arXiv subjects

Apostolos Pilaftsis

Publications and source records attributed to Apostolos Pilaftsis.

At least 109 records · Page 6Linked to original sources

arXiv2008

B-Meson Observables in the Maximally CP-Violating MSSM with Minimal Flavour Violation

Additional sources of CP violation in the MSSM may affect B-meson mixings and decays, even in scenarios with minimal flavour violation (MFV). We formulate the maximally CP-violating and minimally flavour-violating (MCPMFV) variant of the MSSM, which has 19 parameters, including 6 phases that violate CP. We then develop a manifestly flavour-covariant effective Lagrangian formalism for calculating Higgs-mediated FCNC observables in the MSSM at large tan(beta), and analyze within the MCPMFV framework FCNC and other processes involving B mesons. We include a new class of dominant subleading contributions due to non-decoupling effects of the third-generation quarks. We present illustrative numerical results that include effects of the CP-odd MCPMFV parameters on Higgs and sparticle masses, the B_s and B_d mass differences, and on the decays B_s --> mu+ mu-, B_u --> tau nu and b --> s gamma. We use these results to derive illustrative constraints on the MCPMFV parameters imposed by D0, CDF, BELLE and BABAR measurements of B mesons, demonstrating how a potentially observable contribution to the CP asymmetry in the b --> s gamma decay may arise in the MSSM with MCPMFV.

hep-ph↗

arXiv2008

Supersymmetric Higgs Singlet Effects on B-Meson FCNC Observables at Large tan(beta)

Higgs singlet superfields are usually present in most extensions of the Minimal Supersymmetric Standard Model (MSSM) that address the mu-problem, such as the Next-to-Minimal Supersymmetric Standard Model (NMSSM) and the Minimal Nonminimal Supersymmetric Standard Model (MNSSM). Employing a gauge- and flavour-covariant effective Lagrangian formalism, we show how the singlet Higgs bosons of such theories can have significant contributions to B-meson flavour-changing neutral current (FCNC) observables for large values of $\tanβ\stackrel{>}{{}_\sim} 50$ at the 1-loop level. Illustrative results are presented including effects on the B_s and B_d mass differences and on the rare decay $B_s\toμ^+μ^-$. In particular, we find that depending on the actual value of the lightest singlet pseudoscalar mass in the NMSSM, the branching ratio for $B_s\toμ^+μ^-$ can be enhanced or even suppressed with respect to the Standard Model prediction by more than one order of magnitude.

hep-ph↗

arXiv2008

Resonant CP Violation due to Heavy Neutrinos at the LHC

The observed light neutrinos may be related to the existence of new heavy neutrinos in the spectrum of the SM. If a pair of heavy neutrinos has nearly degenerate masses, then CP violation from the interference between tree-level and self-energy graphs can be resonantly enhanced. We explore the possibility of observing CP asymmetries due to this mechanism at the LHC. We consider a pair of heavy neutrinos N_{1,2} with masses ranging from 100 to 500 GeV and a mass-splitting Δm_N = m_{N_2}-m_{N_1} comparable to their widths Γ_{N_{1,2}}. We find that for Δm_N ~ Γ_{N_{1,2}}, the resulting CP asymmetries can be very large or even maximal and therefore, could potentially be observed at the LHC.

hep-ph↗

arXiv2008

Textures and Semi-Local Strings in SUSY Hybrid Inflation

Global topological defects may account for the large cold spot observed in the Cosmic Microwave Background. We explore possibilities of constructing models of supersymmetric F-term hybrid inflation, where the waterfall fields are globally SU(2)-symmetric. In contrast to the case where SU(2) is gauged, there arise Goldstone bosons and additional moduli, which are lifted only by masses of soft-supersymmetry breaking scale. The model predicts the existence of global textures, which can become semi-local strings if the waterfall fields are gauged under U(1)_X. Gravitino overproduction can be avoided if reheating proceeds via the light SU(2)-modes or right-handed sneutrinos. For values of the inflaton- waterfall coupling >=10^-4, the symmetry breaking scale imposed by normalisation of the power spectrum generated from inflation coincides with the energy scale required to explain the most prominent of the cold spots. In this case, the spectrum of density fluctuations is close to scale-invariant which can be reconciled with measurements of the power spectrum by the inclusion of the sub-dominant component due to the topological defects.

