SUSY en el LHC, Cuerdas sin SUSY y lo que todo físico debería saber sobre Cuerdas

Hace poco encontré estos vídeos sobre supersimetría y teoría de cuerdas, dos temas íntimamente relacionados:

Supersimetría: el LHC regresa a la búsqueda de nueva física
Este vídeo está dirigido al público en general. La anfitriona entrevista a varios físicos, entre ellos a John Ellis, quien habla acerca del Run II del LHC y en particular sobre la búsqueda de nueva física y supersimetría. La explicación a nivel divulgativo es la usual, pero las entrevistas son interesantes y se presenta también el lado más escéptico de la propuesta de SUSY con Alvaro De Rújula que bromea un poco sobre viajar al pasado.

Entre otras cosas, si no se encuentra SUSY en el Run II del LHC, John Ellis señala que tendrá que limpiar su oficina.

El escritorio de John Ellis @CERN

Teoría de cuerdas en un universo sin supersimetría
Luego del Run I del LHC, los medios y "algunos físicos" comenzaron a decir que SUSY estaba muerto. En realidad, y como se explica en el vídeo anterior, SUSY podría estar en cualquier escala de energía y podría incluso ser inalcanzable por el LHC. De cualquier modo esto mete en problemas a muchos teóricos y en particular a los que se dedican a la construcción de modelos realistas de partículas (tipo modelo estándar) a partir de teoría de cuerdas (fenomenología de cuerdas).

Algunos recursos para abordar este tema conceptualmente son:

What if the LHC doesn't see SUSY? en Physics SE
Why string theory implies supersymmetry en The Reference Frame

Saúl Ramos, investigador del IFUNAM, aborda el tema de Cuerdas sin SUSY (y explica exactamente a qué se refiere esto en el tiempo 27:00 gracias a una pregunta) precisamente motivado por el hecho de que no ha habido evidencia alguna de SUSY en el LHC, entre otros.

El squark stop es la superpartícula asociada al top quark y era una de las primeras que se esperaba en el LHC 

La charla no es divulgativa (seminario de Altas Energías en la UNAM) pero es accesible para quien esté interesado sin ser experto. El audio es relativamente malo pero vale la pena intentar seguirlo (como sea se agradece la iniciativa del camarógrafo) y la acción en específico sobre la construcción de N=0 comienza en el tiempo 21:00.


Finalmente, no recuerdo si durante la presentación se cita el artículo en que está basada la presentación, pero parece que es este trabajo:

Non-supersymmetric heterotic model building
Michael Blaszczyk, Stefan Groot Nibbelink, Orestis Loukas, Saúl Ramos-Sánchez

We investigate orbifold and smooth Calabi-Yau compactifications of the non-supersymmetric heterotic SO(16)×SO(16) string. We focus on such Calabi-Yau backgrounds in order to recycle commonly employed techniques, like index theorems and cohomology theory, to determine both the fermionic and bosonic 4D spectra. We argue that the N=0 theory never leads to tachyons on smooth Calabi-Yaus in the large volume approximation. As twisted tachyons may arise on certain singular orbifolds, we conjecture that such tachyonic states are lifted in the full blow-up. We perform model searches on selected orbifold geometries. In particular, we construct an explicit example of a Standard Model-like theory with three generations and a single Higgs field.

Lo que todo físico debería saber sobre teoría de cuerdas
Al fin una charla de Eddie Witten que todos podemos entender... todos los físicos... todos los que conocen, al menos de lejitos, QFT y obviamente relatividad general.

Las diapositivas de la charla están disponibles aquí a través del sitio del Strings 2015.

A groso modo, en la primera parte, Witten comienza con la que sería una formulación 1-dimensional de gravedad cuántica, en la que el tensor de Riemann es idénticamente nulo y así la curvatura de Ricci y la acción de Einstein-Hilbert, con D campos escalares y llega a una teoría de campo en un espaciotiempo D-dimensional curvo. Luego incluso, con este modelo unidimensional, continúa calculando el propagador de una partícula de un punto a otro e introduce interacciones. Finalmente considera el caso dos dimensional, explica por qué Cuerdas es una teoría de gravedad cuántica (no esperen conocer al gravitón, aunque sólo quedan unas patadillas para describirlo) y discute cómo es que en cuerdas desaparecen las divergencias ultravioleta.


Hay además disponible en YouTube una charla de 2013 del mismo Witten llamada Feynman diagrams in String Theory que parece ser esencialmente la misma, aunque quizá con un poco más de detalle (en la primera diapositiva menciona "I will aim to explain the minimum about string perturbation theory that every quantum physicist should know"). Finalmente en algo con relación únicamente a Witten: How does Edward Witten know so much math?.

http://abstrusegoose.com/332

MOOCs and Online Lectures: Supersymmetry, Extra Dimensions and the Higgs Boson

I fortunately happened to live during the rise and development of the internet and other information technologies. Now I'm witnessing the proliferation of the so called MOOCS and open access to (under)graduate level courses, which is great. I'd say these type of courses and lectures are presumably the best option for those who want to self-teach themselves, those who want to change fields of study, or to those who want to deepen their understanding in some particular topic.

