Survey of vector-like fermion extensions of the Standard Model and their phenomenological implications

April 18, 2014 Comments off

Released on the arXiv today [link]:

S.A.R. Ellis, R.M. Godbole, S. Gopalakrishna, J.D. Wells. Survey of vector-like fermion extensions of the Standard Model and their phenomenological implications

Abstract: With the renewed interest in vector-like fermion extensions of the Standard Model, we present here a study of multiple vector-like theories and their phenomenological implications. Our focus is mostly on minimal flavor conserving theories that couple the vector-like fermions to the SM gauge fields and mix only weakly with SM fermions so as to avoid flavor problems. We present calculations for precision electroweak and vector-like state decays, which are needed to investigate compatibility with currently known data. We investigate the impact of vector-like fermions on Higgs boson production and decay, including loop contributions, in a wide variety of vector-like extensions and their parameter spaces.

Categories: Particle Physics

Completing Hirsch’s h index measuring scholarly impact

April 13, 2014 Comments off

Ranking an individual’s research impact is very hard. Unfortunately that’s what administrators at universities and laboratories worldwide must do. Who should get more pay? Who should get tenure? Who is more impactful in the world of scholarship? It is seemingly impossible, yet we try anyway.

There is a temptation to take somebody’s entire research portfolio and boil it down to one number so that he or she can be ranked more easily with others. One approach is just to count number of papers published, but this makes no sense at all with the rise of “predatory journals”, and the willingness of many otherwise good journals to expand beyond reason to make room for low quality work beside high quality work.

Another number used in the past was total citations to research articles. Or in other words, how many times did somebody else write their own research paper and cite you in it. You are considered better if you have a higher number of citations to the body of your work. However, this isn’t fair to young people who have not been in the field long, and who have not accrued a large number of citations over time despite perhaps being much better than an older researcher.

Another measure to rectify that is average citations per paper. This doesn’t punish the young people as much, because if you have written 5 papers with 200 citations each on average, which makes a total of 1000 citations, it is probably a more impactful career, and a better scholar, than an older colleague who has written 200 papers over decades with only 5 citations each.

However, the problem with citations per paper is that an older person could have written a paper from 30 years ago and get a cagillion citations that accrue every year and not have to do anything more. Their career, and funding, and pay raises, and respect, would be based on interest payments of a good investment decades ago. That is not fair either.

And with this in mind Hirsch introduced [1] the “h index”. A researcher’s h index value is when they have written at least h number of papers with at least h citations for each paper. This is a nice compromise between consistent value and total citations. A researcher can have a huge number of citations accrued from a paper in 1977 but have a small h index.


The h index has taken universities by storm. Everybody wants to know a person’s h index as the most important single number characterizing their research impact. That is not to say that people do not understand the limitations. Some fields are huge with very large numbers of references in each paper, which inflates the h-index. Other fields have a huge number of authors, and get themselves on a quasi-infinite number of papers (high-energy experimentalists), many of which they have barely read. Their h index shoots up all the same.

Even within a subfield you can have vast differences in how easy it is to get citations and increase the h factor. For a while in particle theory if you had the words “ADS/CFT” or “Neutrinos” anywhere in your title, it automatically meant 50-100 citations. If you ambulance chase — meaning you wrote a paper very fast on an experimental anomaly — you often get very large numbers of citations. That is playing out in the cosmology community right now. There is a citations bonanza for all papers discussing the tensor mode fluctuations of the cosmic microwave background radiation perhaps seen by the BICEP2.

But do not get me wrong, I think “piling on” for an interesting theory direction or experimental result is entirely appropriate. Experiments cost many millions or even billions of dollars and when results come they should be payed attention to, and focus should happen. And when an incredible theory discovery like the ADS/CFT correspondence comes along, researchers should squeeze it for everything it’s worth. It is nobody’s fault, and it is not dirty, that citations come from this. Trends in research are healthy to really crush the subfield and get all the meaning out that one can. I get annoyed by people who think that a sure proof of original thinking is that nobody cares or cites the paper. (They usually don’t phrase it that way, but that’s the upshot.)

