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D. S. Gorbunov

Publications and source records attributed to D. S. Gorbunov.

At least 55 records · Page 3Linked to original sources

On sgoldstino interpretation of HyperCP events

We discuss possible sgoldstino interpretation of the observation, reported by HyperCP collaboration, of three $Σ^+\to pμ^+μ^-$ decay events with dimuon invariant mass 214.3 MeV within detector resolution. We find that this interpretation is consistent in models with (i) parity conservation in sgoldstino interactions, (ii) pseudoscalar sgoldstino $P$ of mass 214 MeV and heavier scalar sgoldstino, and (iii) low supersymmetry breaking scale, \sqrt{F} = 2.5-60 TeV. In these models, sgoldstino can be observed in decays $K^+\toπ^+π^0 P$, $K_L\toππP$ and $K_S\toππP$ at the branching ratios of at least of order 10^{-12}, 10^{-8} and 10^{-11}, respectively. The model can be probed also at e^+e^- colliders in the channels $e^+e^-\toγP$ and $e^+e^-\to e^+e^-P$, where the cross section is likely to be in the range 1 pb - 5 ab.

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Upper limit on the ultra-high-energy photon flux from AGASA and Yakutsk data

We present the interpretation of the muon and scintillation signals of ultra-high-energy air showers observed by AGASA and Yakutsk extensive air shower array experiments. We consider case-by-case ten highest energy events with known muon content and conclude that at the 95% confidence level (C.L.) none of them was induced by a primary photon. Taking into account statistical fluctuations and differences in the energy estimation of proton and photon primaries, we derive an upper limit of 36% at 95% C.L. on the fraction of primary photons in the cosmic-ray flux above 10^20 eV. This result disfavors the Z-burst and superheavy dark-matter solutions to the GZK-cutoff problem.

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Estimate of the correlation signal between cosmic rays and BL Lacs in future data

The existing correlation between BL Lacertae objects (BL Lacs) and cosmic-ray events observed by HiRes experiment provide sufficient information to formulate quantitatively the hypothesis about the flux of neutral cosmic-ray particles originated from BL Lacs. We determine the potential of future cosmic ray experiments to test this hypothesis by predicting the number of coincidences between arrival directions of cosmic rays and positions of BL Lacs on the celestial sphere, which should be observed in the future datasets. We find that the early Pierre Auger data will not have enough events to address this question. On the contrary, the final Pierre Auger data and the early Telescope Array data will be sufficient to fully test this hypothesis. If confirmed, it would imply the existence of highest-energy neutral particles coming from cosmological distances.

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Ultra-large distance modification of gravity from Lorentz symmetry breaking at the Planck scale

We present an extension of the Randall--Sundrum model in which, due to spontaneous Lorentz symmetry breaking, graviton mixes with bulk vector fields and becomes quasilocalized. The masses of KK modes comprising the four-dimensional graviton are naturally exponentially small. This allows to push the Lorentz breaking scale to as high as a few tenth of the Planck mass. The model does not contain ghosts or tachyons and does not exhibit the van Dam--Veltman--Zakharov discontinuity. The gravitational attraction between static point masses becomes gradually weaker with increasing of separation and gets replaced by repulsion (antigravity) at exponentially large distances.

hep-th↗

Identification of extragalactic sources of the highest energy EGRET photons by correlation analysis

We found significant correlations between the arrival directions of the highest energy photons (E>10 GeV) observed by EGRET and positions of the BL Lac type objects (BL Lacs). The observed correlations imply that not less than three per cent of extragalactic photons at these energies originate from BL Lacs. Some of the correlating BL Lacs have no counterparts in the EGRET source catalog, i.e. do not coincide with strong emitters of gamma-rays at lower energy. The study of correlating BL Lacs suggests that they may form a subset which is statistically different from the total BL Lac catalog; we argue that they are prominent candidates for TeV gamma-ray sources. Our results demonstrate that the analysis of positional correlations is a powerful approach indispensable in cases when low statistics limits or even prohibits the standard case-by-case identification.

