Volume 62, Issue 3
March 2004, pages 536a-801
pp 536a-536b March 2004
D P Roy Sumanda Banerjee K Sridhar
pp 537-540 March 2004
Supersymmetry at Dø and other new phenomena searches in Run II
The RunII of the Dø experiment was started in March 2001. The first preliminary results on searches for new physics are presented, with a luminosity of ∼ 10 pb^{−1} from the data collected in 2001-2002. We report results in mSUGRA (jets + missingEt channel), GMSB (diphotons), RPV (trileptons and like sign dileptons) and large extra dimensions (dielectrons and diphotons).
pp 541-544 March 2004
Search for supersymmetry at LEP-2
An extensive effort to search for a hint of a supersymmetric signal was carried out by the four LEP Collaborations. All LEP data, up to centre-of-mass energy of 209 GeV, was carefully analysed with no observed SUSY signal. In an attempt to further increase the sensitivity of the search, the four groups combined some of their searches, to no avail.
pp 545-550 March 2004
LEP Higgs boson searches beyond the standard model and minimum supersymmetric standard model
Ever since the center-of-mass energy was increased in 1995 above the Zℴ resonance, the four LEP experiments (ALEPH, DELPHI, OPAL and L3) have renewed their effort to search for the Higgs boson. Data taking ended in the year 2000 with about 130 pb^{−1} of data collected per experiment above 206 GeV ine^{+}e^{−1} collisions but the data analysis is still very active. Most recently, the wealth of theoretical models and predictions has stimulated new analyses and model interpretations which go beyond the standard model and minimal supersymmetric standard model. These include the searches for charged Higgs bosons, models with two Higgs field doublets, searches for ‘fermiophobic’ Higgs decay, invisible Higgs boson decays, decay-mode independent searches, and limits on Yukawa and anomalous Higgs couplings. I review the searches done by the four LEP experiments and present the LEP combined results when they exist.
pp 551-554 March 2004
Searches for physics beyond the standard model inf-f production at LEP II
Preliminary combinations of measurements of the 4 LEP Collaborations of the processe^{+}e^{−}→f-f at LEP II are presented. The combined results are interpreted in terms of contact interactions and the exchange ofZ′ bosons and within models of low-scale gravity in large extra dimensions.
pp 555-560 March 2004
Neutral Higgs bosons in the standard model and in the minimal supersymmetric model: Searches at LEP
During the twelve years of operation of thee^{+}e^{−} collider LEP, the associated collaborations, ALEPH, DELPHI, L3 and OPAL, have extensively searched for Higgs bosons over a broad range of masses. We present the final results from LEP for the standard model Higgs boson which are obtained from a statistical combination of the data from the four experiments. We also present preliminary combined results for neutral Higgs bosons in the minimal supersymmetric model (MSSM) where the Higgs sector is assumed to be CP invariant. Finally, we discuss an alternative MSSM scenario including CP violation in the Higgs sector.
pp 561-563 March 2004
Search for narrow-widtht-t resonances inp-p collisions at √s = 1.8 TeV
We present a preliminary result on a search for narrow-width resonances that decay intot-t pairs using 130 pb^{−1} of lepton + jets data inp-p collisions at √s = 1.8 TeV. No significant deviation is observed from prediction of the standard model, and upper limits at 95% confidence on the product of the production cross-section and its branching fraction tot-t are presented for narrow-width resonances, as a function of resonance massMx. We also use these limits to exclude the existence of a leptophobic top-color particle,X, withM_{x} < 560 GeV/c^{2} and width Γ_{x} = 0.012M_{x}.
pp 565-568 March 2004
Prospects for Higgs search at DØ
The status of the Higgs search at the upgraded DØ detector is discussed.
pp 569-572 March 2004
Progress toward measuring the unitarity angle γ
Measuring the angle γ of the unitarity triangle is an important part of overconstraining the standard model’s explanation of CP violation and testing for new physics contributions to CP violation. Although there are many ways to measure γ, all of them have significant experimental or theoretical challenges. This talk presents progress at the BABAR experiment toward measuring γ usingB meson decays.