Anyway, on a recent visit to the University of Michigan Keith Dienes and I were having a dinner time discussion about these matters. In the process he told me some of his very interesting insights regarding the h factor. He recognizes that the h factor as a single number measure of scholarly impact is perhaps better than anything else we have that is widely recognized and understood, but suggested how the h factor’s utility could be greatly improved or “completed” in a conceptually straightforward way. The fundamental observation he made, which is something a good physicist would think of, is that “numbers of papers” and “citations” are different units. The h factor assumes that the conversion between these two units is alway 1, but there are circumstances where that is entirely inappropriate and the h factor then carries no worthwhile meaning. The conversion factor must be calculated for each field, and ideally for each subfield to really measure the impact.

He has been encouraged to write up these thoughts (including by me), since this is such an important consideration at universities these days. Now the paper has appeared on the arXiv [2]. Anybody who is required to think about how impactful researchers are across different fields and even subfields may find it very helpful to read this interesting and insightful paper.

[1] J.E. Hirsch. Proc. Nat. Acad. Sci. 46, 16569 (2005). arXiv:physics/0508025.

[2] K.R. Dienes. Completing h. arXiv:1404.2603.


Categories: Education, Variegations

How university enrollment pressures of the 1930s helped usher in the sexual revolution decades later

April 12, 2014 Comments off

Saturday musings.

I ran across a reference in the New York Times of an interesting book by David Kyvig [1] about daily life in the United States in the 1920s and 1930s. I was curious to see what it said about daily life at American universities during this time. Our excellent library at the University of Michigan had a copy and the book is captivating. 1920s America is one of the most fascinating times in our history, as we transitioned so rapidly from a backwards country to an intellectual, cultural and economic powerhouse. It was a time where freedom of individual expression was flowering, and cultivation of the individual mind was starting to be valued. It is no wonder to me that some of the first greatest physics results from America came in the 1920s. I think of the Davisson-Germer experiment published in 1927 [3] as one of the key scientific discoveries that roughly marks the beginning of top-flight American physics research. This particular result established for the first time that electrons act like waves, and was central to the development of quantum mechanics.

This rapid rise of the American higher educational landscape started in the 1920s, and that is why I was so interested to read about how universities started changing around that time. I learned by reading this book that many more students were graduating from high school than ever before. This put tremendous pressure to expand universities, increase enrollments, and higher more faculty:

“By 1940, half of all eighteen year olds [obtained] a high school diploma, triple the percentage who had done so merely twenty years earlier. The increase in high school graduates together with the growing demand for better-educated teachers helped stimulate a significant rise in college attendance during the 1920s and 1930s. … the overall enrollment … grew from 600,000 to 1.5 million. Most of the enrollment growth involved middle-class students attending non elite public universities in the Midwest and elsewhere.” [1]

The schools in the Midwest were much larger than the east coast “elite” schools, and they also were co-educational, a somewhat new development in the country, as least regarding the magnitude of coeducational instruction.

“Like secondary schools, colleges and universities underwent curricular reform and expansion in the years between the world wars. As the number of faculty tripled, the variety of courses increased proportionally. Courses and programs in business, engineering, fine arts, and education and new approaches to the study of human society such as anthropology, political science, and sociology were added to the traditional arts and sciences, medicine, law, and theology. Courses [were] designed to prepare students for the ordinary routines of everyday life, gradually becoming as straightforward and frank as the popular Indiana University course on marriage begun by Professor Alfred Kinsey in 1938, also entered the catalogue.” [1]

I found it interesting that the big, practical courses that universities so often have now for younger students (freshmen and sophomores) were initiated during the grand expansion of the university curricula in the 1930s. I also did not know that Alfred Kinsey, who is most famous for his scholarly yet bestselling 1948 book “Sexual Behavior in the Human Male”, was one of the leading “star professors” to develop a large enrollment course at Indiana University, as part of this new national trend. I did some searching to see why he did it, and what made it so successful, and here are some passages from Brown and Fee [2] explaining:

“Kinsey was deeply disappointed that he was not offered a professorship at a more prestigious university. Perhaps because of this disappointment, Kinsey made an unusual career move in 1938: he agreed to lead a team-taught course on marriage and the family instituted in response to a student petition. High points of the course were Kinsey’s illustrated lectures on the biology of sexual stimulation, the mechanics of intercourse, and the techniques of contraception, as were his spirited denunciations of repressive laws and social attitudes. … The Indiana students responded enthusiastically, and his course enrollments grew to 400 by 1940” [2].

