supersymmetry (SUSY) at least at the large scale, then you are led to a SUSY seesaw mechanism. In that case, it is given as a bonus because of the running from the large scale that you generate large lepton flavor violation in the scalar sector of the leptons. The important message here is that if you consider lepton flavor violation, you can probe this region of parameter space of SUSY seesaw models. The muon decay experiment looking for the reaction , MEG, can give bounds on the mu-egamma branching ratio at or about . These foreseen further two orders of magnitude of improvement in the branching ratio for MEG are not just important for making it to the PDG booklet, but also because it enters the heart of the region for SUSY seesaw models for lepton flavor violation (LFV). Something similar exists for the decay, which will reach a bound in branching ratio. We have to keep an eye to these LFV phenomena because they might give very important surprises even before LHC starts being operative.

Concerning inflation, again the main message to bring here is that if one wants to have an inflationary epoch in the early universe it is not possible to use a simple scalar potential of the standard model. One needs to do some heavy gymnastics to produce inflation. It means that if one wants an inflationary epoch in the Universe evolution, one needs an extension of the SM in the scalar sector, and the polarization of cosmic microwave radiation can evidence the new scale in inflationary physics, likely to be much larger than the mass of W or Z bosons.

No matter how important these four roads are, neutrino masses plus the other three just mentioned, they do not indicate which new scale could be present to produce new physics necessary to give neutrino mass, dark matter, baryogenesis and an inflationary epoch. There is no indication of where this scale could be. The only indication we have that the first NP is accessible through LHC comes from theoretical arguments: we need this stabilization of the electroweak scale, and it is thus better -more comfortable- to have the NP at the same scale. This is the major argument we have. There is a second point: the strong indication that we have from SM that there is some kind of unification of the fundamental coupling constant may point in the direction that the SM meets some kind of low energy completion in order to achieve the correct unification of these couplings. Either the SM tells that the three couplings show some trend to acquire a common value at a high scale, some new physics could be introduced to achieve a good unification at a larger scale. This is a 1-star support, because there is a lot of theoretical prejudice which enters this kind of argument, but it is still appealing.

What is important from a pheonomenological point of view, is that we have in our hands a powerful tool to assess this high energy scale, one handle to access this scale is related to proton decay. This is important thinking in a talk about astroparticle physics: proton decay must remain a complementary access to this high scale in addition to baryogenesis and dark matter tools.

Masiero focused on two numbers, enormously important for us: , the baryon number density, and . Their clash is very significant indication that we have NP beyond the SM; the non-baryonic dark matter is the most striking evidence we have of NP. Neutrino mass is just an addition to the SM, but in the case of dark matter it is even qualitatively new physics. You really need something new to account for this result. Alternatives related to deviations from standard gravitation, like MOND, have failed when studies of the bullet cluster were produced last year. In fact, we can use this cosomological argument to have in sight the neutrino masses. Instead of using neutrinos, we can use the cosmological argument to infer information about neutrino masses and properties.

Concerning dark matter, the strongest candidate is a particle in the tens of GeV range, which interacts weakly. Saying this does not mean that it is really the only candidate or in any case the most favorite one. It is the strongest because as it was pointed out, there is this amazing coincidence that putting together parameters that do not know each other, you end up with a density of WIMPS (weak interacting massive particles) which ends up in the ballpark to account for dark matter. The argument is that the density of WIMP particles which could be interesting to explain dark matter is of the order of , which is exactly what one finds if one hypothesizes GeV or so.

Of course in the history of physics we had other instances of remarkable coincidences that did not lead to the discovery of something new about Nature. Nature could be more original and creative than we are, so one should not emphasize too much this result, but this coincidence deserves further study. There is a convergence of two independent sectors, particle physics and cosmology conspire to give this kind of number.

Interestingly, if you ask about candidates for WIMPS, all the examples of new physics at the electroweak scale produced in recent years provide candidates: stable particles which have some kind of weak interaction in the range of 100 GeV. They can be bosons, scalars, etc. The message is important: a WIMP candidate could at the same time account, enter in a extension of the SM to provide a stabilization of the electroweak scale, and at the same time provide a candidate to solve our problem with the accounting of matter in the universe.

