arXiv subjects

Maxim Pospelov

Publications and source records attributed to Maxim Pospelov.

At least 181 records · Page 10Linked to original sources

arXiv2006

Sensitivity to new supersymmetric thresholds through flavour and CP violating physics

Treating the MSSM as an effective theory below a threshold scale Lambda, we study the consequences of having dimension-five operators in the superpotential for flavour and CP-violating processes. Below the supersymmetric threshold such terms generate flavour changing and/or CP-odd effective operators of dimension six composed from the Standard Model fermions, that have the interesting property of decoupling linearly with the threshold scale, i.e. as 1/(Lambda m_soft), where m_soft is the scale of soft supersymmetry breaking. The assumption of weak-scale supersymmetry, together with the stringent limits on electric dipole moments and lepton flavour-violating processes, then provides sensitivity to Lambda as high as 10^7-10^9 GeV. We discuss the varying sensitivity to these scales within several MSSM benchmark scenarios and also outline the classes of UV physics which could generate these operators.

hep-ph↗

arXiv2005

Flavor and CP violating physics from new supersymmetric thresholds

Treating the MSSM as an effective theory, we study the implications of having dimension five operators in the superpotential for flavor and CP-violating processes, exploiting the linear decoupling of observable effects with respect to the new threshold scale Λ. We show that the assumption of weak scale supersymmetry, when combined with the stringent limits on electric dipole moments and lepton flavor-violating processes, provides sensitivity to Λas high as 10^7-10^9 GeV, while the next generation of experiments could directly probe the high-energy scales suggested by neutrino physics.

hep-ph↗

arXiv2005

Electric dipole moments as probes of new physics

We review several aspects of flavour-diagonal CP violation, focussing on the role played by the electric dipole moments (EDMs) of leptons, nucleons, atoms and molecules, which consitute the source of several stringent constraints on new CP-violating physics. We dwell specifically on the calculational aspects of applying the hadronic EDM constraints, reviewing in detail the application of QCD sum-rules to the calculation of nucleon EDMs and CP-odd pion-nucleon couplings. We also consider the current status of EDMs in the Standard Model, and on the ensuing constraints on the underlying sources of CP-violation in physics beyond the Standard Model, focussing on weak-scale supersymmetry.

hep-ph↗

arXiv2005

CP-odd Phase Correlations and Electric Dipole Moments

We revisit the constraints imposed by electric dipole moments (EDMs) of nucleons and heavy atoms on new CP-violating sources within supersymmetric theories. We point out that certain two-loop renormalization group corrections induce significant mixing between the basis-invariant CP-odd phases. In the framework of the constrained minimal supersymmetric standard model (CMSSM), the CP-odd invariant related to the soft trilinear A-phase at the GUT scale, theta_A, induces non-trivial and distinct CP-odd phases for the three gaugino masses at the weak scale. The latter give one-loop contributions to EDMs enhanced by tan beta, and can provide the dominant contribution to the electron EDM induced by theta_A. We perform a detailed analysis of the EDM constraints within the CMSSM, exhibiting the reach, in terms of sparticle spectra, which may be obtained assuming generic phases, as well as the limits on the CP-odd phases for some specific parameter points where detailed phenomenological studies are available. We also illustrate how this reach will expand with results from the next generation of experiments which are currently in development.

hep-ph↗

arXiv2005

Lorentz Violating Supersymmetric Quantum Electrodynamics

Theory of Supersymmetric Quantum Electrodynamics is extended by interactions with external vector and tensor backgrounds, that are assumed to be generated by some Lorentz-violating (LV) dynamics at an ultraviolet scale perhaps related to the Planck scale. Exact supersymmetry requires that such interactions correspond to LV operators of dimension five or higher, providing a solution to the naturalness problem in the LV sector. We classify all dimension five and six LV operators, analyze their properties at the quantum level and describe observational consequences of LV in this theory. We show that LV operators do not induce destabilizing D-terms, gauge anomaly and the Chern-Simons term for photons. We calculate the renormalization group evolution of dimension five LV operators and their mixing with dimension three LV operators, controlled by the scale of the soft-breaking masses. Dimension five LV operators are constrained by the low-energy precision measurements at 10^{-10}-10^{-5} level in units of the inverse Planck scale, while the Planck-scale suppressed dimension six LV operators are allowed by observational data.

