arXiv subjects

Alessandro Strumia

Publications and source records attributed to Alessandro Strumia.

At least 181 records · Page 10Linked to original sources

arXiv2003

Brane to brane gravity mediation of supersymmetry breaking

We extend the results of Mirabelli and Peskin to supergravity. We study the compactification on S_1/Z_2 of Zucker's off-shell formulation of 5D supergravity and its coupling to matter at the fixed points. We clarify some issues related to the off-shell description of supersymmetry breaking a la Scherk-Schwarz (here employed only as a technical tool) discussing how to deal with singular gravitino wave functions. We then consider `visible' and `hidden' chiral superfields localized at the two different fixed points and communicating only through 5D supergravity. We compute the one-loop corrections that mix the two sectors and the radion superfield. Locality in 5D ensures the calculability of these effects, which transmit supersymmetry breaking from the hidden to the visible sector. In the minimal set-up visible-sector scalars get a universal squared mass m_0^2 < 0. In general (e.g. in presence of a sizable gravitational kinetic term localized on the hidden brane) the radion-mediated contribution to m_0^2 can be positive and dominant. Although we did not build a complete satisfactory model, brane-to-brane effects can cure the tachyonic sleptons predicted by anomaly mediation by adding a positive m_0^2 which is universal up to subleading flavour-breaking corrections.

hep-th↗

arXiv2003

Neutrino anomalies

Solar and atmospheric evidences have been established and can be explained by neutrino masses. Furthermore, other experiments claim a few unconfirmed neutrino anomalies. We critically reanalyze the 0nu2beta, LSND and NuTeV anomalies.

hep-ex↗

arXiv2003

Precise quasielastic neutrino/nucleon cross section

Quasielastic antineutrino/proton and neutrino/neutron scatterings can be well approximated by simple formulae, valid around MeV or GeV energies. We obtain a single expression valid in the whole range, and discuss its relevance for studies of supernova neutrinos, which reach intermediate energies.

astro-ph↗

arXiv2003

Interpreting the LSND anomaly: sterile neutrinos or CPT-violation or...?

We first study how sterile neutrinos can fit the 5sigma bar-nu_mu --> bar-nu_e LSND anomaly: 2+2 solutions are strongly disfavoured by solar and atmospheric data, while 3+1 solutions can still give a poor fit (for a specific range of oscillation parameters, to be tested by MiniBooNE). If instead MiniBoone will find no nu_mu --> nu_e signal, we will have a hint for CPT violation. Already now, unlike sterile neutrinos, CPT-violating neutrino masses can nicely accomodate all safe and unsafe data. We study how much CPT must be conserved according to atmospheric and K2K data and list which CPT-violating signals could be discovered by forthcoming solar and long-baseline experiments.

hep-ph↗

arXiv2003

Constraints on extra-dimensional theories from virtual-graviton exchange

We study the effective interactions induced by loops of extra-dimensional gravitons and show the special role of a specific dimension-6 four-fermion operator, product of two flavour-universal axial currents. By introducing an ultraviolet cut-off, we compare the present constraints on low-scale quantum gravity from various processes involving real-graviton emission and virtual-graviton exchange. The LEP2 limits on dimension-6 four-fermion interactions give one of the strongest constraint on the theory, in particular excluding the case of strongly-interacting gravity at the weak scale.

hep-ph↗

arXiv2002

Non standard analysis of the solar neutrino anomaly (updated including the SNO day/night spectral data)

Continuing previous work, a model independent analysis of the solar neutrino anomaly is performed in terms of neutrino oscillations, allowing a comparison with the predictions of the Standard Solar Model. SMA and LMA solutions emerge also in this case, although somewhat different from the standard ones. The significance of the NC/CC double ratio measurable in SNO is illustrated in this context.

hep-ph↗

arXiv2002

Which solar neutrino data favour the LMA solution?

Assuming neutrino oscillations, global analyses of solar data find that the LOW solution is significantly disfavoured, leaving LMA as the best solution. But the preference for LMA rests on three weak hints: the spectrum of earth matter effects (Super-Kamiokande sees an overall day/night asymmetry only at 1 sigma), the Cl rate (but LMA and LOW predictions are both above the measured value), the Ga rate (newer data decrease towards the LOW predictions both in GNO and SAGE). Only new data will tell us if LMA is the true solution.

hep-ph↗

arXiv2001

Electron and muon electric dipoles in supersymmetric scenarios

We study if a sizeable muon electric dipole can arise in supersymmetric frameworks able to account for the tight experimental bounds on sfermion masses, like an appropriate flavor symmetry, or like a flavor-blind mechanism of SUSY breaking (in presence of radiative corrections charchteristic of GUT models, or due to Yukawa couplings of neutrinos in see-saw models). In some cases it is possible to evade the naive scaling d_mu/d_e = m_mu/m_e and obtain a d_mu as large as 10^{-22--23} e cm. In most cases d_mu is around 10^{-24--25} e cm and (d_mu/d_e)/(m_mu/m_e) is only slightly different from one: this ratio contains interesting informations on the source of the dipoles and on the texture of the lepton Yukawa matrix. We also update GUT predictions for mu --> e gamma and related processes.