If you want to stick to the SUSY possibility of this WIMP, Masiero feels the need to insist on a point that sometimes people forget, which is that SUSY in itself does not predict a neutralino! If you write a SUSY lagrangian, in general you do not find a stable scalar. Since you want to eliminate terms that are dangerous for the violation of baryon and lepton number, so because of the proton decay problem, we add to the SUSY theory a new symmetry, this famous R-parity, and this makes the theory predicting a stable particle. So this connection between baryon violation and predicting a new stable particle is to be taken with care.

The lagrangian of any SUSY contains more than a hundred parameters. So when one talks about a “minimal” SUSY model, one has to buy at least 124 parameters. One then gets “reasonable” by having five independent parameters, which one can do by making reasonable assumptions. These are , , , , . Then, when you say “this is the prediction of SUSY” you give the impression that you give a prediction in a model. But SUSY is not a model but a framework. You can find very different kinds of light supersymmetrical particles. Gravitinos, for instance, could just as well be the light particle. You could make a gravitino with 1 keV or 10 keV which could play the role of the light particle.

The SUSY parameter space of this so-called “constrained minimal supersymmetric extension of the standard model”, CMSSM, is 5-dimensional, and there is a small region where you have
suitable production of dark matter. There are narrow bands in the SUSY parameter space in the plane when you consider the CMSSM. These results rely on a belief that so far has not any strong scientific support, that is that we know how things went in the early universe before nucleosyhnthesis. We are making an extrapolation of standard cosmology before nucleosynthesis. Nucleosynthesis is the first moment from where we have testability of the evolution of the Universe. We cannot observe the Universe before then.

This brings to the important issue of dark matter and radiation. We have become accustomed to sweep under the rug the problem of dark energy (DE). There could be a relation between the problem of DM and DE. For instance, if you decide to make some modification of gravity to account for DE, this can completely spoil the picture of your cosmology before big-bang nucleosynthesis took place. This creates a major departure from standard cosmology.

The presence of a WIMP today as the DM candidate implies some constraints on its annihilation cross-section: it exists, so it is rather stable. You can correlate annihilation to production, and create a link with how many of these particles can be produced at a collider. One would like to find this DM directly. One of the highlights of this meeting was the result of DAMA-LIBRA. A consistent result for 11 years, plus the statistical relevance we have at the moment for the modulation effect.This badly calls from our community to have some independent confirmation. This result is so important that it is mandatory that we make a major effort to confirm it independently.

How far are we in DM searches from some possible threshold to find this WIMP particle directly? This

brings to some evaluation of the cross sections in SUSY . We are three orders of magnitude away to probe multi-TEV SUSY, which could be difficult to access with LHC. The testable region by LHC is smaller than that accessible by dark matter searches. It must be mentioned in this respet that we are thus at an important stage now. In a month we have the launch of GLAST, which is very relevant to cover the region below 100 GeV. It could detect gamma rays from the annihilation of dark matter candidates, and it will extend our sensitivity in a range not well covered so far. In general, LHC searches for dark matter, and those that may follow at ILC, are complementary to the other searches because they cover different parts of the parameter space.

A recent roadmap of APPEC (the Astroparticle coordination in Europe) shows seven different experiments that may play a key role in giving us complementary information about dark matter. Funding of these experiments is off by a factor of two, but we can try to push all of them. We must thus make an effort from the scientific point of view to insist on the validity of this astroparticle tool to have this access to new physics at the electroweak scale. Together with them, the effort on flavor physics (a super B machine could be relevant to explore the 1% REGION of the flavor parameter space, to find a discrepancy with SM) and the LHC are crucial. All this together should make us able in the next decade to finally clear
up what is the center of this new physics at the electroweak scale.

The slides of Antonio’s talk can be found here.

The new result of the DAMA-LIBRA collaboration, which finds a yearly-modulated signal of interactions in their NaI crystals which is compatible with dark matter in our galactic halo, has caused some ripples in the web. I was surprised to find that a comment I had posted yesterday on the matter was linked by Symmetry magazine as well as by Peter Woit (who was however the true originator of my remark).

