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O. Panella

Publications and source records attributed to O. Panella.

At least 37 records · Page 2Linked to original sources
arXiv2012

Phenomenology of excited doubly charged heavy leptons at LHC

We consider the production at the LHC of exotic composite leptons of charge Q=+2e. Such states are allowed in composite models which contain extended isospin multiplets (Iw=1 and Iw=3/2). These doubly charged leptons couple with Standard Model [SM] fermions via gauge interactions, thereby delineating and restricting their possible decay channels. We discuss the production cross section at the LHC of L++ (p p --> L++, l-) and concentrate on the leptonic signature deriving from the cascade decays L++ --> W+, l+ --> l+, l+, ν_l i.e. p p --> l-, l+, l+, ν_l showing that the invariant mass distribution of the like-sign dilepton has a sharp end point corresponding to excited lepton mass m*. We find that the sqrt{s}=7 TeV run is sensitive at the 3-sigma (5-sigma) level to a mass of the order of 600 GeV if L=10 fb^-1 (L=20 fb^-1). The sqrt{s}=14 TeV run can reach a sensitivity at 3-sigma (5-sigma) level up to m*=1 TeV for L=20 fb^-1 (L=60 fb^-1).

hep-ph↗
arXiv2011

The Casimir Effect in Minimal Length Theories based on a Generalized Uncertainity Principle

We study the corrections to the Casimir effect in the classical geometry of two parallel metallic plates, separated by a distance $a$, due to the presence of a minimal length ($\hbar\sqrt{(β)}$) arising from quantum mechanical models based on a Generalized Uncertainty Principle (GUP). The approach for the quantization of the electromagnetic field is based on projecting onto the maximally localized states of a few specific GUP models and was previously developed to study the Casimir-Polder effect. For each model we compute the lowest order correction in the minimal length to the Casimir energy and find that it scales with the fifth power of the distance between the plates $a^{-5}$ as opposed to the well known QED result which scales as $a^{-3}$ and, contrary to previous claims, we find that it is always attractive. The various GUP models can be in principle differentiated by the strength of the correction to the Casimir energy as every model is characterized by a specific multiplicative numerical constant.

hep-th↗
arXiv2010

New exact solution of the one dimensional Dirac Equation for the Woods-Saxon potential within the effective mass case

We study the one-dimensional Dirac equation in the framework of a position dependent mass under the action of a Woods-Saxon external potential. We find that constraining appropriately the mass function it is possible to obtain a solution of the problem in terms of the hypergeometric function. The mass function for which this turns out to be possible is continuous. In particular we study the scattering problem and derive exact expressions for the reflection and transmission coefficients which are compared to those of the constant mass case. For the very same mass function the bound state problem is also solved, providing a transcendental equation for the energy eigenvalues which is solved numerically.

math-ph↗
arXiv2010

Electric Dipole Moments and Polarizability in the Quark-Diquark Model of the Neutron

For a bound state internal wave function respecting parity symmetry, it can be rigorously argued that the mean electric dipole moment must be strictly zero. Thus, both the neutron, viewed as a bound state of three quarks, and the water molecule, viewed as a bound state of ten electrons two protons and an oxygen nucleus, both have zero mean electric dipole moments. Yet, the water molecule is said to have a nonzero dipole moment strength $d=eΛ$ with $Λ_{H_2O} \approx 0.385\ \dot{A}$. The neutron may also be said to have an electric dipole moment strength with $Λ_{neutron} \approx 0.612\ fm$. The neutron analysis can be made experimentally consistent, if one employs a quark-diquark model of neutron structure.

hep-ph↗
arXiv2010

Impact of internal bremsstrahlung on the detection of gamma-rays from neutralinos

We present a detailed study of the effect of internal bremsstrahlung photons in the context of the minimal supersymmetric standard models and their impact on gamma-ray dark matter annihilation searches. We find that although this effect has to be included for the correct evaluation of fluxes of high energy photons from neutralino annihilation, its contribution is relevant only in models and at energies where the lines contribution is dominant over the secondary photons. Therefore, we find that the most optimistic supersymmetric scenarios for dark matter detection do not change significantly when including the internal bremsstrahlung. As an example, we review the gamma-ray dark matter detection prospects of the Draco dwarf spheroidal galaxy for the MAGIC stereoscopic system and the CTA project. Though the flux of high energy photons is enhanced by an order of magnitude in some regions of the parameter space, the expected fluxes are still much below the sensitivity of the instruments.

astro-ph.CO↗
arXiv2010

Higgs sector of the MSSM: lepton flavor violation at colliders and neutralino dark matter