pp 573-578 March 2004
Rare kaon decays: K^{+} → π^{+}v-v and future
The experimental progress in the search forK^{+}→ π^{+}v-v will be presented in this paper. Also the physics potential of the proposed BNL experiment to search forK_{L}^{O}→ π^{o}v-v (KOPIO) will be discussed.
pp 579-581 March 2004
NA48 results on neutral kaon and hyperon rare decays
The NA48 Collaboration has performed an extensive program of kaon and hyperon rare decays using the data collected during the period 1997–2001. This program includes new tests of chiral perturbation theory, new measurements of theη mass andK_{s} lifetime and the possibility to measure the Cabibbo angle using Ξ beta decays.
pp 583-586 March 2004
Studies of radiative penguinB decays at BaBar
We summarize results on a number of observations of penguin dominated radiative decays of theB meson. Such decays are forbidden at tree level and proceed via electroweak loops. As such they may be sensitive to physics beyond the standard model. The observations have been made at the BaBar experiment at PEP-II, the asymmetricB factory at SLAC.
pp 587-590 March 2004
Status ofV_{ub} measurement with BELLE detector
Semileptonic decays ofB →X_{u}lv have great importance both from theoretical and experimental point of view, as they are useful for extracting the magnitude ofV_{ub}, one of the tiniest elements of CKM matrix. Similarly measurement ofB √ D_{s}×_{u} can be used to calculateV_{ub} The Belle Collaboration has measured these branching ratios and extractedV_{ub} for various theoretical models.
pp 591-596 March 2004
We present preliminary results of the measurement of branching fractions and CP violating asymmetries inB meson decays toη′K and ØK*. We update also the results of the direct CP violation searches with BABAR in charmless hadronicB meson decays.
pp 597-599 March 2004
Radiative widths of neutral kaon excitations
We observe 147 events of the axial vector pairK_{1}(1270)–K_{1}(1400) produced in the Coulomb field of a Pb target and measure the radiative widths Γ(K_{1}(1400)→K^{0} + γ) = 280.8 ±23.2(stat.) ±40.4(syst.) keV and Γ(K_{1}(1270) →K^{0} + γ) = 73.2 ±6.1(stat.) ±28.3(syst.) keV. These first measurements are lower than the quark-model predictions. We also place upper limits on the radiative widths forK*(1410) andK_{2}^{*} (1430) and find that the latter is very small in accord withSU(3)invariance in the naive quark model.
pp 601-606 March 2004
Direct CP violation in neutral kaon decays
The final result of the NA48 experiment is presented and performed at the CERN SPS neutral kaon beams, on the direct CP violation parameter Re(ε′/ε), as measured from the decay rates of neutral kaons into two pions. The data collected in the years 1997–2001 yield the evidence for the direct CP violation with Re(ε′/ge) = (14.7±2.2) x 10^{−4}. Description of experimental method and systematics, comparison with the corresponding FNAL result and discussion of some implications for the theory are given.
pp 607-610 March 2004
Search of extra space dimensions with ATLAS
If extra spatial dimensions were to exist, they could provide a solution to the hierarchy problem. The studies done by the ATLAS Collaboration on the sensitivity of the detector to various extra dimension models are reported in this document.
pp 611-614 March 2004
Recent discoveries in the neutrino sector have opened a new frontier in highenergy physics and cosmology. Evidence from neutrino oscillation experiments from around the world indicate that neutrinos oscillate between their different flavours and therefore may have mass. In addition, results from solar and atmospheric neutrino experiments as well as the accelerator neutrino experiment, LSND, cannot all be explained with the three standard model neutrinos. Is this new physics or is there some other explanation? The MiniBooNE experiment presently taking data at Fermilab is designed to address the LSND signal and answer this question. Progress on the MiniBooNE experiment will be presented and prospects for the future will be discussed.
pp 615-622 March 2004
Charmonium spectroscopy —A review
A review is presented of the latest developments in the spectroscopy of charmonium.