I must say I do not particularly enjoy to always sound skeptical. A scientist should keep an open mind, and if the DAMA-LIBRA signal has a cross-section which is apparently already excluded by the CDMS result, as well as orders of magnitude above the estimates for mainstream dark matter candidate models, one should wait before taking a step back, and rather consider questioning the exclusions rather than the signal. Indeed, establishing a signal comes before challenging it with specific models, and the comparison of DAMA’s result with CDMS exclusion contours belongs firmly to the second category. CDMS excludes specific models, while DAMA establishes a yearly frequency in its signal yield which could be due to particles we have still not even conceived.

So, why not focusing on the establishment of the signal ? I tried to build an opinion on the solidity of the DAMA result this morning by talking to a few people who attend the conference, and in particular with a young researcher who now works for CUORE and has been in the DAMA collaboration in the past. She in fact worked at the analysis of data, trying to interpret the modulation in photomultiplier counts with different density models of dark matter in the milky way halo as well as components from our close satellites, the magellanic clouds.

It looks like the phase of the cosine oscillation in signal yield, which is something I had doubts about, is indeed compatible with being zero for a time of the year compatible with June 2nd, which is the date when the Earth travels in the direction of the Sun’s motion in the galaxy (if one forgets about the inclination of the Earth orbit with respect to the Sun’s line of motion). Not perfectly matching June 2nd, but compatible with it.

Another issue is of course the one which was raised at yesterday’s talk: signal efficiency is steeply rising in the region between 2 and 6 keV where the modulated signal is observed. It turns out that the efficiency is not full but it is quite stable - stability is checked weekly - and the reason why it is not 100% is due to specific cuts that are made to exclude a background contamination. This, of course, might make the signal yield dependent on subtleties of the shape of the PMT response (the cuts are made on signal shape form factors), but I see no reason to doubt that the stability is well under control, although extraordinary claims require extraordinary evidence, and the latter implies going after the subtlest of possible non-exotic explanations.

One thing I would have done if I had designed the experiment myself would have been to prepare a mock-up of the active region, wrap it with black paper, and instrument with similar photomultipliers and the accessory set-up, the overpressure, the temperature controls. This would have allowed to have a real-time comparison between PMT counts from the real NaI detector and PMT counts in a fake one. It would dismiss any claim that PMTs are varying their response seasonally without appeal, but unfortunately we do not have such luxury available in the DAMA-LIBRA setup.

So the question remains. If the signal is strong and significant, and if it is not due to instrumental nuisances -I am sure about the former, less so about the latter- what is its source ? Can we get a model of dark matter particles which produce a similar flux ? It should not be too difficult. Maybe the ball is in the theorists’ court in fact. As for me, I keep cool. I still think there is no new particles to be found with these cunning but a bit overoptimistic endeavours.

Here follows a summary of the talk by Gary Steigman at the Neutrino Oscillations 2008 conference I am attending in Venice. Due to a chronic shortage of time, I will not attempt at reorganizing my notes in a coherent way -apologies if the text is obscure: the lack of corresponding figures and graphs, which Gary used in his talk, cannot unfortunately be substituted by argute explanations on my part. I therefore advise readers with no background in basic cosmology to jolly well skip this post and read something else. On the other hand, insiders will find here no really new information… So this post is essentially just for my own record! I will add pictures if I find the slides on the web, if not… Too bad.

Gary started by noting that in our attempts at understanding the evolution of the Universe, evidence of large scale structures allows us to study times from a few minutes after the big bang to about ten billion years after it. The evolution can be divided by three important moments.

When the Universe is a tenth of a second old, neutrinos decouple from matter. This transition, as the others, is not sharp: neutrinos continue to interact at this time but at a time scale which is becoming long with respect to the age of the Universe. A few minutes later, elements begin to form. Nuclear reactions continue to happen but there is primordial nucleosynthesis only when the Universe is a few minutes old. Finally, about 400 thousand years later, electrons combine with protons to form neutral atoms, and then is when relic photons are free, and they can propagate all the way to us.

