## Saturday, November 19, 2011 ... /////

### Profumo di SUSY

Is supersymmetry starting to smell at CERN?

Four phenomenologists have trained their noses. As a result, they recently began to smell

Profumo di SUSY: Suggestive Correlations in the ATLAS and CMS High Jet Multiplicity Data (PDF)
in the winds wafting their way from Geneva.

Tianjun Li, James A. Maxin, Dimitri V. Nanopoulos, and Joel W. Walker (LMNW) have moved their noses closer to some early combined data from both major LHC detectors and what they found was... Profumo di donna, just like in the 1974 Italian movie about a blind Italian captain planning to commit suicide and the Scent of a Woman which translates the Italian phrase to English. ;-)

Just to calm you down, Al Pacino or any other actor starring as the captain finally scrapped the suicide plans. You may guess what was the reason. The title of the movie may help you.

A tango from Scent of a Woman

What about the SUSY phenomenologists who really want to see SUSY at the LHC and they're blind or, to say the least, they still don't see anything clear? Will it be enough for them to smell SUSY? :-) LMNW seem to think it should be enough. Their tone doesn't hide the excitement.

Nanopoulos talking to a Harvard physicist named Weinberg years ago. Nanopoulos may feel less "credible" than Weinberg but I think he's creative, with all the fun papers about strings and the brain function (that I haven't understood so far and I still have doubts whether I ever will).

The experimental side of their arousal depends on the excess multilepton events at the CMS and at the ATLAS (especially those with 9+ leptons in the final state) that have been mentioned on this blog a few times in recent months. The theoretical side of their excitement has a much longer history.

For more than 25 years, Dimitri Nanopoulos was co-authoring papers about flipped SU(5) supersymmetric and stringy models. Note that the papers are sometimes co-authored by John Ellis, one of the three most cited particle physicists ever, and by John Hagelin who would later become the U.S. presidential candidate for the Natural Party and the main high-energy physicist working for the Maharishi Mahesh-Yogi meditation religious movement. ;-)

Because of Hagelin's professional incorporation of string theory, GUT, and unified field theory in general to Maharishi's meditation booklets, I almost started to believe the meditation crap when a couple of Maharishi's Indian disciples came to visit our high school right after the fall of communism two decades ago. :-)

They're clearly colorful characters and I think they are very smart, too. So what is this research direction all about?

The minimal grand unified theory is based on the gauge group $SU(5)$ which contains the Standard Model gauge group $SU(3)\times SU(2) \times U(1)$ as a subgroup. A single fermion generation is encoded in two representations of $SU(5)$, namely in ${\bf 5}$ and $\overline{\bf 10}$. When the group $SU(5)$ is enhanced to $SO(10)$ or an even larger group $E_6$ – which is a natural chain of embeddings in heterotic string theory where even the largest, last group is embedded into a single $E_8$ – the fermions may arise from a single spinor representation of $Spin(10)$, namely ${\bf 16}$, which also contains a right-handed neutrino aside from ${\bf 5} \oplus \overline{\bf 10}$.

Their flipped $SU(5)$ began with this 1987 paper and it was going in a different direction. Instead of a simple $SU(5)$, they work with a "not quite simple" group $SU(5) \times U(1)$. This extension is somewhat similar to what happened in the electroweak theory. People would also initially think that the electroweak interactions could have been produced by a simple $SU(2)$ but at the end, they needed $SU(2)\times U(1)$. Such an addition of a $U(1)$ factor has various desirable consequences and it may be argued to be natural by looking at various stringy vacua.

Before the mid 1990s, such Flipped models would be located in the set of heterotic vacua in the Free Fermionic Formulation, something I was extremely fond of 18 years ago or so: all the world sheet fields that don't carry the vector indices of the large 4-dimensional spacetime are fermionized and one introduces lots of sectors with various mixed periodicities for them and the corresponding GSO conditions. A whole "small landscape" of such models may be constructed and old computers two decades ago would be already playing with such things a lot.

However, since the second superstring revolution, new setups that became even more convincing were born: intersecting brane models and F-theory (a Father theory based on Fibers) named after VaFa who also speaks Farsi. Note how many letters F are Flying around here, taking Fantastically many Forms and Flavors. Now they may be Feeling the Fragrance of the Female Fun named SUSY which Fould be Fery Fortunate.

I don't want to present their whole paper in a blog form because that may be lots of unnecessary work – because you may try to read the actual paper – and I could say some wrong things, too. However, their setup is very interesting and aside from the possible early CMS and ATLAS signals of new physics, they combine some of the advantages that many people who have ever been impressed by string phenomenology must have noticed.

These F-lipped models inspired by F-theory may share the virtues of the old flipped SU(5) models – like solutions to the doublet-triplet splitting problems and other typical technical hurdles one tries to overcome in the grand unified model building. Also, the setup naturally incorporates the no-scale supergravity. Those of us who still believe that supersymmetry is the "first step" towards an explanation of the smallness of the cosmological constant, the no-scale supergravity is a natural second step because the vacuum energy vanishes at least in a leading approximation (at the tree level) and smoothly explains the flatness and longevity of the Universe.

The mass of the gluino, the supersymmetric partner of the gluon, may be as low as 518 GeV in their model (their best fit), without contradicting the (detailed) current LHC bounds. This leads to the mass of 120 GeV for the Higgs boson, my new favorite one, as well as new vector-like particles inspired by F-theory at 3.05 TeV. If this optimized point in their parameter space is essentially right, and it is of course a big If but far from a strictly impossible one, the five inverse femtobarns of collisions that each detector has already recorded should be enough for the discovery of SUSY!

Now, of course, your humble correspondent shouldn't get prematurely carried away, much like in the Maharishi case, and neither should you! But if these optimistic hints have made you smile, it is a totally justifiable reaction. :-) As they say, their model hasn't just passively survived the bounds; it has actively survived them, helping to explain emerging bumps. The model isn't another lamb waiting to be slaughtered by the expanding razor of LHC limits; it is a lioness leading the charge to explain the early LHC observations.

By the way, the word "Profumo" in the title is "fragrance" in Italian but it is also one of three particle physics faculty colleagues of Tom Banks in Santa Cruz. ;-)