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A comparative study of correlations between arrival directions of ultra-high-energy cosmic rays and positions of their potential astrophysical sources

We consider various classes of persistent extragalactic astrophysical sources which have been suggested in literature as possible emitters of ultra-high-energy cosmic rays (UHECR). We compare the strength of the claimed correlations by a uniform procedure for all classes of sources by making use of the AGASA, Yakutsk and HiRes stereo data. BL Lac type objects correlate with the cosmic rays detected by all three independent experiments and are more probably, compared to other astrophysical sources, related to the UHECR origin. With the account of the Galactic magnetic field (not possible for the HiRes data at the moment), apart of BL Lac type objects, unidentified gamma-ray sources may be correlated with AGASA and Yakutsk cosmic rays.

astro-ph↗

Disentangling perturbative and power corrections in precision tau decay analysis

Hadronic tau decay precision data are analyzed with account of both perturbative and power corrections of high orders within QCD. It is found that contributions of high order power corrections are essential for extracting a numerical value for the strange quark mass from the data on Cabibbo suppressed tau decays. We show that with inclusion of new five-loop perturbative corrections in the analysis the convergence of perturbation theory remains acceptable only for few low order moments. We obtain m_s(M_τ) =130\pm 27 MeV in agreement with previous estimates.

hep-ph↗

Testing the correlations between ultra-high-energy cosmic rays and BL Lac type objects with HiRes stereoscopic data

Previously suggested correlations of BL Lac type objects with the arrival directions of the ultra-high-energy cosmic ray primaries are tested by making use of the HiRes stereoscopic data. The results of the study support the conclusion that BL Lacs may be the cosmic ray sources and suggest the presence of a small (a few percent) fraction of neutral primaries at E>10^{19} eV.

astro-ph↗

LHC prospects in searches for neutral scalars in pp\toγγ+jet: SM Higgs boson, radion, sgoldstino

At hadron colliders the $γγ+jet$ channel provides larger signal-to-background ratio in comparison with inclusive $γγ$ channel in hunting for scalars uncharged under the SM gauge group. At NLO in QCD perturbation theory we evaluate selfconsistently the signal significance for the SM Higgs boson production in $γγ+jet$ channel at LHC. Three-body final state kinematics allows for refined cuts. The adjustment of these cuts increases the signal significance upto the level of inclusive channel. Applying a justified simple rescaling procedure to the results obtained for SM Higgs boson, we estimate the LHC prospects in searches for radion and sgoldstino in $γγ+jet$ channel. We have found that this channel is comparable with $γγ$ channel in searches for new physics and deserves further detailed investigations.

hep-ph↗

Declination dependence of the cosmic-ray flux at extreme energies

We study the large-scale distribution of the arrival directions of the highest energy cosmic rays observed by various experiments. Despite clearly insufficient statistics, we find a deficit of cosmic rays at energies higher than 10^{20} eV from a large part of the sky around the celestial North Pole. We speculate on possible explanations of this feature.

astro-ph↗

Narrowing the window for millicharged particles by CMB anisotropy

We calculate the cosmic microwave background (CMB) anisotropy spectrum in models with millicharged particles of electric charge q\sim 10^{-6}-10^{-1} in units of electron charge. We find that a large region of the parameter space for the millicharged particles exists where their effect on the CMB spectrum is similar to the effect of baryons. Using WMAP data on the CMB anisotropy and assuming Big Bang nucleosynthesis value for the baryon abundance we find that only a small fraction of cold dark matter, Omega_{mcp}h_0^2 < 0.007 (at 95% CL), may consists of millicharged particles with the parameters (charge and mass) from this region. This bound significantly narrows the allowed range of the parameters of millicharged particles. In models without paraphoton millicharged particles are now excluded as a dark matter candidate. We also speculate that recent observation of 511 keV gamma-rays from the Galactic bulge may be an indication that a (small) fraction of CDM is comprised of the millicharged particles.

hep-ph↗

Pinning down the kaon form factors in K^+ -> mu^+ nu_mu gamma decay

We find that the normal muon polarization in the decay K->mu nu_mu gamma is very sensitive to the values of the kaon vector F_V and axial-vector F_A form factors. It is shown that the ongoing KEK-E246 experiment can definitely determine the signs of the sum of the form factors if their difference is fixed from other considerations. This method can also verify the form factor values and signs obtained from the K^+ -> l^+ nu_l e^+ e^- decays. A new experiment with sensitivity to the normal and transverse muon polarizations of about 10^-4 will provide a unique possibility to determine the F_V and F_A values with a few percent accuracy.