So we have Big Bang Nucleosynthesis (BBN, 20 minutes after the big bang), the Cosmic Microwave Background (400 kiloyears after BB), and the Large Scale Structure of the Universe (10 gigayears after BB). They are all complementary probes of the early evolution of the Universe.

The question to ask oneself according to Steigman is whether the predictions and observations of baryon density and expansion rate agree at these different epochs.

The early hot and dense universe during part of its evolution is a cosmic nuclear reactor. As the universe expands, BBN begins when the temperature is of about 70 keV, when the ratio between neutron and proton abundances is . The ratio is crucial for helium abundance. Nucleosynthesis begins but very quickly ends, because the temperature drops and there are coulomb barriers between charged nuclei, neutrons get used up also because of beta decay, and at T =30 keV, 24 minutes after the start, nucleosynthesis ends.

When we talk about the baryon density we mean the nucleon density. But as the universe expands, the density changes. A parameter which remains invariant is the ratio , between nucleon and photon number densities. is of course very small, so is defined as the same number, 10 billion times larger. In terms of and h, the hubble parameter, we can write $\latex eta_{10} = 274 \Omega_B h^2$.

One of the key elements produced in the early universe is Deuterium. The abundance is maximum at about 300 seconds. There is none before 100 seconds. Then it burns to Tritium to end up into Helium four, and it decreases. When the universe is about 1000 seconds old the relative abundance D/H stops changing. This ratio depends on . More nucleon density means less Deuterium produced. So Deuterium is a baryometer: it measures the density of baryons. As the Universe evolves, D is destroyed. Anywhere, the relative abundance of Deuterium is smaller than its plateau value: its evolution is monotonic since the big bang. It can only decrease.

The predicted value of the D/H ratio is sensitive to the baryon density: a 10% determination of D abundance brings to a 6% determination of the baryion to photon abundance.

The way we observe deuterium is in absorption in light sources, high-redshifted quasi-stellar objects. H-I and D-I lines are seen in absorption, but their spectra are identical. An isotope shift is completely equivalent to a velocity shift, so we have to be very careful in interpreting it. An unresolved velocity structure in the measured object causes errors in N(H-I). We need to measure the heavy elements to determine the velocity structure.

Data on D/H can be plotted against metallicity -the ratio of heavy to light elements, such as the relative abundance of Silicon and Hydrogen, Si/H: a measure of heavy element abundance. We only have six data points from background sources at various (small) values of metallicity, and we have to understand well their velocity structure. The points show a lot of dispersion in D/H, and it is hard to see a clear plateau at low metallicity. However, we can fit , taking the dispersion around the mean as the uncertainty. We thus find a 10% error in deuterium abundance. We can use that to measure as , or 6% uncertainty.

The evolution of the Helium 4 mass fraction is represented by astronomers as . It evolves starting from 200 seconds. It increases up to 0.25 at 300 seconds and then it plateaus. Helium 4 starts after deuterium starts burning. Then all neutrons are quickly used up, and we get a plateau. With a neutron to proton ration of 1/7 when nucleosynthesis begins, is 0.25 with very little spread. So helium abundance is insensitive on the value of , but it depends crucially on the competition between the weak interaction rates, charged-current weak interactions, and the expansion rate of the Universe: so Helium abundance can provide constraints of the expansion rate of the early Universe.

The expansion rate is usually defined in terms of the Hubble parameter H, which provides a probe of non-standard Physics. There are many models where H deviates from SM values. The ratio of the square of H to the SM value provides an estimate of the energy density of relativistic particles to the Standard Model expectation, with three families of light neutrinos. Anything that changes that picture causes a deviation. An expansion rate parameter S measures the deviation . There can be many reasons why S departs from 1. parameterizes deviations as . Higher dimensions like those in the Randall-Sundrum model cause a difference in S. S also measures the difference of the gravitational constant from todays value.