pp 623-625 March 2004
Fluctuations as a signal of quark-gluon plasma: Present experimental results
pp 627-630 March 2004
Latest results onJ/ψ anomalous suppression
Sérgio Ramos B Alessandro C Alexa R Arnaldi M Atayan C Baglin A Baldit M Bedjidian S Beolè V Boldea P Bordalo S R Borenstein G Borges A Bussière L Capelli C Castanier J Castor B Chaurand B Cheynis E Chiavassa C Cicalo T Claudino M P Comets S Constantinescu P Cortese J Cruz A DeFalco N DeMarco G Dellacasa A Devaux S Dita O Drapier B Espagnon J Fargeix P Force M Gallio Y K Gavrilov C Gerschel P Giubellino M B Golubeva M Gonin A A Grigorian S Grigorian J Y Grossiord F F Guber A Guichard H Gulkanyan R Hakobyan R Haroutunian M Idzik D Jouan T L Karavitcheva L Kluberg A B Kurepin Y Le Bornée C Lourenço P Macciotta M Mac Cormick A Marzari-Chiesa M Masera A Masoni M Monteno A Musso P Petiau A Piccotti J R Pizzi W L Prado da Silva F Prino G Puddu C Quintans L Ramello S Ramos P Rato Mendes L Riccati A Romana H Santos P Saturnini E Scalas E Scomparin S Serci R Shahoyan F Sigaudo M Sitta P Sonderegger X Tarrago N S Topilskaya G L Usai E Vercellin L Villatte N Willis T Wu
The NA50 experiment deals with Pb-Pb collisions at 158 GeV/nucleon at the CERN SPS accelerator. TheJ/ψ production is studied through the muon decay channel, using the Drell-Yan dimuons as a reference. New results based on recent analyses, from data taken with improved experimental conditions and using different centrality estimators, are presented and compared to an update of those already obtained from previous data samples. The stepwise pattern of the anomalousJ/ψ suppression as a function of centrality, already present in these previous results, is confirmed. This observation could be a fingerprint of the theoretically predicted melting of charmonia resonances in a deconfined quark-gluon plasma.
pp 631-633 March 2004
Neutrinoless double beta decay with small and hierarchical neutrino mass
We construct a model where neutrino Majorana masses are small and hierarchical but where neutrinoless double beta decay occurs at an observable rate potentially detectable by present day experiments.
pp 635-638 March 2004
Inconsistencies in interpreting the atmospheric neutrino anomaly
We note a discrepancy between the value ofR expected on the basis of the muon neutrino angular distribution and the value actually observed. The energy independence ofR leads to a fine-tuning problem. This may be indicative of some unaccounted for new physics.
pp 639-642 March 2004
T invariance of Higgs interactions in the standard model
In the standard model, the Cabibbo-Kobayashi-Maskawa matrix, which incorporates the time-reversal violation shown by the charged current weak interactions, originates from the Higgs-quark interactions. The Yukawa interactions of quarks with the physical Higgs particle can contain further complex phase factors, but nevertheless conserveT, as shown by constructing the fermionT transformation and the invariant Euclidean fermion measure.
pp 643-646 March 2004
Bi-large neutrino mixings by radiative magnification
R N Mohapatra M K Parida G Rajasekaran
Starting with the unification hypothesis of mixings of quarks and leptons and small quark-like mixings at the see-saw scale, we find that two large mixings for ν_{e} —νx03BC; andv_{μ}—v_{τ} at the weak scale are obtained as a result of renormalization group evolution and radiative magnification if the three neutrinos are quasi degenerate in masses and possess the same CP parity. We also find thatU_{e3} remains small and well within the CHOOZ-Palo Verde bound since the correspondingV_{ub} for CKM mixing is very small. Several testable pedictions are pointed out.
pp 647-650 March 2004
Radiative stability of neutrino-mass textures
M K Parida C R Das G Rajasekaran
Neutrino-mass textures proposed at high scales are known to be unstable against radiative corrections especially for nearly degenerate mass eigenvalues. We find a mechanism in a class of gauge models including 2HDM where the RG constraints can be evaded. Consequently, a high-scale texture can match the low-energy data or be reproduced at low energies.