I've gone through the whole of David Tong's lectures on QFT (mentioned in earlier posts) and part of his lectures on String Theory too; these are great by themselves and the QFT ones have some advantage in that there are YouTube videos available (though -the videos, not the lectures- of poor quality). It seems that a lot of leading universities and their academics are (becoming?) aware of the relevance of making available good quality content to the general public, even if not specially by well organized MOOCs but just by access to online lecture notes.

Here I share two courses which I'm currently following.

First:

Cambridge Lectures on Supersymmetry and Extra Dimensions
Lectures by: Fernando Quevedo. Notes by: Sven Krippendorf and Oliver Schlotterer

These lectures on supersymmetry and extra dimensions are aimed at finishing undergraduate and beginning postgraduate students with a background in quantum field theory and group theory. Basic knowledge in general relativity might be advantageous for the discussion of extra dimensions. This course was taught as a 24+1 lecture course in Part III of the Mathematical Tripos in recent years. The first six chapters give an introduction to supersymmetry in four spacetime dimensions, they fill about two thirds of the lecture notes and are in principle self-contained. The remaining two chapters are devoted to extra spacetime dimensions which are in the end combined with the concept of supersymmetry. Videos from the course lectured in 2006 can be found online at this http URL.

I've gone until §2.2 and I find the lecture notes really easy to follow. The math notation has some weird spaces in the equations, (which are not numbered btw) and there are some occasional seemingly non-relevant errors, like on page 19,
\begin{equation*}{N_\alpha}^\beta(x_\nu\sigma^\nu)_{\beta\dot\gamma}N_{\dot\alpha}^{*\,\dot\gamma}\stackrel{\color{blue}{?}}{=}{\Lambda_\mu}^{\nu}x_\nu\sigma^\mu\end{equation*} where the $\alpha\dot{\alpha}$ subindices on the RHS are missing; it could've been written simply as $Nx_\rho\sigma^{\rho}N^\dagger={\Lambda_\mu}^{\nu}x_\nu\sigma^\mu$ or, emphasizing the components, I guess the RHS should've been ${\Lambda_\mu}^{\nu}x_\nu(\sigma^\mu)_{\alpha\dot\alpha}$. Also, the procedure to get this equation isn't explicitly -or more carefully- written in the notes (it can be worked out knowing the $x_\mu\sigma^\mu$ transformations under both groups and using the fact that they are the same; the ${\Lambda_\mu}^\nu$ appears as something like ${\Lambda_\mu}^\alpha{\Lambda_\alpha}^\nu$).

I have to say I didn't really liked the video lectures and I didn't find them very helpful: minor issues like the one above don't get straightened and most of the time Prof. Quevedo (which is no insignificant name in the field) just transfer the notes to the blackboard. That's kind of understandable, but, as in the issue I mentioned, not seeing "balanced" indices at an equation should hurt one's eyes enough. However, some discussions may be useful and it is at least more dynamical to follow the notes along with the videos (I also confess that the accent of Prof. Quevedo became a little annoying to me after a while; I don't blame him though, because I might have a similar one).

Then, there's this beautiful course about the Higgs Boson by the University of Edinburgh on what they call Open Education:

The Discovery of the Higgs Boson
Should we be excited about the Higgs boson? Find out more about particle physics and understanding the universe.

Educators: Christos Leonidopoulos and Luigi Del Debbio.

(...)
This free online course introduces the theoretical tools needed to appreciate the discovery, and presents the elementary particles that have been discovered at the tiniest scales ever explored. Beginning with basic concepts in classical mechanics, the story unfolds through relativity and quantum mechanics, describing forces, matter and the unification of theories with an understanding driven by the tools of mathematics.

Narrating the journey through experimental results which led to the discovery in 2012, the course invites you to learn from a team of world-class physicists at Edinburgh University. Learners participate in discussion of the consequences of the Higgs boson, to physics and cosmology, and towards a stronger understanding and new description of the universe.
(...)

The course is meant to be accessible to everyone with high school education. It's already too late to register formally, but there's also a YouTube playlist available from the previous year's course:


So I guess that's pretty much enough ;-) I've seen a few videos and of course there's a lot of detail you won't see, but at least the big picture is there (I didn't truly realize some things, like how to read the plot of the data) and it is fantastic.

I also like to brag a little because most probably I'll be attending the MSc in Mathematical Physics at Edinburgh ;-)

Visualization of the future building of the Higgs Centre for Theoretical Physics at Edinburgh
(due to open in 2016)