We can determine from Helium abundance and we find $Y_P = 0.24 \pm 0.006$.
As a function of the oxygen to hydrogen abundance one can determine Y. Systems with about give a linear extrapolation to zero oxygen abundance, and one finds the value . Alternatively, instead than using 90 data points with uncertainty dominated by systematics, there are other analyses more careful with systematics, where the trend with metallicity is seen better. Any helium one sees is greater than the primordial value, so an upper bound can be extracted from the data, and is found at .

From standard big bang nucleosynthesis there is the prediction is . There is consistency. The deuterium and helium observations plotted together, and S can be seen as a function of and . The helium abundance depends on the expansion factor, while the deuterium abundance also depends slightly on expansion rate factor S. Putting these together we find that there is a consistent, not unexpected, possibility of explaining everything with . 2-sigma away from the standard value of three neutrinos.

In the vs $\eta_{10}$ plane, one has a nice contour plot from V-Simha and G.S. We are consistent with 3 neutrinos. In particular, the BBN constraint from He-4 shows very clearly that in the early universe at least one was present in the early Universe. At more than 2-sigma, there was at least one of them. Also, 4 flavors of neutrino from BBN are excluded.

About lithium, it is produced in the BB in low abundance, in the form of . There is a gap at mass 5, very hard to jump in nucleosynthesis, but there are some reactions that take you up to mass seven. But it stops there: only light elements are formed in the early Universe. From standard BB nucleosynthesis, the prediction of LI abundance is off. As a function of the ratio between iron and hydrogen abundance , one finds values a factor of three lower. Question, should we see a plateau, a speed plateau at low metallicity ? If there is a plateau, we can arbitrarily determine it by drawing a line through data points, and find Li abundance at There is too little lithium according to measurements.

On the CMB radiation, there is a complementary probe. The temperature fluctuation spectrum provides a constraint on the baryon density. Different curves can be drawn on the temperature fluctuation measured for the cosmic microwave background, corresponding to different values of the abundance ratio at 4.5, 6.1, 7.5. This allows to illustrate that it is possible for the data to discriminate the baryon density: so one has an early Universe baryometer which is better than deuterium. One finds , which has an uncertainty a factor two better than what we can get with deuterium abundance. In fact if we superpose them, we find excellent agreement.

If one puts the CMB results together with the BBN results, they overlap well, and taking the CMB values of baryon density and , and use BBN to predict abundances, one finds good matches in , , while no good agreement on lithium abundance.

What are the consequences of the good agreement of physics at 20 minutes and 400,000 year times ? Entropy conservation: the number of photons described by CMB and BBN we find . The ratio in the number of photons is one unless there is entropy creation in between. One can place upper limits on entropy production then.

A modified radiation density for a late decay of a massive particle also give different abundances at the two time scales, and one finds constraints on it too. For variations in the gravitational constant, one can interpret the expansion parameter in terms of G, and comparing the BBN value with the present value one finds values consistent with one.

I received this morning the poster of a workshop on Dark Matter searches at the LHC, which will be held in my University on April 22nd. This is a single afternoon of talks addressed to students of Physics, to educate them on the connection between particle physics and cosmology in view of the start of the collider this fall. Upon glancing at it, I immediately sensed the subliminal message it sends to whomever has been reached by the headlines on the recent lawsuit concerning the risk of black hole creation in the high-energy proton-proton collisions… Here is the poster:

The galaxy has of course nothing to do with an expanding black hole, but it still sends a sinister message. Let me say it here again: black holes will NOT be created at LHC. Scientists cannot even assess the chance of that happening, because the probability that 1) Large extra-dimensions exist in nature, 2) the scale of quantum gravity being both fine-tuned to allow black holes to be produced by LHC and not by past colliders, and orders of magnitude smaller than what it is most reasonable to conceive, is too small to be investigated meaningfully.

In any case, even if microscopic black holes were created at LHC, they would evaporate instantly, due to a phenomenon, Hawking radiation, which only rests on general relativity and quantum gravity, and is thus on much more solid ground than the very production of black holes. And in any case, even if black holes were created and they did not evaporate, they would escape the Earth without more than a few nuclear interactions. And in any case, even if scientists were wrong on all the previous counts, collisions like the ones LHC will produce are generated everywhere by cosmic rays, so the black holes generated inside the LHC would be nothing new under the sun.

