Artículos con la etiqueta ‘High Energy Physics – Phenomenology (hep-ph)’

Fermi and the Theory of Weak Interactions

Por • 15 mar, 2014 • Category: Educacion

The history of weak interactions starting with Fermi’s creation of the beta decay theory and culminating in its modern avatar in the form of the electroweak gauge theory is described. Discoveries of parity violation, matter-antimatter asymmetry, W and Z bosons and neutrino mass are highlighted.



Ya. B. Zeldovich (1914-1987): Chemist, Nuclear Physicist, Cosmologist

Por • 8 mar, 2014 • Category: Ambiente

Ya.B. Zeldovich was a pre-eminent Soviet physicist whose seminal contributions spanned many fields ranging from physical chemistry to nuclear and particle physics, and finally astrophysics and cosmology. March 8, 2014 marks Zeldovich’s birth centenary, and this article attempts to convey the zest with which Zeldovich did science, and the important role he played in fostering and mentoring a whole generation of talented Scientists.



A Critical History of Renormalization

Por • 22 oct, 2013 • Category: Crítica

The history of renormalization is reviewed with a critical eye, starting with Lorentz’s theory of radiation damping, through perturbative QED with Dyson, Gell-Mann & Low, and others, to Wilson’s formulation and Polchinski’s functional equation, and applications to “triviality”, and dark energy in cosmology.



The genesis of the quantum theory of the chemical bond

Por • 22 sep, 2013 • Category: Leyes

n historical overview is given of the relevant steps that allowed the genesis of the quantum theory of the chemical bond, starting from the appearance of the new quantum mechanics and following later developments till approximately 1931. General ideas and some important details are discussed concerning molecular spectroscopy, as well as quantum computations for simple molecular systems performed within perturbative and variational approaches, for which the Born-Oppenheimer method provided a quantitative theory accounting for rotational, vibrational and electronic states. The novel concepts introduced by the Heitler-London theory, complemented by those underlying the method of the molecular orbitals, are critically analyzed along with some of their relevant applications.



The High-Energy Interpretation of Quantum Mechanics

Por • 13 sep, 2013 • Category: Crítica

We address the issue of the interpretation of quantum mechanics by asking why the issue never arises in the description of high-energy interactions. We argue that several tenets of quantum mechanics, specifically the collapse of the wave function, follow directly once one accepts the essential randomness of fundamental interaction events. We then show that scale separation of fundamental interactions ensures that decoherent measurement can be unambiguously separated from the random quantum events. Finally, we argue that the fundamental symmetries of space and time guarantee the existence of a unique preferred basis. We argue that this set of ideas might lead to an interpretation of quantum mechanics, or rather, show in which sense an “interpretation” is (or is not) necessary.



QED Second Order Corrections on the Speed of Light at Low Temperature

Por • 24 ago, 2013 • Category: Crítica

We want to study thermal corrections on the speed of light at low temperature considering temperature dependence of photon vacuum polarization tensor at two-loop level in the standard QED. It is found that the heat bath behaves as a dispersive medium to the propagation of light and reduces its speed proprtional to the second order of temperature. Similiraties and differences with already known calculations which are based on Euler-Heisenberg Lagrangian and/or those using temperature dependent electromagnetic properties of the medium are discussed.



Multiversality

Por • 30 jul, 2013 • Category: Leyes

Valid ideas that physical reality is vastly larger than human perception of it, and that the perceived part may not be representative of the whole, exist on many levels and have a long history. After a brief general inventory of those ideas and their implications, I consider the cosmological “multiverse” much discussed in recent scientific literature. I review its theoretical and (broadly) empirical motivations, and its disruptive implications for the traditional program of fundamental physics. I discuss the inflationary axion cosmology, which provides an example where firmly rooted, plausible ideas from microphysics lead to a well-characterized “mini-multiverse” scenario, with testable phenomenological consequences.



Is the CMB telling us that dark matter is weaker than weakly interacting?

Por • 9 jul, 2013 • Category: Leyes

If moduli, or other long-lived heavy states, decay in the early universe in part into light and feebly interacting particles (such as axions), these decay products could account for the additional energy density in radiation that is suggested by recent measurements of the CMB. These moduli decays will also, however, alter the expansion history of the early universe, potentially diluting the thermal relic abundance of dark matter. If this is the case, then dark matter particles must annihilate with an even lower cross section than required in the standard thermal scenario (sigma v < 3×10^-26 cm^3/s) if they are to make up the observed density of dark matter. This possibility has significant implications for direct and indirect searches for dark matter.



The most powerful particles in the Universe: a cosmic smash

Por • 9 may, 2013 • Category: Crítica

This year we are celebrating 101 years since the discovery of cosmic rays. They are whizzing all around the Universe, and they occur at very different energies, including the highest particle energies that exist. However, theory predicts an abrupt suppression (a “cutoff”) above a specific huge energy. This is difficult to verify, the measurements are controversial, but it provides a unique opportunity to probe established concepts of physics – like Lorentz Invariance – under extreme conditions. If the observations will ultimately contradict this “cutoff”, this could require a fundamental pillar of physics to be revised.



From old to new particles: a simple symmetry is guiding us

Por • 5 ene, 2013 • Category: Leyes

There exists one experimental result that cannot be explained by the Standard Model (SM), the current theoretical framework for particle physics: non-zero masses for the neutrinos (elementary particles travelling close to light speed, electrically neutral and weakly interacting). The SM erroneously assumes that they are massless. Therefore, particle physicists are now exploring new physics beyond the SM. There is strong anticipation that we are about to unravel it, in the form of new matter and/or forces, at the Large Hadron Collider (LHC), presently running at CERN. We discuss a minimal extension of the SM, based on a somewhat larger version of its symmetry structure and particle content, that can naturally explain the existence of neutrino masses while also predicting novel signals accessible at the LHC, including a light Higgs boson, as evidenced by current data.