Quantum matters

Francesco Sannino and Jessica Turner

The LUX-ZEPLIN collaboration recently reported a candidate nuclear recoil with a reconstructed energy of about 248 keV. It appeared in an extended search window, in a region where the expected background is low. The reported global significance is 2.6 sigma: intriguing, but not enough to establish a dark-matter signal. Whether the event belongs to a background population or points to something new is still an open experimental question.
LZ report: https://arxiv.org/abs/2609.02823

For theorists, it raises another question: what kind of dark matter could produce such an energetic recoil while leaving relatively little activity at lower energies?

The event has already prompted more than 60 papers exploring possible explanations. While we wait for new experimental results, this work is showing which dark-matter models could account for such a recoil, and what other constraints they must satisfy. Those lessons will stay useful even if the event turns out to be background.

In our recent work, we explore a possibility rooted in strong dynamics. Like the protons and neutrons in ordinary matter, dark matter could be composite, with constituents bound by a new confining interaction. In our construction, a dark baryon has two nearly degenerate mass states. When it scatters off a nucleus, the lighter state converts into the heavier one. This “inelastic” scattering needs extra energy, which sets a threshold that suppresses low-energy recoils.

We consider an illustrative dark-baryon mass of one TeV and a mass difference of 300 keV. This benchmark falls within LZ’s published interval for this type of interaction. Its predicted rate depends sensitively on the fastest particles in the assumed Galactic dark-matter distribution. Establishing that the model is fully viable will also take more work on its cosmological abundance and dark-sector decays.
Our paper: https://arxiv.org/abs/2609.24988

Additional nuclear recoil data could test this explanation, alongside collider searches for the particle that mediates the interaction. The reach of those searches depends on the model’s couplings and decay channels.
Tests discussed in our paper: https://arxiv.org/html/2609.24988v1#S4

One event cannot establish what dark matter is. But the effort to explain it is helping us work out which inelastic dark matter models survive existing constraints and how to test them next. Even if this recoil turns out to be background, that work will help shape future searches.

The Standard Model stands as the cornerstone of our understanding of the fundamental constituents of the universe and their interactions. Developed over decades of ground breaking experimental observations and theoretical advancements, the Standard Model provides a comprehensive framework that elegantly describes the elementary particles and the forces governing their behavior. The model unifies the electromagnetic, weak, and strong nuclear forces.

Within the Standard Model, quarks and leptons constitute the building blocks of matter, while gauge bosons mediate the fundamental forces. The Higgs boson, discovered in 2012, endows particles with mass, completing the model’s intricate tapestry.

Despite its unparalleled success in explaining a myriad of experimental results, the Standard Model has its own enigmas. Unexplored realms, such as dark matter, and the hierarchical nature of particle masses, hint at physics beyond the Standard Model. As researchers delve into these mysteries, the Standard Model continues to serve as a guide, challenging minds to unravel the deeper intricacies of the universe’s most fundamental constituents.

However, the very same success of the Standard Model has increased the challenges and complexities involved in comparing theoretical predictions with experimental results. In fact, reducing theoretical uncertainty through higher order computations suggests a need for more accurate and refined theoretical predictions. To this scope, higher order computations are crucial for improving the precision of theoretical predictions and reducing uncertainties when comparing them with experimental data.

Additionally, exploring new sectors within the Standard Model, such as those involving composite operators featuring multiple Higgs particles, adds to the ongoing quest to understand the fundamental nature of particles and their interactions. This exploration could potentially lead to the discovery of new phenomena or particles that extend beyond the current understanding provided by the Standard Model.

To inch forward in this direction, in our recent work we have shown how to determine the quantum corrections for the family of lowest-lying Higgs operators with fixed hypercharge Q. We determined their anomalous dimensions to infinite orders in the Standard Model coupling strengths and leading and subleading orders in Q. 

In summary, the constant interplay between theoretical advancements and experimental investigations is essential for pushing the boundaries of our knowledge in particle physics and addressing the remaining questions and uncertainties within the field.

Unlocking the Mysteries of Dilatonic Dynamics: Impacts on Skyrme Structures In the realm of theoretical physics, there exists a fascinating area of …

Quantum Crystals, Branes and Spheres for Nuclear and Particle Physics: The Dilaton Story

Present and future gravitational-wave detectors are revolutionizing our approach to observing and exploring our universe. They offer a unique opportunity to explore new realms of physics in an entirely novel manner.

Observatories such as NANOGrav and the Laser Interferometer Space Antenna (LISA) are capable of detecting the background of gravitational waves generated by powerful cosmic events, including first-order phase transitions that occurred in the early universe. These events are highly sensitive to the presence of new particles and interactions that influence both the strength and the shape of the emitted gravitational wave spectrum.

Our primary question of interest is as follows:

Can novel composite dark sectors be detectable by present and future gravitational wave observatories ?

Alongside the international community we have been investigating for the past years different aspects of this important and technically challenging question. Capitalising on a number of methodologies, in our latest work https://inspirehep.net/literature/2704913 we presented under which conditions a first-order phase transition in relevant composite dark sectors can yield an observable stochastic gravitational-wave signal.

Over the past years, our work has complemented the one of the international scientific community in investigating various facets of this crucial and technically challenging question. Utilizing a range of methodologies, our latest research, available at https://inspirehep.net/literature/2704913, elucidates the conditions under which a first-order phase transition within relevant composite dark sectors can produce an observable stochastic gravitational-wave signal.