At the time he was initiating this course, and seeing the tremendous interest of the students in such “practical things” he shifted his research interest just as dramatically. As Brown and Fee tell us, “Kinsey now shifted his research focus as well, transferring his obsessive concern with variation among gall wasps to the varieties of human sexual experience. He required students in his marriage course to have private conferences in which he took their sexual histories. On weekends and vacations, he conducted similar interviews in nearby communities, and later in such cities as Gary, Chicago, St. Louis, and Philadelphia. … In January 1948 [ten years after his course began], Kinsey and his collaborators published Sexual Behavior in the Human Male”[2].

Kinsey’s highly recognized research leads Brown and Fee, and most others, to conclude that he was “one of the most influential Americans of the 20th century” who “helped usher in the ‘sexual revolution’ of the 1960s and 1970s” [2]. Who would have thought in the 1930s that the enrollment pressures at Universities that made it attractive and possible for Kinsey to start his course back then would ultimately influence so many through his blockbuster selling books of the late 1940s and 50s, and help facilitate the rise of the sexual revolution.


[1] David E. Kyvig. Daily Life in the United States, 1920-1939. Westport: Greenwood Press, 2001.

[2] T.M. Brown, E. Fee. Alfred C. Kinsey: A Pioneer of Sex Research. Am J Public Health 93, 896 (2003).

[3] C. Davisson, L.H. Germer. Diffraction of Electrons by a Crystal of Nickel. Physical Review 30, 705 (1927).



Categories: Education

The God Particle and Devil collaborate to give low Bacon-Erdös number

March 15, 2014 Comments off

I was informed last night by a visitor to the University of Michigan — an information theory expert no less! — that my credited participation in Particle Fever has given me a low (i.e., finite) “Bacon number.” Apparently people track through the IMDB database the number of connections via co-stars in films that it takes to reach Kevin Bacon. Here is my path that gives a Bacon number of 4:

James Wells with Leonard Susskind (Particle Fever 2013)
Leonard Susskind with Irvin Kershner (The Nature of Existence 2010)
Irvin Kershner with Illeana Douglas (The Last Temptation of Christ 1988)
Illeana Douglas with Kevin Bacon (Stir of Echoes 1999)

I find it amusing that Particle Fever, a movie largely about the “God Particle” (i.e., the Higgs boson) is connected in my path with the Last Temptation of Christ — a film that gives the devil a central role. All films are pretty heavy, meaning-of-life kind of works.

In the discussion last night I also was told that the highest level of coolness is when you have the lowest Bacon-Erdös number. I’m probably not cool because I didn’t know that. Erdös was a brilliant, prolific, itinerant mathematician who was sort of the Kevin Bacon of mathematics, and it is a mathematician’s playful distraction to count how many co-sets of collaborators you are away from a published paper with him. It turns out that my Erdös number is 3:

James Wells with G.L. Kane in PRL 76, 869 (1995)
G.L. Kane with P.J. Malde in PLB 317, 454 (1993)
P.J. Malde with P. Erdös in J. Graph Theory 13, 353 (1989)

That gives me a total Bacon+Erdös number of 7 (4 Bacon + 3 Erdös), which apparently is quite low.

Interestingly, Natalie Portman also has a Bacon+Erdös number of 7 (2 Bacon + 5 Erdös). If she became a co-author with me and I became a co-star with her we’d both reduce to 6, matching Richard Feynman’s 6 (3+3). I’ll bring it up next time I see her.

stir of echoes

Categories: Variegations

Stanford University president compares American and German students, 1903

February 15, 2014 Comments off

Having spent a lot of time at German universities and American universities, I was amused by a passage written in 1903 by Stanford University’s first President David Starr Jordan.  Qualitatively I think some of what he said in 1903 applies today, although he was surely much too harsh on the German boys. It smacks of resentment that he really thought German boys were better than ours, and he tried hard to find reasons why we might be better, even though as a University president I’m sure he wished Americans were more academically inclined.