hep-ph↗

arXiv2008

Electroweak Resonant Leptogenesis in the Singlet Majoron Model

We study resonant leptogenesis at the electroweak phase transition in the singlet Majoron model with right-handed neutrinos. We consider a scenario, where the SM gauge group and the lepton number break down spontaneously during a second-order electroweak phase transition. We calculate the flavour- and temperature-dependent leptonic asymmetries, by including the novel contributions from the transverse polarisations of the W+/- and Z bosons. The required resummation of the gauge-dependent off-shell heavy-neutrino self-energies is consistently treated within the gauge-invariant framework of the Pinch Technique. Taking into consideration the freeze-out dynamics of sphalerons, we delineate the parameter space of the model that is compatible with successful electroweak resonant leptogenesis. The phenomenological and astrophysical implications of the model are discussed.

hep-ph↗

arXiv2008

Comments on Spontaneous Spin-Statistics Violation by Fermion Condensates

Scalar condensation, the well-established Higgs phenomenon, is the standard paradigm for building up renormalizable gauge-invariant theories of massive gauge bosons. In this short note, we demonstrate the uniqueness of the Higgs vacuum state under the possible presence of fermion condensates in a renormalizable U(1) model. In the same context, we explain why spontaneous spin-statistics violation is technically not admitted in conventional Quantum Field Theory.

hep-ph↗

arXiv2007

Radiative Yukawa Couplings for Supersymmetric Higgs Singlets at Large tan(beta)

Singlet Higgs bosons present in extensions of the MSSM can have sizable Yukawa couplings to the b quark and the tau lepton for large values of tan(beta) at the 1-loop level. We present an effective Lagrangian which incorporates these tan(beta)-enhanced Yukawa couplings and which enables us to study their effect on singlet Higgs-boson phenomenology within the context of both the mnSSM and the NMSSM. In particular, we find that the loop-induced coupling can be a significant effect for the singlet pseudoscalar, and may dominate its decay modes. Further implications of the tan(beta)-enhanced Yukawa couplings for the phenomenology of the singlet Higgs bosons are briefly discussed.

hep-ph↗

arXiv2006

Anatomy of F_D-Term Hybrid Inflation

We analyze the cosmological implications of F-term hybrid inflation with a subdominant Fayet--Iliopoulos D-term whose presence explicitly breaks a D-parity in the inflaton-waterfall sector. This scenario of inflation, which is called F_D-term hybrid model for brevity, can naturally predict lepton number violation at the electroweak scale, by tying the mu-parameter of the MSSM to an SO(3)-symmetric Majorana mass m_N, via the vacuum expectation value of the inflaton field. We show how a negative Hubble-induced mass term in a next-to-minimal extension of supergravity helps to accommodate the present CMB data and considerably weaken the strict constraints on the theoretical parameters, resulting from cosmic string effects on the power spectrum P_R. The usual gravitino overabundance constraint may be significantly relaxed in this model, once the enormous entropy release from the late decays of the ultraheavy waterfall gauge particles is properly considered. As the Universe enters a second thermalization phase involving a very low reheat temperature, which might be as low as about 0.3 TeV, thermal electroweak-scale resonant leptogenesis provides a viable mechanism for successful baryogenesis, while thermal right-handed sneutrinos emerge as new possible candidates for solving the cold dark matter problem. In addition, we discuss grand unified theory realizations of F_D-term hybrid inflation devoid of cosmic strings and monopoles, based on the complete breaking of an SU(2) subgroup. The F_D-term hybrid model offers rich particle-physics phenomenology, which could be probed at high-energy colliders, as well as in low-energy experiments of lepton flavour or number violation.

hep-ph↗

arXiv2006

Higgs Phenomenology with CPsuperH

The MSSM contains CP-violating phases that may have important observable effects in Higgs physics. We review recent highlights in Higgs phenomenology obtained with the code CPsuperH, a useful tool for studies of the production, mixing and decay of a coupled system of the neutral Higgs bosons at future high energy colliders such as the LHC, ILC ($γ$LC), and a muon collider (MC). CPsuperH implements the constraints from upper limits on electric dipole moments, and may be extended to include other related low-energy observables, such as b -> s γand B -> K l l, and to compute the relic abundance of the lightest neutralino.