There are no celestial objects that draw more attention than black holes. The reason is that they are safe keepers of many deep classical and quantum physics secrets. And humans love to be in on a secret, especially when hidden in plain sight. In fact, we have images of black holes thanks to the Event Horizon Telescope and we have even heard the sound of two black holes colliding by converting in sound waves the gravitational waves registered by LIGO sent out during the collision.

These amazing experimental results confirm and celebrate Einstein’s theory of gravity. But what happens when the quantum physics kicks in?You may ask, why do we care? After all astrophysical black holes are far away from a quantum regime. True, but in the early universe mini quantum black holes are formed and even ordinary black holes can evaporate, thanks to Hawking radiation, to a quantum size. Last but not least the inside of a black hole surely carries quantum knowledge. One can invoke string theory or some other extension of classical gravity to gain information, but this will be partial and model dependent.

What can we do to unearth universal information about quantum gravity and specifically quantum black hole physics in absence of a fundamental theory of quantum gravity?

Using symmetries and well defined expansions including near the event horizon we developed in our work a model-independent approach. The latter allows us to compute important thermodynamical quantities of the black hole, such as the Hawking temperature and entropy, for which we provide model-independent expressions. Moreover, we show that imposing the absence of curvature singularities at the event horizon leads to non-trivial consistency conditions for the metric deformations themselves, which are violated by some earlier quantum black hole models.

Our framework offers exciting opportunities for quantum gravity phenomenology. Indeed, by being able to systematically extract physical quantities and compare them with observations, we can test and constrain concrete quantum gravity models, bridging the gap between theoretical ideas and experimental verifiability.

Understanding the quantum nature of space-time is an open challenge both from a theoretical and an experimental point of view. Quantum gravity effects are crucial, for example, in gravitational collapse of astrophysical objects, in understanding the inner working of black holes and Hawking thermodynamics as well as in the evaporation process of Planck-size black holes. Once the form of the quantum corrections for black hole physics is known, it can be studied via gravity wave observatories and black hole imaging techniques. Rather than speculating on the noble endeavour of an ultimate nature of quantum gravity, I believe that it is more impactful to construct effective frameworks allowing to parametrise quantum corrections to Einstein’s theory of general relativity to extract reliable predictions (see https://journals.aps.org/prd/pdf/10.1103/PhysRevD.106.046006).

In our recent work https://arxiv.org/pdf/2305.12965.pdf we analyse the impact of positivity conditions (sometime known also as energy conditions) on static spherically symmetric deformations of the Schwarzschild space-time. The metric is taken to satisfy, at least asymp-
totically, the Einstein equation in the presence of a non-trivial stress-energy tensor, on which we impose various physicality conditions. We systematically study and compare the impact of these conditions on the space-time deformations. It is extremely exciting that the universal nature of our findings applies to both classical and quantum metric deformations with and without event horizons. The conditions have immediate impact on known models of quantum black holes and the construction of future ones.

An unsolved puzzle in quantum field theory is the absence or unexplained suppression of the otherwise legitimate presence in the theory of quantum chromodynamics (the strong force) of maximal violation of time reversal. In other words the movie of strong dynamics should run differently going forward and backward in time. The associated operator responsible for such a time violation is known as topological term. Because a good quantum theory respects Einstein’s special relativity (and locality) one can either speak of time violation or that the combined operation of charge conjugation and parity reversal (the physics in the mirror) is broken by the topological term but that the product CPT is preserved. 

The fascinating fact is that any resolution of the puzzle either requires new physical particles such as the axion and its siblings or new mechanisms in which time reversal is broken spontaneously or other exotic possibilities that indicate the presence of new physics. Experiments are now testing these ideas as you read this short article. 

Dealing with strong dynamics we must also face the technical challenge that it is hard to determine its physical consequences with pen and paper, and even super computers. Additionally, the situation becomes much more complicated if we wish to understand what happens when we squeeze strong matter very hard. This happens routinely in astrophysical objects such as neutron stars.

In our newly published work we investigate the sister theory of QCD, i.e. two-colour QCD at nonzero matter density and as function of the size of the time reversal breaking operator as well as the number of quarks. We show that the vacuum acquires a rich structure when the underlying CP violating operator is added to the theory. We discover novel phases and analyse the order of their transitions characterizing the dynamics of the odd and even number of quark flavours. Our results will guide numerical simulations and novel tests of the model’s dynamics. The results are also expected to better inform phenomenological applications of the model ranging from composite Higgs physics to strongly interacting massive dark matter models featuring number changing interactions.

It is always exciting to publish a paper but this one is quite interesting to me, because provides a new link between safe theories and string theory, allowing for novel and relevant physical applications for string theory.

Safe theories are quantum field theories whose continuum limit is defined by a non-Gaussian ultraviolet fixed point when the ultraviolet cutoff is removed. They constitute an important set in the space of quantum field theories and were discovered in four dimensions here. The phase diagram in the interaction strength and their energy dependence is shown below.

In the newly published paper we develop the ‘safe’ gauge-string correspondence program according to which d-dimensional safe gauge theories are holographically dual to d+1 dimensional safe noncritical string theories on asymptotically anti-de Sitter space.

We provide evidences for this correspondence on a class of safe templates that engage fermion and scalar matter fields into gauge, Yukawa and Higgs self-interactions.

We further argue that four-dimensional super Yang-Mills theories and all known interacting (super)conformal field theories are nonperturbative limit situations of safe gauge theories.

Our result opens the door to many novel string theory applications for non supersymmetric theories.