## LHC Starts Collisions; and a Radio Interview Tonight

In the long and careful process of restarting the Large Hadron Collider [LHC] after its two-year nap for upgrades and repairs, another milestone has been reached: protons have once again collided inside the LHC’s experimental detectors (named ATLAS, CMS, LHCb and ALICE). This is good news, but don’t get excited yet. It’s just one small step. … Read more

## More Examples of Possible Unexpected Higgs Decays

As I explained on Tuesday, I’m currently writing articles for this website that summarize the results of a study, on which I’m one of thirteen co-authors, of various types of decays that the newly-discovered Higgs particle might exhibit, with a focus on measurements that could be done now with 2011-2012 Large Hadron Collider [LHC] data, … Read more

## Unexpected Decays of the Higgs Particle: What We Found

A few weeks ago, I reported on the completion of a large project, with which I’ve been personally involved, to investigate how particle physicists at the Large Hadron Collider [LHC] could be searching, not only in the future but even right now, for possible “Exotic Decays” of the newly-discovered Higgs particle .

By the term “exotic decays” (also called “non-Standard-Model [non-SM] Decays”), we mean “decays of this particle that are not expected to occur unless there’s something missing from the Standard Model (the set of equations we use to describe the known elementary particles and forces and the simplest possible type of Higgs field and its particle).”  I’ve written extensively on this website about this possibility (see herehere,  hereherehereherehere and here), though mostly in general terms. In our recent paper on Exotic Decays, we have gone into nitty-gritty detail… the sort of detail only an expert could love.  This week I’m splitting the difference, providing a detailed and semi-technical overview of the results of our work.  This includes organized lists of some of the decays we’re most likely to run across, and suggestions regarding the ones most promising to look for (which aren’t always the most common ones.)

Before I begin, let me again mention the twelve young physicists who were co-authors on this work, all of whom are pre-tenure and several of whom are still not professors yet.  [ When New Scientist reported on our work, they unfortunately didn’t even mention, much less list, my co-authors.] They are (in alphabetical order): David Curtin, Rouven Essig, Stefania Gori, Prerit Jaiswal, Andrey Katz, Tao Liu, Zhen Liu, David McKeen, Jessie Shelton, Ze’ev Surujon, Brock Tweedie, and Yi-Ming Zhong.

## Visiting the University of Maryland

Along with two senior postdocs (Andrey Katz of Harvard and Nathaniel Craig of Rutgers) I’ve been visiting the University of Maryland all week, taking advantage of end-of-academic-term slowdowns to spend a few days just thinking hard, with some very bright and creative colleagues, about the implications of what we have discovered (a Higgs particle of … Read more

## What’s the Status of the LHC Search for Supersymmetry?

It’s been quite a while (for good reason, as you’ll see) since I gave you a status update on the search for supersymmetry, one of several speculative ideas for what might lie beyond the known particles and forces.  Specifically, supersymmetry is one option (the most popular and most reviled, perhaps, but hardly the only one) for what might … Read more

## Quantum Field Theory, String Theory, and Predictions (Part 7)

Appropriate for Advanced Non-Experts

[This is the seventh post in a series that begins here.]

In the last post in this series, I pointed out that there’s a lot about quantum field theory [the general case] that we don’t understand.  In particular there are many specific quantum field theories whose behavior we cannot calculate, and others whose existence we’re only partly sure of, since we can’t even write down equations for them. And I concluded with the remark that part of the reason we know about this last case is due to “supersymmetry”.

What’s the role of supersymmetry here? Most of the time you read about supersymmetry in the press, and on this website, it’s about the possible role of supersymmetry in addressing the naturalness problem of the Standard Model [which overlaps with and is almost identical to the hierarchy problem.] But actually (and I speak from personal experience here) one of the most powerful uses of supersymmetry has nothing to do with the naturalness problem at all.

The point is that quantum field theories that have supersymmetry are mathematically simpler than those that don’t. For certain physical questions — not all questions, by any means, but for some of the most interesting ones — it is sometimes possible to solve their equations exactly. And this makes it possible to learn far more about these quantum field theories than about their non-supersymmetric cousins.

Who cares? you might ask. Since supersymmetry isn’t part of the real world in our experiments, it seems of no use to study supersymmetric quantum field theories.

But that view would be deeply naive. It’s naive for three reasons.

## Off to Illinois’s National Labs For a Week of Presentations

I have two very different presentations to give this week, on two very similar topics. First I’m going to the LHC Physics Center [LPC], located at the Fermilab National Accelerator Laboratory, host of the now-defunct Tevatron accelerator, the predecessor to the Large Hadron Collider [LHC]. The LPC is the local hub for the United States … Read more

## Did the LHC Just Rule Out String Theory?!

Over the weekend, someone said to me, breathlessly, that they’d read that “Results from the Large Hadron Collider [LHC] have blown string theory out of the water.”

Good Heavens! I replied. Who fed you that line of rubbish?!

Well, I’m not sure how this silliness got started, but it’s completely wrong. Just in case some of you or your friends have heard the same thing, let me explain why it’s wrong.

First, a distinction — one that is rarely made, especially by the more rabid bloggers, both those who are string lovers and those that are string haters. [Both types mystify me.] String theory has several applications, and you need to keep them straight. Let me mention two.

1. Application number 1: this is the one you’ve heard about. String theory is a candidate (and only a candidate) for a “theory of everything” — a silly term, if you ask me, for what it really means is “a theory of all of nature’s particles, forces and space-time”. It’s not a theory of genetics or a theory of cooking or a theory of how to write a good blog post. But it’s still a pretty cool thing. This is the theory (i.e. a set of consistent equations and methods that describes relativistic quantum strings) that’s supposed to explain quantum gravity and all of particle physics, and if it succeeded, that would be fantastic.
2. Application number 2: String theory can serve as a tool. You can use its mathematics, and/or the physical insights that you can gain by thinking about and calculating how strings behave, to solve or partially solve problems in other subjects. (Here’s an example.) These subjects include quantum field theory and advanced mathematics, and if you work in these areas, you may really not care much about application number 1. Even if application number 1 were ruled out by data, we’d still continue to use string theory as a tool. Consider this: if you grew up learning that a hammer was a religious idol to be worshipped, and later you decided you didn’t believe that anymore, would you throw out all your hammers? No. They’re still useful even if you don’t worship them.

BUT: today we are talking about Application Number 1: string theory as a candidate theory of all particles, etc.