For a more meaningful discussion of these issues, please visit this instructive post at backreaction.

Just a note to post here the permanent link to the proceedings of a conference I attended in Corfu (Greece) three years ago. This is a long (32 pages) report on “High- Physics: from the Tevatron to the LHC“, now published in the Journal of Physics: Conference Series [Tommaso Dorigo 2006 J. Phys.: Conf. Ser. 53 163-194]. I think I did post a draft of the paper on this blog a couple of years ago, but then I forgot to post the final version as well.

The paper is a bit dated in some parts, where the most recent (back then) results from the Tevatron are discussed; however, some parts -especially a discussion of the usefulness of Tevatron data for LHC physics- are still readable IMHO. Also worth noting is the fact that the acknowledgments section mentions the late Riqie Arneberg, a friend who passed away last fall, who had accepted the offer I had made to all readers of this blog to proofread the manuscript, and contributed in several places to the clarity of the text.

The publisher has now made available online all its 100 open access volumes through the JPCS home page. Of course I salute this contribution to the free diffusion of science with enthusiasm.

I am subscribed to several discussion groups in the Internet, and my mail box is usually stuffed with messages I do not need. However, just every so often a message worth reading - and passing on - appears. It is the case of the following, which I am glad to paste below. It is a message from George Gliba (gliba@milkyway.gsfc.nasa.gov)

Fellow Observers,

So, were you watching Bootes last night ? If you saw a star lit up and then fade away, you might as well send a note to George… Chances are you would be contributing to our still sketchy knowledge on these fantastically energetic explosions.

This just in - I have been notified by the head of the CDF speakers committee that I have been accepted to represent CDF at PPC08 - a conference on the interconnection between Particle Physics and Cosmology to be held in Albuquerque, NM between May 19 and 23.

In retrospect, my last posting about WIMPs was a good idea - it demonstrates my interest in the matters that I will hear about at the conference.

I also have to report a funny incident. Upon reading the e-mail, I went in search of the web site of the conference, and -by googling for “PPC08″ - I found this other cosmology conference instead. I was slightly bewildered at the beginning, because I did not remember having applied for a conference in St Petersburg, and moreover in time clash with the CMS week of June 23rd -already marked in my agenda. But then I shrugged my shoulders - a CDF talk is always a great honor for me, and I would certainly never refuse the occasion.

Upon visiting the site of the PPC08 conference I noticed that the program had nothing to do with particle physics, though. Now, where was my talk going to go in the list of sessions, ranging from “Large scale structure of the Universe” to “Evolution of Galaxies” to “Cosmological models and crucial observational tests”? Admittedly all highly interesting stuff, but all talks had names attached, and none was on particle physics…

It took me about ten crazy minutes to figure out I had put too much confidence in google this one time. Luckily, the program of the Albuquerque conference is no less interesting (speaking from what I read in the poster), although St Petersburg would have been worth the visit.

It remains to be seen how I will structure my talk. It is tentatively named ”Recent Results from CDF“, and I intend to stick to what the title promises: there are so many new results to show, it will be a real pleasure to pick la creme de la creme…

It was sky transparency. We had suspected that Casera Razzo, the site I occasionally visit with a few amateur astronomer buddies in our deep-sky observing sessions, had the potential to offer a very dark, almost perfect sky; but only once in our dozen visits we had experienced it, while in all other cases the sky had been dark but had left something wanting.

We suspected that the factor that had been adverse in most cases was the transparency of the sky, but we needed some confirmation - after all, there are indeed many possible causes for a light-polluted atmosphere, some of them due to human activity and some others due to atmospheric conditions. Yesterday we reached the same level of quality of our formerly best night at the site - April 14th, 2007-, and we convinced ourselves that light scattered by particles and humidity in the atmosphere is a major factor affecting the darkness of the night in the eastern Alps. Light from towns 50 km away is masked well by the mountains surrounding the site, but the atmosphere needs to be transparent above your head if you want to avoid the photons from those far-away sodium lamps to bounce back  there and hit you.