hep-ph↗

arXiv2006

F_D-Term Hybrid Inflation with Electroweak-Scale Lepton Number Violation

We study F-term hybrid inflation in a novel supersymmetric extension of the SM with a subdominant Fayet-Iliopoulos D-term. We call this particular form of inflation, in short, F_D-term hybrid inflation. The proposed model ties the mu-parameter of the MSSM to an SO(3)-symmetric Majorana mass m_N, through the vacuum expectation value of the inflaton field. The late decays of the ultraheavy particles associated with the extra U(1) gauge group, which are abundantly produced during the preheating epoch, could lower the reheat temperature even up to 1 TeV, thereby avoiding the gravitino overproduction problem. The baryon asymmetry in the Universe can be explained by thermal electroweak-scale resonant leptogenesis, in a way independent of any pre-existing lepton- or baryon-number abundance. Further cosmological and particle-physics implications of the F_D-term hybrid model are briefly discussed.

hep-ph↗

arXiv2005

Displacement Operator Formalism

We review the D-formalism, a new method for determining the renormalization of Green functions to all orders in perturbation theory. This formalism exploits the fact that the renormalized Green functions may be calculated by displacing by an infinite amount the renormalized fields and parameters of the theory with respect to the unrenormalized ones. We briefly discuss some of its main characteristics, its conceptual and practical advantages, and some new results obtained through it.

hep-ph↗

arXiv2005

Electroweak-Scale Resonant Leptogenesis

We study minimal scenarios of resonant leptogenesis near the electroweak phase transition. These models offer a number of testable phenomenological signatures for low-energy experiments and future high-energy colliders. Our study extends previous analyses of the relevant network of Boltzmann equations, consistently taking into account effects from out of equilibrium sphalerons and single lepton flavours. We show that the effects from single lepton flavours become very important in variants of resonant leptogenesis, where the observed baryon asymmetry in the Universe is created by lepton-to-baryon conversion of an individual lepton number, for example that of the tau lepton. The predictions of such resonant tau-leptogenesis models for the final baryon asymmetry are almost independent of the initial lepton-number and heavy neutrino abundances. These models accommodate the current neutrino data and have a number of testable phenomenological implications. They contain electroweak-scale heavy Majorana neutrinos with appreciable couplings to electrons and muons, which can be probed at future e+ e- and mu+ mu- high-energy colliders. In particular, resonant tau-leptogenesis models predict sizeable 0νββdecay, as well as e- and mu-number-violating processes, such as mu -> e gamma and mu -> e conversion in nuclei, with rates that are within reach of the experiments proposed by the MEG and MECO collaborations.

hep-ph↗

arXiv2005

Resonant CP Violation in Higgs Radiation at e^+e^- Linear Collider

We study resonant CP violation in the Higgsstrahlung process e^+e^- -> H_{1,2,3} (Z -> e^+e^-, μ^+μ^-) and subsequent decays H_{1,2,3} -> b \bar{b}, τ^-τ^+, in the MSSM with Higgs-sector CP violation induced by radiative corrections. At a high-energy e^+e^- linear collider, the recoil-mass method enables one to determine the invariant mass of a fermion pair produced by Higgs decays with a precision as good as 1 GeV. Assuming an integrated luminosity of 100/fb, we show that the production lineshape of a coupled system of neutral Higgs bosons decaying into b\bar{b} quarks is sensitive to the CP-violating parameters. When the Higgs bosons decay into τ^-τ^+, two CP asymmetries can be defined using the longitudinal and transverse polarizations of the tau leptons. Taking into account the constraints from electric dipole moments, we find that these CP asymmetries can be as large as 80 %, in a tri-mixing scenario where all three neutral Higgs states of the MSSM are nearly degenerate and mix significantly.