hep-ph↗

arXiv2005

Theta Vacua, QCD Sum Rules, and the Neutron Electric Dipole Moment

We present a detailed study of the electric dipole moment of the neutron induced by a vacuum theta angle within the framework of QCD sum rules. At next-to-next-to leading order in the operator product expansion, we find the result d_n(θ) = 2.4 x 10^{-16} θe cm, to approximately 40% precision. With the current experimental bound this translates into a limit on the theta parameter of |θ| < 3 x 10^{-10}. We compare this result with the long-standing estimates obtained within chiral perturbation theory, and observe a numerical similarity, but also significant differences in the source of the dominant contribution.

hep-ph↗

arXiv2005

Neutron EDM from Electric and Chromoelectric Dipole Moments of Quarks

Using QCD sum rules, we calculate the electric dipole moment of the neutron d_n induced by all CP violating operators up to dimension five. We find that the chromoelectric dipole moments of quarks \tilde d_i, including that of the strange quark, provide significant contributions comparable in magnitude to those induced by the quark electric dipole moments d_i. When the theta term is removed via the Peccei-Quinn symmetry, the strange quark contribution is also suppressed and d_n =(1\pm 0.5)[1.1e(\tilde d_d + 0.5\tilde d_u)+1.4(d_d-0.25d_u)].

hep-ph↗

arXiv2005

Ghosts and Tachyons in the Fifth Dimension

We present several solutions for the five dimensional gravity models in the presence of bulk ghosts and tachyons to argue that these "troublesome" fields can be a useful model-building tool. The ghost-like signature of the kinetic term for a bulk scalar creates a minimum in the scale factor, removing the necessity for a negative tension brane in models with the compactified fifth dimension. It is shown that the model with the positive tension branes and a ghost field in the bulk leads to the radion stabilization. The bulk scalar with the variable sign kinetic term can be used to model both positive and negative tension branes of a finite width in the compact dimension. Finally, we present several ghost and tachyon field configurations in the bulk that lead to the localization of gravity in four dimensions, including one solution with the Gaussian profile for the metric, g_{μν}(y)=η_{μν}\exp{-αy^2}, which leads to a stronger localization of gravity than the Randall-Sundrum model.

hep-ph↗

arXiv2005

Lorentz Violation in Supersymmetric Field Theories

We construct supersymmetric Lorentz violating operators for matter and gauge fields. We show that in the supersymmetric Standard Model the lowest possible dimension for such operators is five, and therefore they are suppressed by at least one power of an ultra--violet energy scale, providing a possible explanation for the smallness of Lorentz violation and its stability against radiative corrections. Supersymmetric Lorentz noninvariant operators do not lead to modifications of dispersion relations at high energies thereby escaping constraints from astrophysical searches for Lorentz violation.

hep-ph↗

arXiv2004

Unstable Relics as a Source of Galactic Positrons

We calculate the fluxes of 511 KeV photons from the Galactic bulge caused by positrons produced in the decays of relic particles with masses less than 100 MeV. In particular, we tighten the constraints on sterile neutrinos over a large domain of the mass--mixing angle parameter space, where the resulting photon flux would significantly exceed the experimental data. At the same time, the observed photon fluxes can be easily caused by decaying sterile neutrinos in the mass range 1 MeV < m_sterile < 50 MeV with the cosmological abundance typically within 10^{-9} < Omega_sterile < 10^{-5}, assuming that Omega_sterile comes entirely from the conversion of active neutrinos in the early Universe. Other candidates for decaying relics such as neutral (pseudo)scalar particles coupled to leptons with the gravitational strength can be compatible with the photon flux, and can constitute the main component of cold dark matter.

hep-ph↗

arXiv2004

Search for Dark Matter in b -> s Transitions with Missing Energy

Dedicated underground experiments searching for dark matter have little sensitivity to GeV and sub-GeV masses of dark matter particles. We show that the decay of B mesons to K(K^*) and missing energy in the final state can be an efficient probe of dark matter models in this mass range. We analyze the minimal scalar dark matter model to show that the width of the decay mode with two dark matter scalars B\to KSS may exceed the decay width in the Standard Model channel, B\to Kν\barν, by up to two orders of magnitude. Existing data from B physics experiments almost entirely exclude dark matter scalars with masses less than 1 GeV. Expected data from B factories will probe the range of dark matter masses up to 2 GeV.

hep-ph↗

arXiv2004

Electric Dipole Moments of Leptons in the Presence of Majorana Neutrinos

We calculate the two-loop diagrams that give a non-zero contribution to the electric dipole moment d_l of a charged lepton l due to possible Majorana masses of neutrinos. Using the example with one generation of the Standard Model leptons and two heavy right-handed neutrinos, we demonstrate that the non-vanishing result for d_l first appears in order O(m_l m_ν^2 G_F^2), where m_νis the mass of the light neutrino and the see-saw type relation is imposed. This effect is beyond the reach of presently planned experiments.