Also, I wonder if in 1903 it was the same as today, that American students and American education has a significantly higher variance than students and education in Germany. This is widely recognized today, but Jordan doesn’t mention that.  I suspect that it was the case back then also — think Little House on the Prairie schoolhouses versus fancy New England Prep Schools. And the quip about American westerners being more broadly knowledgeable about practical things of the world still holds true today I think. In my extended family, Western Americans can change plumbing, build a deck, and replace a muffler, but Easterners have to call somebody when the refrigerator light goes out.

Here’s the passage:

“It is true that in the gymnasium [academic track German preparatory high school] students get on faster than in our high schools and preparatory schools. The German student is as far along in his studies at sixteen as the American at eighteen. This is due to the fact that American life makes more outside demands on boys than life in Germany does. The American boy is farther along in self-reliance and in knowledge of the world at sixteen than the German at twenty. The American college freshman, especially if brought up in the West, knows a thousand things, outside of his books and more useful, because more true than most of what his books contain. He can ride, drive, swim, row, hunt, take care of horses, play games, run an engine, or attend to some form of business, while the German boy cannot even black his own shoes.”

- David Starr Jordan. The voice of the scholar, with other addresses on the problems of higher education. San Francisco: Paul Elder & Co, 1903

German boy on his first day of class with his Schultüte.

Categories: Education

A student petitions his professor, Russia 1899

February 9, 2014 Comments off

One of the things that literature can do that is hard to replicate otherwise is to give a boots-on-the-ground feel for what life was like in a different era. Being a professor, I am especially interested in what university life was like at different times and in different places.

For Christmas I was given Anton Chekhov’s fascinating 1899 first-person novella “The Dreary Story” about a distinguished professor of medicine, Nikolay Stepanovitch, reflecting on his life, and recounting the daily banalities near the end of his career. He chronicles his interactions with colleagues, his preparation and delivery of lectures, his thoughts on the value of education, his thoughts about who will become great researchers and who will not and why, and thoughts about students. It is a fascinating read for anybody involved in education, both students and teachers.

Chekhov was a physician by training, and was not many years removed from his schooling when he wrote this novella just shy of his 30th birthday. He also was a tutor for some time, and so had close contact with a multitude of students’s abilities, ambitions and life stories. The acuteness of Chekhov’s observations combined with his recent close connection to higher education adds interest for me in this story.

There is one section that is particularly interesting with regard to student interactions with the professor. It reports of a “sanguine youth” visiting Professor Stepanovitch during office hours, asking to be passed on an examination. Professor Stepanovitch denies the student a passing grade, and during the recounting of this appeal reveals to the reader his unflattering thoughts about the student: he is more interested in beer than thinking, has no real commitment to medicine, lies on the couch most of the day, and could tell you much more about “the opera, about his affairs of the heart, and about comrades he likes” than about his studies. There are any number of modern-day unproductive diversions for students that could substitute for what Chekhov meant by “opera”, such as following sports, pop stars, reality shows, movies, and other activities that have very little lasting value for the individual and present a huge opportunity cost when pursued to excess.  Professor Stepanovitch’s thoughts fit well with what gives today’s professors concerns about some current students.

There is a moment when the student tries to give his “word of honour” that if he is given a passing score he will ___, but the student never finishes the thought, because Professor Stepanovitch has already waived his hands and sat down, signaling to the student that he has heard it before and he will not buy whatever the student is about to say. And what could the student have said? There are not many options. Perhaps the student is wishing to say, “I will keep learning it over time and will make sure that it never hurts my ability to practice good medicine. Just pass me on this last hurdle, and I will be on my way and make you proud. You’ll see. I promise.”

The professor will have none of that. It is often a young person’s fundamental confusion to believe that it is convincing to say “give me this thing I really want, and then I promise to do something good”, whereas life really works mainly in the other direction, “do something good, and then you will get something more.” Professor Stepanovitch ends his recounting of the office visit with a devastating unspoken send-off to the student: “Peace be to thy ashes, honest toiler.” He counts the student among the living dead, who will never understand and will never amount to anything.

It is a cynical story but presumably evokes well what Chekhov understood and saw in late 19th century Russia. So for all you students out there, if you eagerly sat through ESPN’s full coverage of “signing day” for college football, or if you are keeping up with the Kardashians, and you compromised success in the classroom in any way because of it, remember what Professor Stepanovitch would say,”Peace be to thy ashes.”