pp 651-653 March 2004
Explaining Tevatron leptons photons missing-E_{T} events with supersymmetry
The CDF experiment reported a lepton photon missing transverse energy (ie651_01)signal 3σ in excess of the standard model prediction in Tevatron Run I data. The excess can be explained by the resonant production of a smuon, which subsequently decays to a muon, a photon and a gravitino. Here, we perform combined fits of this model to the CDF (ie651_02) excess, the DO measurement of the same channel and the CDF (ie651_03) channel. Although the rates of the latter two analyses are in agreement with the standard model prediction, our model is in good agreement with these data because their signal to background efficiency is low at the best-fit point. However, they help to constrain the model away from the best fit point.
pp 655-658 March 2004
Required experimental accuracy to select between supersymmetrical models
We will present a method to decidea priori whether various supersymmetrical scenarios can be distinguished based on sparticle mass data alone. For each model, a scan over all free SUSY breaking parameters reveals the extent of that model’s physically allowed region of sparticle-mass-space. Based on the geometrical configuration of these regions in mass-space, it is possible to obtain an estimate of the required accuracy of future sparticle mass measurements to distinguish between the models. We will illustrate this algorithm with an example. This talk is based on work done in collaboration with B C Allanach (LAPTH, Annecy) and F Quevedo (DAMTP, Cambridge).
pp 659-662 March 2004
In supersymmetric models a gluino can decay intotb_{x}^{~}_{1}^{+-} through a stop or a sbottom. The decay chain produces an edge structure in the m_{tb} distribution. Monte Carlo simulation studies show that the end-point and the edge height would be measured at the CERN LHC by using a sideband subtraction technique. The stop and sbottom masses as well as their decay branching ratios are constrained by the measurement. We study interpretations of the measurement.
pp 663-666 March 2004
Constraints on sparticle spectrum in different supersymmetry breaking models
Katri Huitu Jari Laamanen P N Pandita
We derive sum rules for the sparticle masses in different models of supersymmetry breaking. This includes the gravity-mediated models (SUGRA models) as well as models in which supersymmetry breaking terms are induced by super-Weyl anomaly (AMSB models). These sum rules can help in distinguishing between these models. In particular, we obtain an upper bound on the mass of the lightest neutralino as a function of the gluino mass in SUGRA and AMSB models.
pp 667-670 March 2004
Muong — 2 measurements and non-commutative geometry of quantum beams
We discuss a completely quantum mechanical treatment of the measurement of the anomalous magnetic moment of the muon. A beam of muons move in a strong uniform magnetic field and a weak focusing electrostatic field. Errors in the classical beam analysis are exposed. In the Dirac quantum beam analysis, an important role is played by non-commutative muon beam coordinates leading to a discrepancy between the classical and quantum theories. We obtain a quantum limit to the accuracy achievable in BNL type experiments. Some implications of the quantum corrected data analysis for supersymmetry are briefly mentioned.
pp 671-674 March 2004
MSSMcharged Higgs production in the 1 TeV domain and large tanβ determination
pp 675-678 March 2004
On de-globalization in quantum chromodynamics
The recent discovery and resummation of a class of single logarithmic effects (non-global logs), has a significant impact on several QCD observables ranging from the classic Sterman-Weinberg jet definition to currently studied event shapes and rapidity gap observables. The discovery of the above effects overturns, for example, the common wisdom that hadronic energy flow in limited inter-jet regions is dictatedprimarily by the colour flow of the underlying hard partonic subprocess. We discuss some features of non-global logs and the rapid progress being made in estimating and controlling such corrections.
pp 679-682 March 2004
Pseudoscalar-photon mixing and the large scale alignment of QSO optical polarizations
Pankaj Jain Sukanta Panda S Sarala
We review the observation of large scale alignment of QSO optical polarizations. Alignment is seen in patches of distance scale of order 1 Gpc. We argue that the existence of a hypothetical light pseudoscalar can explain these observations.
