phenomenology

Welcome, Prof. Jakob Moritz!

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String theorist Jakob Moritz joined the faculty as an assistant professor of physics on January 1, 2025. He joins us from CERN where he has been a postdoc for just over a year. Previously, he was a postdoc for four years at Cornell University, and before that, he earned his PhD from the University of Hamburg and DESY.

Please give a general overview of your research.

I work on string theory, a theoretical framework for quantum gravity. It is the only known approach that consistently combines quantum mechanics and Einstein’s theory of gravity. Physicists have struggled for decades to reconcile these two fundamental theories, and string theory achieves this unification. Sometimes called “the theory of everything,” string theory addresses physical phenomena at arbitrarily high energies. While the nickname may sound a bit grandiose, it highlights the theory’s incredible scope.

However, while the field equations of string theory have solutions that are relatively easy to study, these don’t resemble our universe. My research focuses on going beyond these “easy” solutions to find ones that better match the universe we observe. By doing so, I aim to uncover insights into the origins of the peculiar laws of physics governing our universe.

Something that I find particularly interesting is dimensionless constants of nature. These constants are significant because they are independent of a choice of units. For example, the ratio of the electron’s mass to the top quark’s mass is a dimensionless number — about 0.000003, which is remarkably small! There are many such constants whose values are determined experimentally, yet we lack a theoretical explanation for them.

In the early 20th century, particle physicists didn’t focus much on questions like, “Why are the constants of nature what they are, and not something else?” But with string theory, we can begin to address this. My work seeks to identify solutions of string theory in which these numbers align with experimental values. Another well-known example is the energy density of the vacuum, or dark energy. Despite being the dominant energy source in the universe today, dark energy is extraordinarily small in natural units — just 10^{-120} when compared to the natural energy scale of quantum gravity. This discrepancy, known as the cosmological constant problem, is something I find deeply intriguing. How can such a small value arise? Why isn’t it zero? Similarly, why is the Higgs mass so small? These are the kinds of profound questions I aim to explore through string theory.

What are one or two main projects you’ll have new group members work on?

One major project will involve finding the Standard Model of particle physics within string theory. This is something I am already working on, but having more hands on deck would be invaluable. The goal is to “engineer” realistic laws of particle physics — either the Standard Model or something close to it — as solutions of string theory. This work is crucial for addressing the electroweak hierarchy problem: why is the Higgs mass so unnaturally small? Currently, no one has a clear explanation for this.

Technically, this involves a lot of geometry. String theory predicts the existence of extra dimensions, which are both a blessing and a curse. They must be small enough to have remained unobservable, yet they also determine the physical laws we experience at larger scales. Much of our work will focus on understanding these geometries — particularly how certain objects, called branes, wrap around features like circles in these spaces — and calculating the resulting physical laws.

What attracted you to Madison and the university?

I really appreciate the breadth of the theory department here. String theory is a vast field, encompassing topics that range from almost pure mathematics to particle phenomenology. Because my work leans toward the phenomenological side, it intersects with many other areas of theoretical physics, including cosmology, particle physics, and applied mathematics. Being at a large place like Madison, with its diverse and talented faculty, is incredibly exciting.

Additionally, I know that Madison attracts outstanding students who are eager to work on string theory and particle physics. That’s something I’m looking forward to as well!

What is your favorite element and or elementary particle?

Neutrinos are cool because they’re almost massless. For a long time, they were thought to have zero mass, as predicted by the Standard Model of particle physics. But experiment has revealed otherwise! This discovery hints strongly at new physics at high energies.

What hobbies and interests do you have?

I love music! I play piano and guitar, and music is a big part of my life, especially since my partner is also a musician. I also enjoy sailing. While at Cornell, I spent summers sailing and participated in weekly competitive races, which were incredibly fun. I know that sailing is also a thing here — I look forward to getting back on the water!

Vernon Barger elected AAAS Fellow

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This story is modified from one published by University Communications 

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Vernon Barger

Eight University of Wisconsin­–Madison scholars — including physics professor Vernon Barger — have been elected fellows of the American Association for the Advancement of Science, the world’s largest general scientific society.

