Stringy Matters

Two topics dominated the String Phenomenology 2014 conference (StringPheno 2014) held at ICTP from 7 to 11 July 2014: F-theory, one of the more technical topics in string theory, and cosmology, in light of the recently announced BICEP 2 results. Held every year at different locations, the String Phenomenology conference aims to bring together researchers whose main research focus is to connect string theory with particle physics and cosmology.  This year, a time when string phenomenology is at the cusp of some exciting advances, leaders in the field gathered at ICTP to lecture on and discuss about the trending topics in the field.

"String phenomenology is the bridge between the more mathematical aspects and actual data observed at accelerators and observatories," says Luis Ibanez, Universidad Autonoma de Madrid, Spain, who gave an overview lecture at the conference summarizing the talks of this year's StringPheno conference. Mirjam Cvetic, University of Pennsylvania, USA, was one of the speakers whose talk focused on some mathematical aspects of string theory: advances in F-theory. "At this time we are walking hand-in-hand with mathematicians and developing new techniques to connect string theory with particle physics," she says.

In addition to this mathematical facet of string theory, the discussions at the conference were greatly influenced by the release of the BICEP 2 results, the Planck data due to be released soon and the LHC ready to start its scheduled run next year. Ibanez says that the time is right for string phenomenologists to put their tools to test. "I believe string theory is the theory that is best situated to address what the implications of these experimental observations are," he says.

Dieter Lüst, Ludwig Maximilians University of Munich, Germany, agrees. "String theory tries to explain the fundamental laws of nature, and, in my opinion is, so far, the only framework that is developed well enough to address some important questions in particle physics and cosmology," he says.  Lüst's own research interests include "stringy features of generalised geometry", and he gave a talk on double field theory and non-geometric string backgrounds at the conference.  

In keeping with the main aim of StringPheno conferences, talks of the 2014 edition gave participants insights into very specific ways that string phenomenology can be used to understand aspects of particle physics and cosmology.  "There is a lot of really interesting phenomenology that we can inform people about, including our colleagues working on neutrino physics," says theoretical physicist Burt Ovrut, University of Pennsylvania, USA, who is well known in the field for his work on heterotic string theory. Ovrut's talk was on how string theory can provide tools to determine neutrino mass hierarchy. "My guess is that when one starts looking at the regime that the LHC will be looking at when it is switched on, you will see new phenomenology of various kinds, and neutrino mass hierarchy will be just one of them."

One of the speakers who lectured on string cosmology was Hans Peter Nilles, University of Bonn, Germany. String cosmologists are eagerly awaiting the fate of the BICEP 2 results as only a particular class of string inflation models, called large field inflation models, would remain relevant if BICEP 2 results are verified. Nilles' talk focused on one class of such inflationary models, "Axion Monodromy."  "Axion Monodromy is a certain way of having a large field range but in a controlled way. In some way [the field] is like a spiral staircase," he explains. In simple words, the field remains confined in a small circumference,  but as it spirals down it still covers a large distance.

Many of these prominent speakers say that a crucial point for the future of string phenomenology will be the experimental observations of BICEP 2, Planck and LHC. And they all agree these are exciting times for the field. "These times for string phenomenology are like the sixteenth and seventeenth centuries, when the explorers were discovering new lands and charting the world. We [phenomenologists] are charting solutions that string theory can provide," says Ibanez.

More details, lecture notes and talk abstracts are available on the String Phenomenology 2014 website.