Thursday, January 31, 2013

Recommended by us: Backreaction on the Anthropic Principle

Waiting to have more time to tell my experience in Cambridge, MA [January has been crazy: two removals, VISA problems, accommodation searches, etc...] let me just suggest a beautiful post by the Backreaction blog. I enjoyed the reading a lot and I suggest to follow the discussion in the comments.

Saturday, January 19, 2013

Recommended by us: Organizing the masses at MINOS

Organizing the masses at MINOS


By combining its neutrino and antineutrino data sets, 
MINOS  has  provided first constraints on the spectrum 
of neutrino masses (represented by the sign of Δm2), the 
CP-violating phase δ,and whether muon or tau neutrinos 
are more strongly mixed  with the so-called ν3 mass state 
(indicated by θ23). The relative goodness of each scenario
 is given along the vertical axis in terms of a difference of 
log-likelihoods. The parameter Δm2 and the angles θ13 
and θ23 relate to the relative masses of the neutrinos and
to how quantum mechanically "mixed" the three types are.
Over a decade ago the evidence became clear that neutrinos, which come in three varieties, can morph from one type to another as they travel, a phenomenon known as neutrino oscillation. By tallying how often this transformation happens under various conditions—different neutrino energies, different distances of travel—one can tease out a number of fundamental properties of neutrinos, for example, their relative masses. The MINOS collaboration has been doing exactly this by sending an intense beam of muon-type neutrinos from Fermilab to northern Minnesota, where a 5-kiloton detector lies in wait deep underground.

In this new result, MINOS has observed the rare case of muon-type neutrinos changing into electron-type neutrinos. This transformation is governed by a parameter known as θ13, and the MINOS data provide new constraints on θ13 using different experimental techniques than previous measurements. MINOS also collected data with an antineutrino beam, and the real excitement comes in when combining the antineutrino and neutrino data sets. Differences between the rates of this particular oscillation mode between neutrinos and antineutrinos would point to a violation of something called CP symmetry. While physicists know that CP symmetry is violated by quarks, it remains unknown whether the same is true for neutrinos. A new source of CP violation is required to explain why the universe began with more particles than antiparticles, and neutrinos could hold the key. (If the universe began with equal numbers of particles and antiparticles, they would have subsequently annihilated away, leaving nothing left over to make the stars and galaxies we have today.)
                                                                                                       (Continue to read on Fermilab Today)

Sunday, January 13, 2013

SRT (Sardinia Radio Telescope)

Per chi si fosse perso la puntata del nuovo programma di divulgazione scientifica "E se domani", condotta da Massimiliano Ossini e andata in onda ieri 12 Gennaio, dedicata al nuovo radiotelescopio, il Sardinia Radio Telescope (SRT), con interviste a Sergio Poppi e Nichi D'Amicopuò rivedere lo scorcio della puntata a questo link presente nel sito dell'Istituto Nazionale di Astrofisica (INAF)

Fotografia del SRT

Descrizione della puntata di "E se domani" dal sito web della trasmissione
"Nella seconda puntata dalla cosmopolita Milano, Massimiliano Ossini si sposta in un territorio aspro e meraviglioso, la SardegnaRacconta come le viscere di questa terra siano state anche il luogo di straordinarie avventure tecnologiche. Visita Porto Flavia, un incredibile porto minerario scavato nella roccia a venti metri sul mare. Il racconto della Sardegna continua poi fino alla zone delle grotte che oggi sono l’avamposto della ricerca spaziale e si ripercorrono le tappe dell’addestramento per astronauti che sottoterra sperimentano le dure condizioni di vita nello spazio. E infine raggiungiamo il gioiello della scienza italiana costruito al centro dell’isola, uno dei più grandi radiotelescopi d’Europa, una grande parabola che riceve segnali dai confini più lontani dell’universo."

Thursday, January 10, 2013

Recommended by us: Boson



All particles fall into one of two classes, bosons or fermions. Two bosons with identical properties can be in the same place at the same time, but two fermions cannot.
          By Sean Carroll, California Institute of Technology

There are two kinds of elementary particles in the universe: bosons and fermions. Bosons don’t mind sitting on top of each other, sharing the same space. In principle, you could pile an infinite number of bosons into the tiniest bucket. Fermions, on the other hand, don’t share space: only a limited number of fermions would fit into the bucket. Matter, as you might guess, is made of fermions, which stack to form three-dimensional structures. The force fields that bind fermions to each other are made of bosons. Bosons are the glue holding matter together.
Bosons and fermions act like two different kinds of spinning tops. Even when a boson or fermion is by itself, it always has an intrinsic angular momentum, which scientists call spin. Bosons always have an integer amount of spin (0, 1, 2...), while fermions have half-integer spin (1/2, 3/2, 5/2...).  Before July 2012, every fundamental particle that physicists had discovered had non-zero spin. But the theory behind the Higgs boson predicts that it should have no spin. If the early indications hold up and the new particle discovered at the Large Hadron Collider really is the Higgs boson, it will be the first known example of an elementary particle that knows no direction and no polarization—a truly revolutionary discovery. 


Thursday, January 3, 2013

Processi diffusivi, moto browniano e meccanica stocastica

Nota Bene: per la comprensione di questo post è consigliata la lettura del post "Meccanica Quantistica e Meccanica Stocastica" che puoi trovare a questo link.

Meccanica Stocastica

In questo post vorrei descrivere la teoria sviluppata da Edward Nelson chiamata meccanica stocastica. Cercherò di introdurla prima in termini matematici. Poi considererò una sua estensione per mostrare che essa può fornire una soluzione al problema delle “variabili nascoste”.

Edward Nelson
La meccanica consiste di due parti: la dinamica e la cinematica. Supponiamo seguendo Nelson, che si parta dalla meccanica classica e si cambino le specifiche della cinematica, così che i percorsi non siano più differenziabili, ma siano invece dei semplici percorsi di un processo di diffusione.