hep-ph↗

arXiv2001

Collider signals of brane fluctuations

Assuming that we live on a non rigid brane with TeV-scale tension, the scalar fields that control the coordinates of our brane in the extra dimensions give rise to missing energy signals at high-energy colliders with a characteristic angular and energy spectrum, identical to the one due to graviton emission in 6 extra dimensions. LEP bounds and LHC capabilities are analyzed.

hep-ph↗

arXiv2001

Phenomenological implications of neutrinos in extra dimensions

Standard Model singlet neutrinos propagating in extra dimensions induce small Dirac neutrino masses. While it seems rather unlikely that their Kaluza-Klein excitations directly participate in the observed neutrino oscillations, their virtual exchange may lead to detectable signatures in future neutrino experiments and in rare charged lepton processes. We show how these effects can be described by specific dimension-six effective operators and discuss their experimental signals.

hep-ph↗

arXiv2001

Which solar neutrino experiment after KamLAND and Borexino?

We estimate how well we will know the parameters of solar neutrino oscillations after KamLAND and Borexino. The expected error on Delta m^2 is few per-mille in the VO and QVO regions, few per-cent in the LMA region, and around 10% in the LOW region. The expected error on sin^2 2theta is around 5%. KamLAND and Borexino will tell unambiguously which specific new measurement, dedicated to pp solar neutrinos, is able to contribute to the determination of theta and perhaps of Delta m^2. The present data suggest as more likely outcomes: no measurement, or the total pp rate, or its day/night variation.

hep-ph↗

arXiv2001

On the metastability of the Standard Model vacuum

If the Higgs mass m_H is as low as suggested by present experimental information, the Standard Model ground state might not be absolutely stable. We present a detailed analysis of the lower bounds on m_H imposed by the requirement that the electroweak vacuum be sufficiently long-lived. We perform a complete one-loop calculation of the tunnelling probability at zero temperature, and we improve it by means of two-loop renormalization-group equations. We find that, for m_H=115 GeV, the Higgs potential develops an instability below the Planck scale for m_t>(166\pm 2) GeV, but the electroweak vacuum is sufficiently long-lived for m_t < (175\pm 2) \GeV.

hep-ph↗

arXiv2000

The `LEP paradox'

Is there a Higgs? Where is it? Is supersymmetry there? Where is it? By discussing these questions, we call attention to the `LEP paradox', which is how we see the naturalness problem of the Fermi scale after a decade of electroweak precision measurements, mostly done at LEP.

hep-ph↗

arXiv2000

Are heavy scalars natural in minimal supergravity?

It has been recently claimed that very large values of a universal soft mass term m_0 for sfermions and higgs bosons become natural when M_top is close to 175 GeV if tanβ\approx 10. We show that very large values of m_0 require accidental cancellations not guaranteed by experimental data or theoretical assumptions, and consequently an unnatural fine-tuning of the parameters.

hep-ph↗

arXiv2000

Relating m_Higgs to m_SUSY by a loop factor

We assume that the scale of the soft supersymmetry breaking masses, m_SUSY, sliding at tree level, is fixed by the minimization of the potential, but without a significant contribution of the cosmological term. Under these assumptions the electroweak breaking scale gets related to m_SUSY by a loop factor. Applied to specific models of supersymmetry breaking, this mechanism naturally gives sparticles slightly above all present accelerator bounds.

hep-ph↗

arXiv2000

Neutrino oscillations and large extra dimensions

Assuming that right-handed neutrinos exist and propagate in some large extra dimensions, we attempt to give a comprehensive description of the phenomenology of neutrino oscillations. A few alternative explanations of the atmospheric neutrino anomaly emerge, different from the standard nuMu --> nuTau or nuMu --> nuSterile interpretations. Constraints from nucleosynthesis and supernova 1987a are discussed. The constraints from SN1987a indicates a maximum radius of any extra dimension of about 1 Angstrom.

hep-ph↗

arXiv1999

Phenomenology of deflected anomaly-mediation

We explore the phenomenology of a class of models with anomaly-mediated supersymmetry breaking. These models retain the successful flavor properties of the minimal scenario while avoiding the tachyons. The mass spectrum is predicted in terms of a few parameters. However various qualitatively different spectra are possible, often strongly different from the ones usually employed to explore capabilities of new accelerators. One stable feature is the limited spread of the spectrum, so that squarks and gluinos could be conceivably produced at TEVII. The lightest superpartner of standard particles is often a charged slepton or a neutral higgsino. It behaves as a stable particle in collider experiments but it decays at or before nucleosynthesis. We identify the experimental signatures at hadron colliders that can help distinguish this scenario from the usual ones.

hep-ph↗

arXiv1999

Bubble-nucleation rates for cosmological phase transitions

We estimate bubble-nucleation rates for cosmological phase transitions. We concentrate on the evaluation of the pre-exponential factor, for which we give approximate analytical expressions. Our approach relies on the use of a real coarse-grained potential. We show how the coarse-graining scale can be determined in the studies of high-temperature phase transitions. We discuss the metastability bound on the Higgs-boson mass and the electroweak phase transition. We find that the saddle-point approximation is reliable in the first case and breaks down in the second case.

hep-ph↗