On the other hand, this story is from the perspective of a professor, who values, or at least has been conditioned over time to value, intellectual pursuits and academic success above anything else. There are more paths to a successful life than Professor Stepanovitch is able to admit, but he is surely correct that an imbalance of beer, “opera”, football, Kardashians, etc., are not compatible with the pursuits of higher academics or of intellectually intensive professions such as medicine. Young people have to choose.

Photo of Anton Chekhov

Categories: Education

In praise of theory and speculation, with help from John Steinbeck

February 2, 2014 Comments off

I once heard a famous and well decorated experimental physicist say that experimentalists simply shouldn’t listen to theorists at all. Experimentalists should just measure and things will come what will, and they should pay no attention to theorists speculations and arguments at all when deciding what experiments to do.

I was very young and inexperienced at the time, but thought then as I do now that it was a dangerous and silly philosophy. There are so many examples of how it pays for communication to go both ways, theorists paying close attention to what experimentalists say and experimentalists paying close attention to what theorists say.

An example that I was reminded of recently is of an experimental collaboration that was building up steam to look for invisible orthopositronium decays. One argument was that the electron and positron could annihilate into extra dimensions. However, Friedland and Giannotti (arXiv:0709.2164) showed that such decays would be disastrous to supernova cooling rates, and that the proposed experiment was guaranteed to not find anything. In other words, a waste of time and money, and a huge opportunity cost to the experimentalists involved. The anti-theory philosophy would say, “Don’t listen to those theorists! Just do it! Measure what you can and want to measure!” which would be clearly bad advice here. If there were infinite numbers of people and dollars, that might not do harm (I doubt it then too), but in the present world, it is more prudent to pursue our best bets, guided by theory.

Regarding best bets, it should be noted that the Higgs boson was pure speculation until it was discovered recently. It was, gasp, just a theory model! It had no direct experimental support, and alternative theories without the Higgs boson abounded. Yet, luckily, there were experimentalists who sorted through the alternatives to decide on a best bet, with theory guidance, and then designed fantastic detectors and experiments and search algorithms focussed on finding it. Without that sustained dedication to this speculation they would not have succeeded.

And anyway, theory and speculations are what give joy to intellectual pursuits. Theory haters are unhappy people, and happy people are more productive, so unleash your speculations and theories. If you won’t listen to me, here’s encouragement from John Steinbeck:

“There are some people who deeply and basically dislike theories and are hostile to speculations. These are usually unsure people who, whirling in uncertainties, try to steady themselves by grabbing and tightly holding on to facts. … Speculation or theory-making on the other hand is simply a little game of pattern-making of the mind. The theory hater cannot believe that is important. To such a person a theory is a lie until it is proven and then it becomes a truth or a fact. But there’s no joy in it.”


Categories: Particle Physics

The year I was married to Susan Sontag

January 26, 2014 Comments off

Some time ago, shortly after starting a postdoctoral research position at CERN in Geneva, I was offered an Assistant Professorship at UC Davis. My family and I decided to go, and so we scurried out of Europe for California.

When you move from U.S. to Europe and then back within a year’s time, you tend to have many things displaced. Here I was staring at my office in Davis with nothing to put in it: no books, no periodic table posters, no pictures of Albert Einstein, and no pictures of my family.

So, I went to a newsstand and bought a magazine with lots of pictures in it, cut out the first good picture I could find, stuck it into a frame I just bought at Walmart, and hung it on my wall.

The picture was of a woman with long flowing black hair, holding a cigarette in her right hand and resting her left hand on a stack of papers scattered across her park-bench desk. An old black rotary phone sat out of reach at the edge of the table facing away from the subject, as though she knew it was temptation that had to be suppressed. On the wall hung a poster of a typewriter rushing past a train on railroad tracks, with the title “la rapidissima. Olivetti”. I was proud of my emergency picture on the wall.


Within a week of hanging the picture I noticed everyone’s eyes drawn to it as they walked into my office. Most people didn’t say anything, but just stared, instinctively knowing that there was something special about the woman. Only a few would ask, “That your wife?” and I would have to explain. In time, I came to realize that most visitors that had come to my office over that year thought she was my wife.