hep-ph↗

arXiv2004

Quintessence Models and the Cosmological Evolution of alpha

The cosmological evolution of a quintessence-like scalar field, phi, coupled to matter and gauge fields leads to effective modifications of the coupling constants and particle masses over time. We analyze a class of models where the scalar field potential V(phi) and the couplings to matter B(phi) admit common extremum in phi, as in the Damour-Polyakov ansatz. We find that even for the simplest choices of potentials and B(phi), the observational constraints on delta alpha/alpha coming from quasar absorption spectra, the Oklo phenomenon and Big Bang nucleosynthesis provide complementary constraints on the parameters of the model. We show the evolutionary history of these models in some detail and describe the effects of a varying mass for dark matter.

astro-ph↗

arXiv2004

Probing CP Violation with the Deuteron Electric Dipole Moment

We present an analysis of the electric dipole moment (EDM) of the deuteron as induced by CP-violating operators of dimension 4, 5 and 6 including theta QCD, the EDMs and color EDMs of quarks, four-quark interactions and the Weinberg operator. We demonstrate that the precision goal of the EDM Collaboration's proposal to search for the deuteron EDM, (1-3)\times 10^{-27} e cm, will provide an improvement in sensitivity to these sources of one-two orders of magnitude relative to the existing bounds. We consider in detail the level to which CP-odd phases can be probed within the MSSM.

hep-ph↗

arXiv2004

Experimental Challenges for Quantum Gravity

The existence of a new fundamental scale may lead to modified dispersion relations for particles at high energies. Such modifications seem to be realized with the Planck scale in certain descriptions of quantum gravity. We apply effective field theory to this problem and identify dimension 5 operators that would lead to cubic modifications of dispersion relations for Standard Model particles. We also discuss other issues related to this approach including various experimental bounds on the strength of these interactions. Further we sketch a scenario where mixing of these operators with dimensions 3 and 4 due to quantum effects is minimal.

gr-qc↗

arXiv2003

Electric Dipole Moments in the MSSM at Large tan(beta)

Within the minimal supersymmetric standard model (MSSM), the large tan(beta) regime can lead to important modifications in the pattern of CP-violating sources contributing to low energy electric dipole moments (EDMs). In particular, four-fermion CP-violating interactions induced by Higgs exchange should be accounted for alongside the constituent EDMs of quarks and electrons. To this end, we present a comprehensive analysis of three low energy EDM observables - namely the EDMs of thallium, mercury and the neutron - at large tan(beta), in terms of one- and two-loop contributions to the constituent EDMs and four-fermion interactions. We concentrate on the constrained MSSM as well as the MSSM with non-universal Higgs masses, and include the CP-violating phases of mu and A. Our results indicate that the atomic EDMs receive significant corrections from four-fermion operators, especially when Im(A) is the only CP-violating source, whereas the neutron EDM remains relatively insensitive to these effects. As a consequence, in a large portion of the parameter space, one cannot infer a separate bound on the electron EDM via the experimental constraint on the thallium EDM. Furthermore, we find that the electron EDM can be greatly reduced due to the destructive interference of one- and two-loop contributions with the latter being dominated by virtual staus.

hep-ph↗

arXiv2003

A Re-examination of the $^{187}$Re Bound on the Variation of Fundamental Couplings

We reconsider the Re187 bound on the variation of the fine-structure constant. We combine the meteoritic measurement with several present-day lab measurements to firmly establish the quantitative upper limit to the time variation over the age of the solar system. We find that the relative change of the fine-structure constant between its present value and $α$ of \sim 4.6 Gyr ago is consistent with zero, Delta alpha/alpha = [-8\pm 8 (1σ)] x 10^{-7}. We also rederive this bound in models where all gauge and Yukawa couplings vary in an interdependent manner, as would be expected in unified theories.

astro-ph↗

arXiv2003

Ultraviolet modifications of dispersion relations in effective field theory

The existence of a fundamental ultraviolet scale, such as the Planck scale, may lead to modifications of the dispersion relations for particles at high energies, in some scenarios of quantum gravity. We apply effective field theory to this problem and identify dimension 5 operators that do not mix with dimensions 3 and 4 and lead to cubic modifications of dispersion relations for scalars, fermions, and vector particles. Further we show that, for electrons, photons and light quarks, clock comparison experiments bound these operators at 10^{-5}/Mpl.

hep-ph↗