New quantum gravity theory: Are physicists getting closer to a unified theory of fundamental forces?

Amazing stuff, but way above my head! A new theory from Finland!

"At long last, a unified theory combining gravity with the other fundamental forces—electromagnetism and the strong and weak nuclear forces—is within reach. Bringing gravity into the fold has been the goal of generations of physicists, who have struggled to reconcile the incompatibility of two cornerstones of modern physics: quantum field theory and Einstein’s theory of gravity. ...

The key was finding a way to describe gravity in a suitable gauge theory — a kind of theory in which particles interact with each other through a field. ‘The most familiar gauge field is the electromagnetic field. ..."

From the abstract:

"The Standard Model of particle physics describes electromagnetic, weak, and strong interactions, which are three of the four known fundamental forces of nature.

The unification of the fourth interaction, gravity, with the Standard Model has been challenging due to incompatibilities of the underlying theories—general relativity and quantum field theory.

While quantum field theory utilizes compact, finite-dimensional symmetries associated with the internal degrees of freedom of quantum fields, general relativity is based on noncompact, infinite-dimensional external space-time symmetries.

The present work aims at deriving the gauge theory of gravity using compact, finite-dimensional symmetries in a way that resembles the formulation of the fundamental interactions of the Standard Model.

For our eight-spinor representation of the Lagrangian, we define a quantity, called the space-time dimension field, which enables extracting four-dimensional space-time quantities from the eight-dimensional spinors.

Four U(1) symmetries of the components of the space-time dimension field are used to derive a gauge theory, called unified gravity. The stress-energy-momentum tensor source term of gravity follows directly from these symmetries. The metric tensor enters in unified gravity through geometric conditions. We show how the teleparallel equivalent of general relativity in the Weitzenböck gauge is obtained from unified gravity by a gravity-gauge-field-dependent geometric condition. Unified gravity also enables a gravity-gauge-field-independent geometric condition that leads to an exact description of gravity in the Minkowski metric. This differs from the use of metric in general relativity, where the metric depends on the gravitational field by definition. Based on the Minkowski metric, unified gravity allows us to describe gravity within a single coherent mathematical framework together with the quantum fields of all fundamental interactions of the Standard Model.

We present the Feynman rules for unified gravity and study the renormalizability and radiative corrections of the theory at one-loop order.

The equivalence principle is formulated by requiring that the renormalized values of the inertial and gravitational masses are equal.

In contrast to previous gauge theories of gravity, all infinities that are encountered in the calculations of loop diagrams can be absorbed by the redefinition of the small number of parameters of the theory in the same way as in the gauge theories of the Standard Model. This result and our observation that unified gravity fulfills the Becchi–Rouet–Stora–Tyutin (BRST) symmetry and its coupling constant is dimensionless suggest that unified gravity can provide the basis for a complete, renormalizable theory of quantum gravity."

New quantum gravity theory: Are physicists getting closer to a “theory of everything”?

New theory of gravity brings long-sought Theory of Everything a crucial step closer (original news release) "A quantum theory of gravity would clear the path to answering some of the biggest questions in physics."

Gravity generated by four one-dimensional unitary gauge symmetries and the Standard Model (open access)

Mikko Partanen (left) and Jukka Tulkki, the two authors of this study

The neutrino remains too light/small to be weighed by the biggest machine ever created, 149 physicists, and 259 days of measurement

What a dilemma! What Herculean efforts to uncover the secrets of the universe! I am in awe! So we need even bigger machines or a novel approach!

"Using a 200-ton, blimplike metal chamber that looks like something out of Fritz Lang’s classic sci-fi movie Metropolis, 149 physicists have tried to measure the mass of the neutrino, the lightest and most elusive of matter particles—and have found that it’s too small to be weighed.

The Karlsruhe Tritium Neutrino Experiment (KATRIN) in Germany aims to weigh the nearly massless neutrino by observing the beta decay of tritium, a nucleus containing one proton and two neutrons. In the decay, one neutron turns into a proton, spitting out an electron and a neutrino and turning the nucleus into helium-3. By observing billions of decays and measuring the maximum energy of the electrons, researchers can infer the mass of the neutrino.

KATRIN finds that the neutrino must be lighter than 0.45 electronvolts (eV), lowering its previous limit by a factor of 2 “We now know very directly that the neutrino is at least a million times lighter than the next lightest fundamental particle, which is an electron,”  ..."

From the editor's summary and abstract:

"Editor’s summary

The neutrino, a weakly interacting, uncharged elementary particle, has been shown to have a nonzero mass, the exact value of which remains unknown. This is not what the usually very reliable Standard Model of particle physics predicts, which means that measuring the neutrino mass may offer hints of physics that this model cannot account for.

The KATRIN Collaboration used the beta-decay of molecular tritium to directly measure the mass of the antiparticle of a particular flavor of the neutrino  ...

Abstract

That neutrinos carry a nonvanishing rest mass is evidence of physics beyond the Standard Model of elementary particles. Their absolute mass holds relevance in fields from particle physics to cosmology.

We report on the search for the effective electron antineutrino mass with the KATRIN experiment. KATRIN performs precision spectroscopy of the tritium β-decay close to the kinematic endpoint. On the basis of the first five measurement campaigns, we derived a best-fit value of 

 eV2, resulting in an upper limit of mν < 0.45 eV at 90% confidence level. Stemming from 36 million electrons collected in 259 measurement days, a substantial reduction of the background level, and improved systematic uncertainties, this result tightens KATRIN’s previous bound by a factor of almost two."