I became intrigued to find out who my “wife” really was. I learned her name, Susan Sontag. I learned that she was one of the greatest “public intellectuals” our country has known. She refused university appointments, and the security that would come with it, despite surely being able to get any named professorship at any university she would like. I learned that she was a voracious reader. Larry McMurtry, a famous voracious reader himself, once remarked that she is the only person he has met who he is sure has read much more than he has.

I learned also that she had breast cancer, and while she was being treated wrote an incredibly moving treatise on illness — Illness as Metaphor — that redefined how we think about disease and the people who suffer from it. I learned that she wrote a sweeping novel on Immigration — In America — that won the U.S. National Book Award for Fiction.

I read her works, and it had a profound impact on me. I fell in love with her style, her wit, her intellectual strength, and her freshness of ideas. But our “marriage” was not to last. I accepted a professorship at University of Michigan, packed all my stuff up, including my picture of her, moved across the country to Ann Arbor, and never displayed her picture again. I recall when she died in December of 2004 that it felt like a void was left in me and in our country — that America had lost somebody that made me very proud to be an American — and wondering if it was possible again in the modern world to have another public intellectual of her stature and ability.

I was reminded of her again this past week upon reading the full transcript of her Rolling Stone Magazine interview by Jonathan Cott, recently released nearing the tenth anniversary of her death. It is a 168 page book published by Yale University Press, and it captures so well the sharpness of mind when she was at her peak in 1978. It brought me back immediately to those confusing times as a brand new assistant professor in Davis California, when it was unclear if the “life of the mind” was worth it, given so many other things to do in the world. Reading her words and feeling the power that comes from thinking and expressing and reasoning encouraged me. She was an inspiration to many, and ten years on after her death, her influence remains powerful.

I should not end without words directly her. From Cott’s Rolling Stone interview:
“I cannot understand the truth except as the negation of falsehood. I always discover what I think to be true by seeing that something else is false: the world is basically full of falsehood, and the truth is something carved out by the rejection of falsehood. In a way, the truth is quite empty, but it’s already a fantastic liberation to be free of falsehood.”

Categories: Variegations

Supersymmetry finds its way into literary fiction

January 10, 2014 Comments off

Louise Erdrich is one of America’s finest writers of literary fiction. I am partial to her because of her excellent writing and Native American themes that run through her work. I stumbled across a passage in her 2010 novel Shadow Tag that discusses supersymmetry — an elegant but speculative theory framework that relates boson particles to fermion particles. It’s the first discussion of supersymmetry I have seen in literary fiction, and it’s interesting how it is evoked. Here’s the passage:

“What kind of particle are you?

A worthy question, Top Quark. Let me think.

Florian smoked for a while, looking out over the constant motion of the lights.

Okay, I got it. I was going to say I am a tau, but no, I think I’m an unobserved particle. I’m only hypothetical. An electron gets a selectron. For every tau there is a stau. Floridan sang, For every muon there is a smuon.

A smuon?

They started laughing, tried to stop. Floridan started up again every time Riel said, Smuon?

For real. Smuon.

Florian got up and walked to the edge of the roof. For every muon there is a smuon! He sang and then pirouetted against the sky like a dancer in an old black-and-white movie.”

Categories: Variegations

Advice from the Soviet Union on how to become a great physicist

December 20, 2013 Comments off

Whatever you might think of the Soviet Union, they undeniably had incredible physicists. There are many reasons for this, but a culture of grit and personal determination to tackle physics problems on one’s own appears to me to be one of the key factors. To illustrate, here’s a quote from I.V. Savelyev, author of the three-volume “Physics. A General Course”, a successful Soviet-era textbook of undergraduate physics:

“The solving of problems will yield the maximum returns only if a student does this by himself. It is often not easy to solve a problem without any aid or prompting, and this is not always successful. But even unsuccessful attempts to find a solution, if they were undertaken with sufficient persistence, will give noticeable returns because they develop thinking and strengthen one’s will power. It must be borne in mind that the decisive role in working on problems, as in general in studying, is played by will power and diligence.” (italics are the author’s)

From first paragraph of I.V. Savelyev, “Questions and Problems in General Physics,” Mir Publishers, Moscow, 1982 (English 1984).

Categories: Education

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