hep-ph↗

Transverse muon polarization in K+ -> mu+ nu_mu gamma: scanning over the Dalitz plot

We study the potential of the measurement of the transverse muon polarization P_T in the K->mu nu gamma decay with the sensitivity of δP_T ~ 10^{-4}. It is shown that the forthcoming experiment can measure the contribution of the electromagnetic final state interactions to P_T that gives a possibility to unambiguously determine the signs of the sum of the kaon form factors F_V and F_A even without fixing their difference. We also estimate the sensitivity of this experiment to the new physics, which could give rise to T-violation: multi-Higgs doublet models, supersymmetric extensions of the Standard Model, left-right symmetric model and leptoquark models.

hep-ph↗

Long-lived neutralino and ultra-high energy cosmic rays

Secondary photons from decays of metastable neutralinos can contribute to the ultra-high energy cosmic ray flux. The neutralino production rate is too low in acceleration mechanisms to affect the cosmic ray spectrum without emitting enormous energy in photons and neutrinos. However, in top-down models with sources not concentrated in galactic halos, neutralino decays change the spectrum significantly. We estimate the parameters of a model in which photons from neutralino decays are responsible for cosmic ray events with energies above 10^20 eV, and figure out distinctive experimental signatures for this model.

astro-ph↗

Constraints on ultra-high energy neutrinos from optically thick astrophysical accelerators

The Z-burst mechanism invoked to explain ultra-high energy cosmic rays is severely constrained by measurements of the cosmic gamma-ray background by EGRET. We discuss the case of optically thick sources and show that jets and hot spots of active galaxies cannot provide the optical depth required to suppress the photon flux. Other extragalactic accelerators (AGN cores and sites of gamma ray bursts), if they are optically thick, could be tested by future measurements of the secondary neutrino flux.

astro-ph↗

Sgoldstinos: Primaries of Ultra-High Energy Cosmic Rays

I describe supersymmetric extensions of the Standard Model with light sgoldstinos and discuss the explanation of Ultra High Energy Cosmic Rays above GZK cutoff in these models. Also I briefly discuss the possibility to solve other cosmological and astrophysical puzzles, such as gamma-ray bursts and dimming of high-redshift supernovae, within the models with light sgoldstinos.

hep-ph↗

The Beyond the Standard Model Working Group: Summary Report

Report of the "Beyond the Standard Model" working group for the Workshop `Physics at TeV Colliders', Les Houches, France, 21 May - 1 June 2001. It consists of 18 separate parts: 1. Preface; 2. Theoretical Discussion; 3. Numerical Calculation of the mSUGRA and Higgs Spectrum; 4. Theoretical Uncertainties in Sparticle Mass Predictions; 5. High Mass Supersymmetry with High Energy Hadron Colliders; 6. SUSY with Heavy Scalars at LHC; 7. Inclusive Study of MSSM in CMS; 8. Establishing a No-Lose Theorem for NMSSM Higgs Boson Discovery at the LHC; 9. Effects of Supersymmetric Phases on Higgs Production in Association with Squark Pairs in the Minimal Supersymmetric Standard Model; 10. Study of the Lepton Flavour Violating Decays of Charged Fermions in SUSY GUTs; 11. Interactions of the Goldstino Supermultiplet with Standard Model Fields; 12. Attempts at Explaining the NuTeV Observation of Di-Muon Events; 13. Kaluza-Klein States of the Standard Model Gauge Bosons: Constraints From High Energy Experiments; 14. Kaluza-Klein Excitations of Gauge Bosons in the ATLAS Detector; 15. Search for the Randall Sundrum Radion Using the ATLAS Detector; 16. Radion Mixing Effects on the Properties of the Standard Model Higgs Boson; 17. Probing Universal Extra Dimensions at Present and Future Colliders; 18. Black Hole Production at Future Colliders.

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