1,720,968 research outputs found
Dark coupling (art no. 034, 2009)
No full textThe two dark sectors of the universe - dark matter and dark energy - may interact with each other. Background and linear density perturbation evolution equations are developed for a generic coupling. We then establish the general conditions necessary to obtain models free from early time non-adiabatic instabilities. As an application, we consider a viable universe in which the interaction strength is proportional to the dark energy density. The scenario does not exhibit "phantom crossing" and is free from instabilities, including early ones. A sizeable interaction strength is compatible with combined WMAP, HST, SN, LSS and H(z) data. Neutrino mass and/or cosmic curvature are allowed to be larger than in non-interacting models. Our analysis sheds light as well on unstable scenarios previously proposed
Phenomenology of symmetry breaking from extra dimensions
No full textMotivated by the electroweak hierarchy problem, we consider theories with two extra dimensions in which the four-dimensional scalar fields are components of gauge boson in full space. We explore the Nielsen-Olesen instability for SU(N) on a torus, in the presence of a magnetic background. A field theory approach is developed, computing explicitly the minimum of the complete effective potential, including tri-linear and quartic couplings and determining the symmetries of the stable vacua. We also develop appropriate gauge-fixing terms when both Kaluza-Klein and Landau levels are present and interacting, discussing the interplay between the possible six and four dimensional choices. The equivalence between coordinate dependent and constant Scherk-Schwarz boundary conditions — associated to either continuous or discrete Wilson lines — is analyzed
Dark coupling and gauge invariance
Full text linkWe study a coupled dark energy-dark matter model in which the energy-momentum exchange is proportional to the Hubble expansion rate. The inclusion of its perturbation is required by gauge invariance. We derive the linear perturbation equations for the gauge invariant energy density contrast and velocity of the coupled fluids, and we determine the initial conditions. The latter turn out to be adiabatic for dark energy, when assuming adiabatic initial conditions for all the standard fluids. We perform a full Monte Carlo Markov Chain likelihood analysis of the model, using WMAP 7-year data
Neutrino mixing and CP-violation
No full textThe prospects of measuring the leptonic angles and CP-odd phases at a neutrino factory are discussed in two scenarios: 1) three active neutrinos as indicated by the present ensemble of atmospheric plus solar data; 2) three active plus one sterile neutrino when the LSND signal is also taken into account. For the latter we develop one and two mass dominance approximations. The appearance of wrong sign muons in long baseline experiments and tau leptons in short baseline ones provides the best tests of CP-violation in scenarios 1) and 2), respectively.The prospects of measuring the leptonic angles and CP-odd phases at a neutrino factory are discussed in two scenarios: 1) three active neutrinos as indicated by the present ensemble of atmospheric plus solar data; 2) three active plus one sterile neutrino when the LSND signal is also taken into account. For the latter we develop one and two mass dominance approximations. The appearance of wrong sign muons in long baseline experiments and tau leptons in short baseline ones provides the best tests of CP-violation in scenarios 1) and 2), respectively.The prospects of measuring the leptonic angles and CP-odd phases at a neutrino factory are discussed in two scenarios: 1) three active neutrinos as indicated by the present ensemble of atmospheric plus solar data; 2) three active plus one sterile neutrino when the LSND signal is also taken into account. For the latter we develop one and two mass dominance approximations. The appearance of wrong sign muons in long baseline experiments and tau leptons in short baseline ones provides the best tests of CP-violation in scenarios 1) and 2), respectively.The prospects of measuring the leptonic angles and CP-odd phases at a neutrino factory are discussed in two scenarios: 1) three active neutrinos as indicated by the present ensemble of atmospheric plus solar data; 2) three active plus one sterile neutrino when the LSND signal is also taken into account. For the latter we develop one and two mass dominance approximations. The appearance of wrong sign muons in long baseline experiments and tau leptons in short baseline ones provides the best tests of CP-violation in scenarios 1) and 2), respectively.The prospects of measuring the leptonic angles and CP-odd phases at a neutrino factory are discussed in two scenarios: (1) three active neutrinos as indicated by the present ensemble of atmospheric plus solar data; (2) three active plus one sterile neutrino when the LSND signal is also taken into account. For the latter we develop one and two mass dominance approximations. The appearance of wrong sign muons in long baseline experiments and tau leptons in short baseline ones provides the best tests of CP-violation in scenarios (1) and (2), respectively
Fat Brane Phenomena
No full textGravitons could permeate extra space dimensions inaccessible to all other particles, which would be confined to ``branes''. We point out that these branes could be ``fat'' and have a non-vanishing width in the dimensions reserved for gravitons. In this case the other particles, confined within a finite width, should have ``branon'' excitations. Chiral fermions behave differently from bosons under dimensional reduction, and they may --or may not-- be more localized than bosons. All these possibilities are in principle testable and distinguishable, they could yield spectacular signatures at colliders, such as the production of the first branon excitation of 's or 's, decaying into their ground state plus a quasi-continuum of graviton recurrences. We explore these ideas in the realm of a future lepton collider and we individuate a {\it dimensiometer}: an observable that would cleanly diagnose the number of large ``extra'' dimensions.Gravitons could permeate extra space dimensions inaccessible to all other particles, which would be confined to ``branes''. We point out that these branes could be ``fat'' and have a non-vanishing width in the dimensions reserved for gravitons. In this case the other particles, confined within a finite width, should have ``branon'' excitations. Chiral fermions behave differently from bosons under dimensional reduction, and they may --or may not-- be more localized than bosons. All these possibilities are in principle testable and distinguishable, they could yield spectacular signatures at colliders, such as the production of the first branon excitation of 's or 's, decaying into their ground state plus a quasi-continuum of graviton recurrences. We explore these ideas in the realm of a future lepton collider and we individuate a {\it dimensiometer}: an observable that would cleanly diagnose the number of large ``extra'' dimensions.Gravitons could permeate extra space dimensions inaccessible to all other particles, which would be confined to “branes”. We point out that these branes could be “fat” and have a non-vanishing width in the dimensions reserved for gravitons. In this case the other particles, confined within a finite width, should have “branon” excitations. Chiral fermions behave differently from bosons under dimensional reduction, and they may – or may not – be more localized than bosons. All these possibilities are in principle testable and distinguishable, they could yield spectacular signatures at colliders, such as the production of the first branon excitation of γ 's or Z 's, decaying into their ground state plus a quasi-continuum of graviton recurrences. We explore these ideas in the realm of a future lepton collider and we individuate a dimensiometer : an observable that would cleanly diagnose the number of large “extra” dimensions
Golden measurements at a neutrino factory (vol 579, pg 17, 2000)
No full textThe precision and discovery potential of a neutrino factory based on muon storage rings is studied. For three-family neutrino oscillations, we analyse how to measure or severely constraint the angle , CP violation, MSW effects and the sign of the atmospheric mass difference . We present a simple analytical formula for the oscillation probabilities in matter, with all neutrino mass differences non-vanishing, which clarifies the subtleties involved in disentangling the unknown parameters. The appearance of ``wrong-sign muons'' at three reference baselines is considered: 732 km, 3500 km, and 7332 km. We exploit the dependence of the signal on the neutrino energy, and include as well realistic background estimations and detection efficiencies. The optimal baseline turns out to be km). Analyses combining the information from different baselines are also presented
The axion and the Goldstone Higgs
Full text linkWe consider the renormalizable SO(5)/SO(4) sigma-model, in which the Higgs particle has a pseudo-Nambu-Goldstone boson character, and explore what the minimal field extension required to implement the Peccei-Quinn symmetry is, within the partial compositeness scenario. It turns out that the minimal model does not require the enlargement of the exotic fermionic sector. The addition of a singlet scalar suffices. We explore the implementation of the symmetry and the phenomenological predictions for photonic signals in axion searches for all models discussed. Because of the constraints imposed by partial compositeness on the exotic fermion sector in order to obtain the Standard Model fermion masses, the expected range of allowed axion-photon couplings turns out to be generically narrowed with respect to that of standard invisible axion models, impacting the experimental quest
Four species neutrino oscillations at -Factory: sensitivity and CP-violation
No full textThe prospects of measuring the leptonic angles and CP-odd phases at a {\em neutrino factory} are discussed in the scenario of three active plus one sterile neutrino. We consider the \nu_\mu \raw \nu_e LSND signal. Its associated large mass difference leads to observable neutrino oscillations at short ( km) baseline experiments. Sensitivities to the leptonic angles down to can be easily achieved with a 1 Ton detector. Longer baseline experiments ( km) with a 1 Kton detector can provide very clean tests of CP-violation especially through tau lepton detection
Dark coupling
No full text30 pages, 10 figures, 3 tables.-- Pre-print archive.The two dark sectors of the universe—dark matter and dark energy—may interact with each other. Background and linear density perturbation evolution equations are developed for a generic coupling. We then establish the general conditions necessary to obtain models free from non-adiabatic instabilities. As an application, we consider a viable universe in which the interaction strength is proportional to the dark energy density. The scenario does not exhibit ``phantom crossing'' and is free from instabilities, including early ones. A sizeable interaction strength is compatible with combined WMAP, HST, SN, LSS and H(z) data. Neutrino mass and/or cosmic curvature are allowed to be larger than in non-interacting models. Our analysis sheds light as well on unstable scenarios previously proposed.The
work of M.B.G., D.H. and L.L-H. was partially supported by CICYT through the
project FPA2006-05423 and by CAM through the project HEPHACOS, P-ESP-00346.
Furthermore, the work of all authors is partially supported by the PAU (Physics of
the accelerating universe) Consolider Ingenio 2010. D.H. also acknowledges financial
support from the spanish government through a FPU fellowship AP20053603. The
work of L.L-H receives financial support through a postdoctoral fellowship of the PAU
Consolider Ingenio 2010 and partially through F.M.R.S. and I.I.S.N. The work of O.
M. is financially supported by the spanish Ramon y Cajal program. The work of S.R.
was partially supported an Excellence Grant of Fondazione Cariparo.Peer reviewe
On the scalar potential of minimal flavour violation
Full text linkAssuming the Minimal Flavour Violation hypothesis, we derive the general scalar potential for fields whose background values are the Yukawa couplings. We analyze the minimum of the potential and discuss the fine-tuning required to dynamically generate the mass hierarchies and the mixings between different quark generations. Two main cases are considered, corresponding to Yukawa interactions being effective operators of dimension five or six (or, equivalently, resulting from bi-fundamental and fundamental scalar fields, respectively). At the renormalizable and classical level, no mixing is naturally induced from dimension five Yukawa operators. On the contrary, from dimension six Yukawa operators one mixing angle and a strong mass hierarchy among the generations result
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