pp 683-686 March 2004
Higgs production at next-to-next-to-leading order
V Ravindran J Smith W L van Neerven
We describe the calculation of inclusive Higgs boson production at hadronic colliders at next-to-next-to-leading order (NNLO) in perturbative quantum chromodynamics. We have used the technique developed in ref. [4]. Our results agree with those published earlier in the literature.
pp 687-690 March 2004
Possibility of extracting the weak phase 7 from Λ_{b}→ Λ^{0} decays
We explore the possibility of extracting the weak phase γ from pure tree decays Λ_{b}→ Λ(ie687_01) in a model independent way. We find the CP violating phase γ can be determined cleanly without any hadronic uncertainties. Furthermore, these decays are free from the penguin pollution and neither tagging nor time dependent studies are required for the extraction.
pp 691-694 March 2004
Near-horizon states of black holes and Calogero models
B Basu-Mallick Pijush K Ghosh Kumar S Gupta
We find self-adjoint extensions of the rational Calogero model in the presence of the harmonic interaction. The corresponding eigenfunctions may describe the near-horizon quantum states of certain types of black holes.
pp 695-698 March 2004
Alok Kumar Rashmi R Nayak Sanjay
We show the existence of classical solutions ofD-branes as well as a system ofD3-branes oriented at an arbitrary angle with respect to each other, in a six-dimensionalpp-wave background obtained fromAdS_{3} × S^{3} ×R^{4}, withR — R andNS — NS 3-from flux. The world volume coordinate of D5-brane lies along the six-dimensional pp-wave directions, whereas thepp-wave direction is transverse to the system of D3-branes. We also present moreD-brane bound state solutions by applyingT-duality symmetries. The system ofD3-branes oriented at an arbitrary angle is shown to preserve 1/16 supersymmetries. Finally a brief discussion of the open string construction is presented for both the cases.
pp 699-702 March 2004
Logarithmic corrections to entropy and AdS/CFT
We calculate the correction to the Bekenstein-Hawking entropy formula for five-dimensional AdS-Schwarzschild black holes due to thermodynamic fluctuations. The result is then compared with the boundary gauge theory entropy corrections via AdS/CFT correspondence.
pp 703-706 March 2004
Intersectingp — p′ branes inpp-wave background
Anindya Biswas Alok Kumar Kamal L Panigrahi
Several supergravity solutions corresponding to bothDp, as well asDp—Dp′ systems, inNS-NS andR-R pp-wave background originating fromAdS_{3} xS^{3} xR^{4} are presented. The supersymmetry properties of these solutions are analysed along with a brief outline of the world sheet construction for thep — p′ branes.
pp 707-710 March 2004
A Kerr metric describing a rotating black hole is obtained on the three brane in a five-dimensional Randall-Sundrum brane world by considering a rotating five-dimensional black string in the bulk. We examine the causal structure of this space-time through the geodesic equations.
pp 711-715 March 2004
Orientifolds of type IIA strings on Calabi-Yau manifolds
Suresh Govindarajan Jaydeep Majumder
We identify type IIA orientifolds that are dual toM-theory compactifications on manifolds withG_{2}-holonomy. We then discuss the construction of cross-cap states in Gepner models.
pp 717-720 March 2004
The gravity dual of the non-perturbativeN = 2 supersymmetric Yang-Mills theory
The anomalous Ward identity is derived forN = 2 SUSY Yang-Mills theories, which is resulted out of wrapping ofD_{5} branes on supersymmetric two cycles. Prom the ward identity one obtains the Witten-Dijkgraaf-Verlinde-Verlinde equation and hence can solve for the pre-potential. This way one avoids the problem of enhancon which maligns the non-perturbative behaviour of the Yang-Mills theory resulted out of wrapped branes.
pp 721-724 March 2004
N = 1 super quantum chromo dynamics and fractional branes
In this talk we show how to get the one-loop beta function and the chiral anomaly ofN = 1 super QCD from a stack of fractionalND3-branes localized inside the world-volume of 2M fractionalD7-branes in the orbifoldC^{3}/(Z_{2} ×Z_{2}). They are obtained by analyzing the classical supergravity background generated by such a brane configuration, in the spirit of the gauge/gravity correspondence.