ScienceAdviser

New KATRIN results (original news release) "Neutrinos weigh less than 0.45 electronvolts/c2 – precision scale KATRIN sets new record "

Direct neutrino-mass measurement based on 259 days of KATRIN data (no public access)

Direct neutrino-mass measurement based on 259 days of KATRIN data (preprint, open access)

Supercolliders: Four Ways Engineers Aim to Break Physics

Very recommendable! Notice how China is catching up in this area too!

"In particle physics, the smallest problems often require the biggest solutions [and gigantic machines]."

Supercolliders: Four Ways Engineers Aim to Break Physics - IEEE Spectrum "A quarkless supercollider may finally shed light on dark matter"

The Standard Model of particle physics is the current best theory of all the understood matter and forces in our universe (except gravity). The model works extremely well, but scientists also know that it is incomplete. The next generation of supercolliders might give a glimpse at what’s beyond the Standard Model.

FCC-ee would be a 91-km ring spanning underneath Switzerland and France, near the current Large Hadron Collider.

One of the proposed locations for the CEPC is near the northern port city of Qinhuangdao, where the 100 km circumference collider would be buried underground.

A new piece in the matter-antimatter symmetry puzzle

Amazing stuff!

"Yesterday, at the annual Rencontres de Moriond conference taking place in La Thuile, Italy, the LHCb collaboration at CERN reported a new milestone in our understanding of the subtle yet profound differences between matter and antimatter. In its analysis of large quantities of data produced by the Large Hadron Collider, the international team found overwhelming evidence that particles known as baryons, such as the protons and neutrons that make up atomic nuclei, are subject to a mirror-like asymmetry in nature’s fundamental laws that causes matter and antimatter to behave differently. The discovery provides new ways to address why the elementary particles that make up matter fall into the neat patterns described by the Standard Model of particle physics, and to explore why matter apparently prevailed over antimatter after the Big Bang. ...."

From the abstract:

"The Standard Model of particle physics, the theory of particles and interactions at the smallest scale, predicts that matter and antimatter interact differently due to violation of the combined symmetry of charge conjugation (C) and parity (P). Charge conjugation transforms particles into their antimatter particles, while the parity transformation inverts spatial coordinates. This prediction applies to both mesons, which consist of a quark and an antiquark, and baryons, which are composed of three quarks.

However, despite having been discovered in various meson decays, CP violation has yet to be observed in baryons, the type of matter that makes up the observable Universe.

This article reports a study of the decay of the beauty baryon Λ0b to the pK−π+π− final state and its CP-conjugated process, using data collected by the LHCb (Large Hadron Collider beauty) experiment at CERN.

The results reveal significant asymmetries between the decay rates of the Λ0b baryon and its CP-conjugated antibaryon, marking the first observation of CP violation in baryon decays, thus demonstrating the different behaviour of baryons and antibaryons.

In the Standard Model, CP violation arises from the Cabibbo-Kobayashi-Maskawa mechanism, while new forces or particles beyond the Standard Model could provide additional contributions. This discovery opens a new path to search for physics beyond the Standard Model."

A new piece in the matter-antimatter puzzle | symmetry magazine

Observation of charge-parity symmetry breaking in baryon decays (open access)

The Standard Model: The Most Successful Scientific Theory Ever

Very recommendable! Excellent presentation!

Intriguing new result from the LHCb experiment at CERN

Recommendable! About the not so settled science of the Standard Model! The particle zoo evolves ... Can you feel the excitement?

"Today [3/23/2021] the LHCb experiment at CERN announced new results which, if confirmed, would suggest hints of a violation of the Standard Model of particle physics. The results focus on the potential violation of lepton flavour universality ...
The new result indicates hints of a deviation from one: the statistical significance of the result is 3.1 standard deviations, which implies a probability of around 0.1% that the data is compatible with the Standard Model predictions. “If a violation of lepton flavour universality were to be confirmed, it would require a new physical process, such as the existence of new fundamental particles or interactions,” says LHCb spokesperson Professor Chris Parkes from the University of Manchester and CERN."

"... This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton-proton collision data collected with the LHCb detector at CERN's Large Hadron Collider. ... If confirmed by future measurements, this violation of lepton universality would imply physics beyond the Standard Model, such as a new fundamental interaction between quarks and leptons. ..."

Intriguing new result from the LHCb experiment at CERN | CERN The LHCb results strengthen hints of a violation of lepton flavour universality

Here is the link to the referenced research paper:

Test of lepton universality in beauty-quark decays

Six fabulous facts about the Standard Model

The U.S. Department of Energy is selling some rosy colored science glorification to the general public! The Standard Model may have served well, but it probably is insufficient or even wrong!

"... scientists build mathematical models that predict everything from the economy to the weather. ..." 

What a nonsense!

"Today in Symmetry, learn six fabulous facts about one of the most robust scientific models in the world. ..."

What a nonsense! "“A big open question is gravity,” Bose says. “We don’t have any way to account for gravity on subatomic scales.”"

Six fabulous facts about the Standard Model | symmetry magazine