Journal Club

Seminar Room

Monday 9th of May, 2016

Hour: 10:00

Title: A Simple U(1) Gauge Theory Explanation of the Diphoton Excess

Presented by: Roberto Vega-Morales

Ref: http://arxiv.org/abs/1512.06426v2

Abstract:

The recent ATLAS and CMS diphoton resonance excesses are explored in a simple U(1) gauge theory extension of the Standard Model where the resonance is the Higgs boson of the U(1) symmetry breaking, ϕ. This particle couples to exotic quarks which, through loops, can produce a large enough rate to explain the excess. Due to the choice of U(1) charges, flavor constraints are naturally suppressed, allowing arbitrary flavor violation in the decays of the new quarks to up-type quarks, modifying their signal topologies. An additional heavy quark in the model decays to the lighter exotic quark by emitting either ϕ or the U(1) gauge boson, Ax, giving extra signals containing diphoton and digluon resonances. Finally, the new Higgs can decay into γAx and ZAx, followed by Ax decaying into Standard Model fermions through kinetic mixing. Thus, this model gives interesting modified signals to the general class of exotic quark models explaining the diphoton resonance.

Hour: 10:00

Title: Hunting for Dark Particles with Gravitational Waves

Presented by: Roberto Vega-Morales

Ref: https://arxiv.org/abs/1605.01209v1

Abstract:

The LIGO observation of gravitational waves from a binary black hole merger has begun a new era in fundamental physics. If new dark sector particles, be they bosons or fermions, can coalesce into exotic compact objects (ECOs) of astronomical size, then the first evidence for such objects, and their underlying microphysical description, may arise in gravitational wave observations. In this work we study how the macroscopic properties of ECOs are related to their microscopic properties, such as dark particle mass and couplings. We then demonstrate the smoking gun exotic signatures that would provide observational evidence for ECOs, and hence new particles, in terrestrial gravitational wave observatories. Finally, we discuss how gravitational waves can test a core concept in general relativity: Hawking's area theorem.

Hour: 10:00

Title: Laser Interferometers as Dark Matter Detectors

Presented by: Mar Bastero Gil

Ref: https://arxiv.org/abs/1605.01103v1

Abstract:

While global cosmological and local galactic abundance of dark matter is well established, its identity, physical size and composition remain a mystery. In this paper, we analyze an important question of dark matter detectability through its gravitational interaction, using current and next generation gravitational-wave observatories to look for macroscopic (kilogram-scale or larger) objects. Keeping the size of the dark matter objects to be smaller than the physical dimensions of the detectors, and keeping their mass as free parameters, we derive the expected event rates. For favorable choice of mass, we find that dark matter interactions could be detected in space-based detectors such as LISA at a rate of one per ten years. We then assume the existence of an additional Yukawa force between dark matter and regular matter. By choosing the range of the force to be comparable to the size of the detectors, we derive the levels of sensitivity to such a new force, which exceeds the sensitivity of other probes in a wide range of parameters. For sufficiently large Yukawa coupling strength, the rate of dark matter events can then exceed 10 per year for both ground- and space-based detectors. Thus, gravitational-wave observatories can make an important contribution to a global effort of searching for non-gravitational interactions of dark matter.

Hour: 10:00

Title: New Forces and the 750 GeV Resonance

Presented by: Roberto Vega-Morales

Ref: http://arxiv.org/abs/1604.05319v1

Abstract:

Recently, the ATLAS and CMS collaborations have pointed out the possible existence of a new resonance with a mass around 750 GeV. We investigate the possibility to identify this new resonance with a spin zero field responsible for the breaking of a new gauge symmetry. We focus on a simple theory where the baryon number is a local symmetry spontaneously broken at the low scale. In this context new vector-like quarks are needed to cancel all baryonic anomalies and define the production mechanism and decays of the new Higgs at the LHC. Assuming the existence of the new Higgs with a mass of 750 GeV at the LHC we find an upper bound on the symmetry breaking scale. Therefore, one expects that a new force associated with baryon number could be discovered at the LHC.

Hour: 10:00

Title: On the Charm Contribution to the Atmospheric Neutrino Flux

Presented by: Manuel Masip Mellado

Ref: https://arxiv.org/abs/1605.01409v1

Abstract:

We revisit the estimate of the charm particle contribution to the atmospheric neutrino flux that is expected to dominate at high energies because long-lived high-energy pions and kaons interact in the atmosphere before decaying into neutrinos. We focus on the production of forward charm particles which carry a large fraction of the momentum of the incident proton. In the case of strange particles, such a component is familiar from the abundant production of K+Λ pairs. These forward charm particles can dominate the high-energy atmospheric neutrino flux in underground experiments. Modern collider experiments have no coverage in the very large rapidity region where charm forward pair production dominates. Using archival accelerator data as well as IceCube measurements of atmospheric electron and muon neutrino fluxes, we obtain an upper limit on forward D¯0Λc pair production and on the associated flux of high-energy atmospheric neutrinos. We conclude that the prompt flux may dominate the much-studied central component and represent a significant contribution to the TeV atmospheric neutrino flux. Importantly, it cannot accommodate the PeV flux of high-energy cosmic neutrinos, nor the excess of events observed by IceCube in the 30--200 TeV energy range indicating either structure in the flux of cosmic accelerators, or a presence of more than one component in the cosmic flux observed.