Barger was elected for “seminal work in studying fundamental particles at colliders and leadership in particle phenomenology, where theory meets experiment.”

This year, 502 scientists, engineers and innovators were chosen from the AAAS membership to be AAAS Fellows. The honor, presented annually since 1874, recognizes efforts to advance science and society, with the fellows chosen to reflect the highest standards of scientific integrity and professional ethics.

“As we celebrate the 150th anniversary of the AAAS Fellows, AAAS is proud to recognize the newly elected individuals,” said Sudip S. Parikh, AAAS chief executive officer and executive publisher of the Science family of journals. “This year’s class embodies scientific excellence, fosters trust in science throughout the communities they serve and leads the next generation of scientists while advancing scientific achievements.”

The new class of fellows will be featured in the April issue of the journal Science, and each new fellow will be celebrated at a September event in Washington, D.C.

Yang Bai promoted to full professor

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Yang Bai

The Department of Physics is pleased to announce that Prof. Yang Bai has been promoted to the rank of full professor.

“It is my pleasure and honor as Dean to approve Prof. Yang Bai’s promotion to Full Professor. His creativity and impressive breadth in particle physics research make him a leader not only on dark matter, but also more generally on Beyond-the-Standard-Model Physics,” says Eric Wilcots, Dean of the College of Letters & Science. “He is also a valued teacher, appreciated by students especially at the graduate level. Graduate students and junior researchers in Madison are in good hands.”

Bai joined the department in 2012, and was promoted to associate professor in 2017. In addition to his robust and well-funded research program, he has trained several successful graduate students, taught all levels of departmental courses, and served on several departmental and university committees.

“Professor Yang Bai is widely recognized as one of the leading theoretical particle physicists of his generation with a broad and vigorous research program, covering both the collider-related frontiers and the cosmic frontier. His work includes significant contributions in essentially every area related to dark matter,” says Sridhara Dasu, professor and department chair. “The Physics Department very strongly endorses the promotion of Yang Bai to Full Professor.”

Congrats, Prof. Bai on this well-earned recognition!

 

Vernon Barger earns 2021 APS Sakurai Prize

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Vernon Barger

University of Wisconsin­–Madison Physics professor Vernon Barger has won the J.J. Sakurai Prize for Theoretical Particle Physics, the American Physical Society announced October 7.

The J.J. Sakurai Prize is considered ­­one of the most prestigious annual prizes in the field of theoretical high energy physics. Barger, who joined the UW­–Madison faculty in 1965, is a world leader in theoretical particle physics where theory meets experiment. He is one of the founders of collider phenomenology as it is practiced today.

“This prize belongs to the hundreds of students, postdocs, faculty and visiting colleagues who entered the portal of UW–Madison to discover the quarks, leptons and bosons of particle physics,” Barger says. “Only at UW–Madison could this research at the interface of theory and experiment so thrive.”

The techniques that Barger helped develop have been crucial in establishing the experimental foundations of the Standard Model of particle physics and in guiding the search for signals of new physics. His contributions have played a key role in many important milestones in particle physics, including the discovery of the W boson in 1985, the top quark in 1995, and the Higgs boson discovery in 2012.

UW–Madison physics professor Lisa Everett and University of Hawaii professor Xerxes Tata, both phenomenologists, co-nominated Barger for the prize.

“We are thrilled that Vernon Barger has been awarded the 2021 J.J. Sakurai Prize, for which we nominated him for his seminal accomplishments and leadership record in collider physics phenomenology over five decades in the field,” Everett says. “The techniques he has pioneered have and continue to be of pivotal importance for elucidating physics signals at particle colliders, and these contributions are only part of a very long and distinguished research career in theoretical particle physics. He is highly deserving of this honor.”

UW–Madison chemistry professor Martin Zanni also won an APS award, the Earle K. Plyler Prize for Molecular Spectroscopy & Dynamics. Read the UW–Madison news piece about both Barger and Zanni’s awards here.