We examine the prospects for the detection of Higgs mediated lepton flavor violation at LHC and at a photon collider in the minimal supersymmetric standard model with large lepton flavor violating mass insertions in the $μ-τ$ sector constraining the parameter space with several experimental bounds. We find rates probably too small to be observed at future experiments if models have to accommodate for a neutralino relic density as measured by WMAP and explain the $(g-2)_μ$ anomaly: better prospects are found if these two constraints are applied only as upper bounds. The spin-independent neutralino-nucleon cross section in the studied constrained parameter space is just below the present CDMS limit while gamma rates from neutralino annihilation in the halo are strongly suppressed.

hep-ph↗
arXiv2010

Neutralino Dark Matter and Higgs mediated Lepton Flavor Violation in the Minimal Supersymmetric Standard Model

We consider the minimal supersymmetric standard model within a scenario of large $\tanβ$ and heavy squarks and gluinos, with masses of the heavy neutral Higgs bosons below the TeV scale. We allow for the presence of a large, model independent, source of lepton flavor violation (LFV) in the slepton mass matrix in the $τ-μ$ sector by the mass insertion approximation. We constrain the parameter space using the $τ$ LFV decays together with the $B$-mesons physics observables, the anomalous magnetic moment of the muon and the dark matter relic density. We further impose the exclusion limit on spin-independent neutralino-nucleon scattering from CDMS and the recent CDF limit from direct search of the heavy neutral Higgs at the TEVATRON. We re-examine the prospects for the detection of Higgs mediated LFV at LHC, at a photon collider and in LFV decays of the $τ$ such as $τ\toμη$, $τ\toμγ$. We find rates probably too small to be observed at future experiments if models have to accommodate for the relic density measured by WMAP and explain the $(g-2)_μ$ anomaly: better prospects are found if these two constraints are applied only as upper bounds. The spin-independent neutralino-nucleon cross section in the studied constrained parameter space is just below the present CDMS limit and the running XENON100 experiment will cover the region of the parameter space where the lightest neutralino has large gaugino-higgsino mixing.

hep-ph↗
arXiv2008

Charge asymmetries in γγ\to \ell^+\ell^-+ ν's (\ell=μ, e) with polarized photons in the Standard Model

It is shown that in reaction γγ\to\ell^+\ell^-+ν's at \sqrt{s}>200 GeV with polarized photons, large and well observable differences arise in the distribution of positive and negative charged leptons (\ell=μ^\pm, e^\pm), (charge asymmetry). The modification due to the contribution of the cascade processes with intermediate τ-lepton in γγ\to W^\pm\ell^\mp + ν's reaction is taken into account. This charge asymmetry is potentially sensitive to effects of physics beyond the standard model at the anticipated luminosity of the Photon Collider mode of the future international linear collider.

hep-ph↗
arXiv2008

Supersymmetric Higgs mediated lepton flavor violation at a Photon Collider

We study a new signature of lepton flavor violation (LFV) at the Photon Collider (PC) within Supersymmetric (SUSY) theories. We consider the minimal supersymmetric standard model within a large $\tanβ$ scenario with all superpartner masses in the ${\cal O}$(TeV) while the heavy Higgs bosons masses lie below the TeV and develop sizable loop induced LFV couplings to the leptons. We consider a photon collider based on an $e^+e^-$ linear collider with $\sqrt{s}=800$ GeV with the parameters of the TESLA proposal and show that, with the expected integrated $γγ$-luminosity $L_{γγ}=200÷500$ fb$^{-1}$, the "$μτ$ fusion" mechanism is the dominant channel for the process $\gaga\toμτb\bar{b}$ providing detailed analytical and numerical studies of the signal and backgrounds. We impose on the parameter space present direct and indirect constraints from $B$ physics and rare LFV $τ$-decays and find that the LFV signal can be probed for masses of the heavy neutral Higgs bosons $A,H$ from 300 GeV up to the kinematical limit $\simeq 600$ GeV for 30$\leq\tanβ\leq$60.

hep-ph↗
arXiv2008

Instability of the Perturbation Theoretical Chromodynamic Vacuum

The standard model of strong interactions invokes the quantum chromodynamics (QCD) of quarks and gluons interacting within a fluid. At sufficiently small length scales, the effective interactions between the color charged particles within the fluid are thought to be weak. Short distance asymptotic freedom provides the perturbation theory basis for comparisons between QCD theory and laboratory high energy scattering experiments. It is here shown that the asymptotically free vacuum has negative dissipation implicit in the color electrical conductivity. Negative dissipation implies an asymptotically free QCD negative temperature {\em excited state amplifier} unstable to decay. The qualitative experimental implications of this instability are explored.