Mauro’s sky quality meter -a calibrated exposimeter yielding a reading of the sky’s visual magnitude per squared arcsecond - started off at 21.42 at 10.50PM, and as lights in nearby towns were turned off it consistently grew to reach a 21.58 reading at 2AM yesterday night. The latter reading corresponds to a “Bortle-2″ sky - just one notch below the best possible sky, which corresponds to readings of 21.9 or 22.0. Of course, those 0.4 mags of difference mean a whole lot when one observes faint galaxies visually, but 21.6 is probably the best one can hope for on italian territory. Better values can probably be found only far, far away from northern Italy; even professional sites do not often go above 21.6: for instance,  it is a typical reading at sites such as the Roque de los Muchachos, at La Palma - where several observatories are located. See for instance the following plot, taken from the site of the observatorio:

In the plot you see that the V-band magnitude (y axis) reaches 21.5 at zenith on a typical night. The x axis shows the azimuthal direction where the measurement is made, and the different curves refer to different altitudes in degrees. 

So, what did we see yesterday night ? Well, a lot indeed. The temperature went from minus 5 to minus 11 degrees during the four hours of observation, and the wind was almost absent -I had feared it a lot before arriving there. However, the fact that the temperature did not stay constant prevented the mirror of the telescope to reach thermal equilibrium, and this affected the resolution quite a bit, and with it our possibility to push the magnification. For that reason, we mainly observed extended objects at 120x or 200x. Indeed, we were naturally led to spending most of our time on the real showpieces of the winter sky, which -when observed under truly dark skies- show picture-like detail with a 16″ scope. So, little time was spent on the faintest objects, which are usually small and require magnifications in excess of 400x.

A list of observed objects is a rather dry way for a description of the night. Rather, I only mention what really impressed me. Messier 51, the whirlpool galaxy, was one object on which we spent several minutes. It showed filamentary detail inside the main spiral arms, and was a really glorious sight - you felt you could pick it up by one arm, peeling it off the eyepiece lens as you would remove a dead insect from your windshield. And Messier 101, another face-on spiral galaxy in Ursa Major, did not pale in comparison: it showed several H-II regions in the arms, and the details in its structure were the best I ever saw on this object.

M101 is an extended object - covering almost a fourth of a squared degree of sky - and light pollution can make it utterly invisible even with large instruments! In fact, one often sees threads on popular amateur astronomy forums where it is discussed whether M101 is visually observable at all… Quite ironic: under dark skies this galaxy is a true beauty. The picture below (taken by italian amateurs from Verona) represents a good approximation of what was visible through the eyepiece. It is sights like these that keep me wanting for more nights out, hands and feet freezing and nothing else around but snow and silence.

In a few minutes I will be leaving to Casera Razzo with two buddies, a large dobson telescope, and lots of warm clothes. The weather is clear, and we expect a rich observing session, with UMA and LEO starting to show their bounty of galaxies high in the night sky.

The temperature should not dip below minus ten Celsius - or so I gather from the local forecasts. Instead, wind might turn out to be a problem - despite my dobson has a robust mount, a 10 mph breeze is enough to make high-power observations painful, and leave alone the wind chill effect during the night at 1700 meters above sea level, with only snow around. The gradient in pressure between balcans and alps could make things hard for us.

Nonetheless, I have already put together a list of objects I wish to watch with some detail. Among them, several galaxies of course. M51 (aka the whirlpool), the most photogenic interacting pair of the whole sky; M101, a wonderful spiral which usually cannot be observed well - it requires very dark skies to see its spiral arms; and then M106, M65-M66, … the list is very long and thick with showpieces, but also with less-known galaxies. If wind is a problem for chill and stability of the scope, it will indeed help the sky transparency, and I expect we will have a fair chance of exceeding previous records as far as dim details on deep-sky objects are concerned. Wish us good luck… A night of observations during winter time is not too different from a sport performance: you drive two hours, unload the material, mount everything, observe for four-five hours, and then put back things in the car and leave. Not for the faint hearted.