particle-physics

When deriving LSZ reduction theorem Weinberg in his QFT book have assumed n-point generalized Green functions, $$ G(q_{1},...,q_{n}) = \int d^{4}x_{1}...d^{4}x_{n}e^{-i\prod_{i =1}^{n}q_{j}x_{j}} \langle |\hat {T}\left( \hat {O}_{l}(x_{1})\hat {A}_{2}(x_{2})...\hat A_{n}(x_{n})\right) |\rangle , \quad (1) $$ where $\hat {O}_{l}(x)$ transforms under the irreducible representation of the Lorentz gr…

Why is it that, in general, the particles produced/emitted during a given particle collision tend to be produced/emitted at angles relative to the beam axis? I can kind of see why this is true for collisions between composite particles, since then, using a classical analogy, as they collide the constituent particles will not necessarily experience a "head-on" collision - if they are not inline wi…

This is problem 2.7 from Griffiths' Introduction to Elementary Particles. Here are the two reactions that I am trying to examine: (c) ##\Sigma^0\rightarrow\Lambda+\pi^0## (g) ##\Delta^+\rightarrow p+\pi^0## According to Griffiths' solutions, (g) is possible, (c) is not possible due to... Read more

Scientific Reports, Published online: 22 August 2026; doi:10.1038/s41598-026-67596-6 Comparative fits to identified-hadron spectra in relativistic p+p, p+Pb, Pb+Pb and Au+Au collisions including error covariances

This paper opens up a lot of new possibilities to look for dark matter.

What happened in the first moments of the universe—before the building blocks of life and the world we know today came into existence? Physicists at the CERN research facility in Switzerland are trying to answer this question by recreating some of the extreme conditions that prevailed in the universe during its earliest history. Now, researchers […]

Under the Bohmian Interpretation (BM or BMI): Suppose we have a traditional pair of polarization entangled photons A and B going to Alice and Bob, who will test their polarizations in the same reference frame. To be specific, let's say A and B are entangled |HH> + |VV>. In the traditional... Read more

In Leptogenesis, CP-asymetry arises due to the interference of the tree-level amplitude $N\rightarrow l_\alpha\phi$ (where $N$ is heavy sterile neutrino, $l_\alpha$ is a lepton flavour, and $\phi$ is the Higgs) with the higher order amplitudes (say, one-loop amplitude). This was a decay. Let us consider an scattering so that there may me more than one diagrams at the tree level. For a given scatt…

This entry is about the notion of naturalness in (particle-)physics. For the notion in mathematics see at natural transformation. In (particle-)physics the term “naturalness” [‘t Hooft 1980, Gell- Mann 1983] refers to the vague idea that a model of physics is expected to work without requiring unlikely-looking ad-hoc coincidences or “fine-tuning” of its parameters (such as the choice of renormali…

For decades, scientists have puzzled over why certain atomic nuclei unexpectedly produce large numbers of low-energy gamma rays. A new experiment traced the effect to magnetic changes inside the nucleus, where protons and neutrons effectively flip their tiny internal magnets. The discovery could sharpen models of everything from nuclear reactions on Earth to the creation of heavy elements in star…

Unlike previous attempts to pinpoint viable physical theories using two-particle entanglement, genuine three-way connections now offer a distinct selection principle. Analysis reveals suppression of this tripartite entanglement specifically identifies both gauge-invariant and diffeomorphism-invariant models during particle collisions. This offers a new information-theoretic criterion for understa…

Constructions of particle collisions in standard laboratory coordinates demand more computational steps than alternative formulations utilising spin projection along motion. This disparity emerges when simulating high energy events like Bhabha scattering with quantum computers, revealing differing ‘magic’ requirements dependent on chosen reference frames. The study provides explicit circuits demo…

Given that the origin of the Alday-Gaiotto-Tachikawa (AGT) duality can be traced back to the compactification of the flat space $6$ d $(2,0)$ superconformal field theory J. Yagi, (2012) , I am curious about the possibility of extending this duality to nontrivial geometries. Meaning, if the compactification of $6$ d $(2,0)$ SCFT coupled to gravity A. P. Braun, M. Larfors, P.-K. Oehlmann, (2021) (s…

The parity transformation property of a complex scalar field $\phi(x)$ is given by: $$P\phi(t,\textbf{x}) P^{-1}=\eta_P\phi(t,-\textbf{x})$$ where $\eta_P=\pm 1$ . The charge conjugation property of a complex scalar field $\phi(x)$ is given by: $$C\phi(t,\textbf{x}) C^{-1}=\eta_C\phi^\dagger(t,\textbf{x})$$ where $\eta_C=\pm 1$ . Therefore, the CP transformation property of $\phi(x)$ can be worke…

This is problem 2.3 in Griffiths' Introducion to Elementary Particles. I have Griffiths' solutions, otherwise I would be completely lost. Nonetheless, I tried to come up with a solution of my own first. I found only one possibility, which looked ok to me, but it is not even among the 17 ones... Read more

Electrons are indivisible, yet in a strong magnetic field they can move as if they carried only a fraction of their charge. Mitali Banerjee’s group at EPFL has built a bilayer-graphene antidot—a small electrically defined energy hill—that measures those fractions directly. Quasiparticles circle the hill and tunnel at regular intervals as the magnetic field or gate voltage is swept. The spacing of…

The LHC has already fallen silent for Long Shutdown 3 (LS3), but elsewhere across CERN’s accelerator complex the pace remains intense. With just a week and a half of beam operation remaining, the countdown has begun for all the machines, which will switch off their beams at 6.00 a.m. on Monday, 31 August, marking the […]

On 31 July, colleagues and friends of theoretical physicist John Ellis came together to celebrate his 80th birthday and almost 60 years of service to CERN and the wider particle physics community. “Many of us were amazed to learn of John’s significant impact on fields besides our own,” said physicist Matthew McCullough, Deputy Head of […]

Regular matter makes up just one-sixth of all the matter in the universe. What would it mean to finally understand what makes up the rest?

Physicists know a lot about the most fundamental properties of the universe, but they certainly don’t know everything. 2021 was a big year for physics – what was learned and what’s coming next?