hep-th↗
arXiv2007

Klein Paradox for Optical Scattering from Excited Targets

The well known Klein paradox for the relativistic Dirac wave equation consists in the computation of possible ``negative probabilities'' induced by certain potentials in some regimes of energy. The paradox may be resolved employing the notion of electron-positron pair production in which the number of electrons present in a process can increase. The Klein paradox also exists in Maxwell's equations viewed as the wave equation for photons. In a medium containing ``inverted energy populations'' of excited atoms, e.g. in a LASER medium, one may again compute possible ``negative probabilities''. The resolution of the electromagnetic Klein paradox is that when the atoms decay, the final state may contain more photons then were contained the initial state. The optical theorem total cross section for scattering photons from excited state atoms may then be computed as negative within a frequency band with matter induced amplification.

quant-ph↗
arXiv2007

Casimir-Polder intermolecular forces in minimal length theories

Generalized uncertainty relations are known to provide a minimal length $\hbar\sqrtβ$. The effect of such minimal length in the Casimir-Polder interactions between neutral atoms (molecules) is studied. The first order correction term in the minimal uncertainty parameter is derived and found to describe an attractive potential scaling as $r^{-9}$ as opposed to the well known $r^{-7}$ long range retarded potential.

hep-th↗
arXiv2005

Two-Time Correlation Functions: Stochastic and Conventional Quantum Mechanics

An investigation of two-time correlation functions is reported within the framework of (i) Stochastic Quantum Mechanics and (ii) conventional Heisenberg-Schrödinger Quantum Mechanics. The spectral functions associated with the two-time electric dipole correlation functions are worked out in detail for the case of the hydrogen atom. While the single time averages are identical for stochastic and conventional quantum mechanics, differences arise in the two approaches for multiple time correlation functions.

quant-ph↗
arXiv2005

Testing SUSY models of lepton flavor violation at a photon collider

The loop level lepton flavor violating signals $γγ\to \ell \ell' (\ell=e,μ,τ, \ell \neq \ell^\prime)$ are studied in a scenario of low-energy, R-parity conserving, supersymmetric seesaw mechanism within the context of a high energy photon collider. Lepton flavor violation is due to off diagonal elements in the left s-lepton mass matrix induced by renormalization group equations. The average slepton masses ${\widetilde{m}}$ and the off diagonal matrix elements $Δm$ are treated as model independent free phenomenological parameters in order to discover regions in the parameter space where the signal cross section may be observable. At the energies of the $γγ$ option of the future high-energy linear collider the signal has a potentially large standard model background, and therefore particular attention is paid to the study of kinematical cuts in order to reduce the latter at an acceptable level. We find, for the ($eτ$) channel, non-negligible fractions of the parameter space ($δ_{LL}=Δm^2/\widetilde{m}^2 \gtrsim 10^{-1}$) where the statistical significance ($SS$) is $SS \gtrsim 3$.

hep-ph↗
arXiv2004

The $\bm{e^- e^-}$ mode of LC: opportunities to discover loop-level lepton flavor (number) violation

The $e^- e^-$ mode with lepton number $L=+2$ of the initial state is particularly suitable for studying lepton and flavor number violating reactions (LFV). In this brief report we give a summary of the study of two loop-level reactions which violate lepton and flavor numbers: we first consider seesaw type models with heavy Majorana neutrinos at the TeV scale and study the reactions $e^{-}e^{-} \to \ell^{-}\ell^{-}$, and then similar reactions $e^{-}e^{-} \to \ell^{-}e^{-}$ ($\ell=μ,τ$) in supersymmetric models where LFV is due to slepton mixing.

hep-ph↗
arXiv2003

Lepton flavour violation in e^{\pm}e^{-}\to \ell^{\pm}e^{-} (\ell = μ,τ) induced by R-conserving supersymmetry

The lepton flavour violating signals $e^{+}e^{-}\to \ell^{+}e^{-}$ and $e^{-}e^{-}\to \ell^{-}e^- (\ell=μ,τ)$ are studied in the context of low energy R-parity conserving supersymmetry at center of mass energies of interest for the next generation of linear colliders. Loop level amplitudes receive contributions from electroweak penguin and box diagrams involving sleptons and gauginos. Lepton flavour violation is due to off diagonal elements in $SU(2)_L$ doublet slepton mass matrix. These masses are treated as model independent free phenomenological parameters in order to discover regions in parameter space where the signal cross section may be observable. The results are compared with (a) the experimental bounds from the non-observation of rare radiative lepton decays $μ, τ\to eγ$ and (b) the general mSUGRA theoretical scenario with seesaw mechanism where off diagonal slepton matrix entries are generated by renormalization group evolution of neutrino Yukawa couplings induced by the presence of new energy scales set by the heavy $SU(2)_L$ singlet neutrino masses. It is found that in $e^- e^-$ collisions the ($eτ$) signal can be observable with a total integrated luminosity of 100 fb$^{-1}$ and the that the background can be easily suppressed. In $e^+ e^-$ collisions the cross section is smaller and higher luminosities are needed. The experimental bound on the decay $μ\to e γ$ prevents the ($eμ$) signal from being observable.

hep-ph↗