hep-ph↗

arXiv2005

Heavy Majorana Neutrino Production at e- gamma Colliders

We study signatures of heavy Majorana neutrinos at e- gamma colliders. Since these particles violate lepton number, they can give rise to the reactions e- gamma -> W- W- e+ and e- gamma -> W+ mu- mu- nu. The Standard Model background contains extra light neutrinos that escape detection, and can be reduced significantly after imposing appropriate kinematical cuts. We analyze the physics potential of an e- gamma collider, with centre of mass energies sqrt(s) = 0.5--1 TeV and a total integrated luminosity of 100/fb, for detecting heavy Majorana neutrinos with masses mN = 100--400 GeV. Assuming that heavy neutrinos couple predominantly to one lepton flavour at a time, we find that 10 expected background-free events can be established for |B_{eN}| >~ 4.6 x 10^{-3}. Instead, if no signal is observed, this will imply that |B_{eN}| ~< 2.7 x 10^{-3} and |B_{μN}| ~< 0.05 at the 90% confidence level.

hep-ph↗

arXiv2005

Resonant τ-Leptogenesis with Observable Lepton Number Violation

We consider a minimal extension of the Standard Model with one singlet neutrino per generation that can realize resonant leptogenesis at the electroweak scale. In particular, the baryon asymmetry in the Universe can be created by resonant lepton-to-baryon conversion of an individual lepton number, for example that of the $τ$-lepton. The solar and atmospheric neutrino data can be explained by a simple CP-violating Yukawa texture. The model has several testable phenomenological implications. Most interestingly, it predicts heavy Majorana neutrinos at the sub-TeV scale, which can be probed at $e^+e^-$ linear colliders, as well as $e$- and $μ$-lepton-number-violating processes, such as $0νββ$ decay and $μ\to eγ$, with rates that are within reach of experimental sensitivity.

hep-ph↗

arXiv2005

Resonant CP Violation in MSSM Higgs Production and Decay at $γγ$ Colliders

We study CP-violating phenomena in the production, mixing and decay of a coupled system of CP-violating neutral Higgs bosons at γγcolliders, assuming a Minimal Supersymmetric Standard Model (MSSM) Higgs sector in which CP violation is radiatively induced by phases in the soft supersymmetry-breaking gaugino masses and third-generation trilinear squark couplings. We discuss CP asymmetries in the production and decays of μ^+ μ^-, τ^+ τ^-, {\bar b} b and {\bar t} t pairs. We find large asymmetries when two (or all three) neutral Higgs bosons are nearly degenerate with mass differences comparable to their decay widths, as happens naturally in the CP-violating MSSM for values of \tanβ>~ 5(30) and large (small) charged Higgs-boson masses.

hep-ph↗

arXiv2005

Diffraction as a CP and Lineshape Analyzer for MSSM Higgs Bosons at the LHC

We study the production and decay of a coupled system of mixed neutral MSSM Higgs bosons in exclusive double-diffractive processes at the LHC, including non-vanishing CP phases in the soft supersymmetry-breaking gaugino masses and third-generation trilinear squark couplings. The three neutral Higgs bosons are naturally nearly degenerate, for large values of \tanβ, when the charged Higgs boson weighs around 150 GeV. Large mixing between all three neutral Higgs bosons is possible when CP is violated, a three-way mixing scenario which we also term tri-mixing. A resolution in the Higgs mass of \sim 1 GeV, which may be achievable using the missing-mass method, would allow one to distinguish nearly degenerate Higgs bosons by studying the production lineshape. Measurements of the polarizations of the tau leptons coming from the Higgs-boson decays could offer a direct and observable signal of CP violation in the Higgs sector.

hep-ph↗

arXiv2005

Quantization and High Energy Unitarity of 5D Orbifold Theories with Brane Kinetic Terms

Five-dimensional field theories compactified on an S^1/Z_2 orbifold naturally include local brane kinetic terms at the orbifold fixed points at the tree as well as the quantum level. We study the quantization of these theories before the Kaluza--Klein reduction and derive the relevant Ward and Slavnov-Taylor identities that result from the underlying gauge and Becchi-Rouet-Stora symmetries of the theory. With the help of these identities, we obtain a generalization of the equivalence theorem, where the known high-energy equivalence relation between the longitudinal Kaluza-Klein gauge modes and their respective would-be Goldstone bosons is extended to consistently include the energetically suppressed terms in the high-energy scatterings. Demanding perturbative unitarity, we compute upper limits on the number of the Kaluza-Klein modes. We find that these limits weakly depend on the size of the brane kinetic terms.

hep-ph↗