pp 725-727 March 2004
Cancellation of global anomalies in spontaneously broken gauge theories
I discuss the generalization to global gauge anomalies of the familiar procedure for the cancellation of local gauge anomalies in effective theories of spontaneously broken symmetries
pp 729-731 March 2004
Gauge coupling renormalization in AdS_{5}
We present the relation of the 4-dimensional low energy gauge coupling and the 5-dimensional fundamental gauge coupling of bulk gauge boson in a slice of AdS_{5}, which is orbifolded byZ_{2} ×Z′_{2}. We calculate the full 1-loop corrections for the case of generic 5-dimensional scalar, Dirac fermion, and vector fields with arbitraryZ_{2}×Z′_{2}. For the supersymmetric case, we obtain the result more easily by using the 4-dimensional effective supergravity approach.
pp 733-736 March 2004
Realistic split fermion models
The standard model flavor structure can be explained in theories where the fermions are localized on different points in a compact extra dimension. We explain how models with two bulk scalars compactified on an orbifold can produce such separations in a natural way. We show that, generically, models of Gaussian overlaps are unnatural since they require very large Yukawa couplings between the fermions and the bulk scalars. We present a two-scalar model that accounts naturally for the quark flavor parameters and in particular yields order one CP violating phase.
pp 737-739 March 2004
Primordial braneworld black holes: Significant enhancement of lifetimes through accretion
The Randall-Sundrum (RS-II) braneworld cosmological model with a fraction of the total energy density in primordial black holes is considered. Due to their 5d geometry, these black holes undergo modified Hawking evaporation. It is shown that during the high-energy regime, accretion from the surrounding radiation bath is dominant compared to evaporation. This effect increases the mass of the black holes till the onset of matter (or black hole) domination of the total energy density. Thus black holes with even very small initial masses could survive till several cosmologically interesting eras.
pp 741-743 March 2004
A five-dimensional model of varying fine structure constant
The cosmological variation of the fine structure constant α is explored from an effective theory, under the form of an improved version of the 5D Kaluza-Klein theory.
pp 745-748 March 2004
Scalar field dynamics on a brane
The dynamics of a flat isotropic brane Universe with two-component matter source —perfect fluid with the equation of statep = (γ − 1)ρ and a scalar field with a power-law potentialV ∼ φ^{α} is investigated. We describe solutions for which the scalar field energy density scales as a power-law of the scale factor. We also describe solutions existing in regions of the parameter space where these scaling solutions are unstable or do not exist.
pp 749-752 March 2004
Mimicking trans-Planckian effects in the CMB with conventional physics
We investigate the possibility that fields coupled to the inflaton can influence the primordial spectrum of density perturbations through their coherent motion. For example, the second field in hybrid inflation might be oscillating at the beginning of inflation rather than at the minimum of its potential. Although this effect is washed out if inflation lasts long enough, we note that there can be up to 30e-foldings of inflation prior to horizon crossing of COBE fluctuations while still giving a potentially visible distortion. Such pumping of the inflaton fluctuations by purely conventional physics can resemble trans-Planckian effects which have been widely discussed. The distortions which they make to the CMB could leave a distinctive signature which differs from generic effects like tilting of the spectrum.
pp 753-756 March 2004
Recently there have been important developments in the determination of neutron star masses which put severe constraints on the composition and equation of state (EOS) of the neutron star matter. Here we study the effect of quark and nuclear matter mixed phase on mass radius relationship of neutron stars employing recent models from two classes of EOS’s and discuss their implications.
pp 757-760 March 2004
We study cosmological effects of homogeneous tachyon field as dark energy. We concentrate on two different scalar field potentials, the inverse square potential and the exponential potential. These models have a unique feature that the matter density parameter and the density parameter for tachyons remain comparable for a large range in red-shift. It is shown that there exists a range of parameters for which the universe undergoes an accelerated expansion and the evolution is consistent with structure formation requirements. For a viable model we require fine tuning of parameters comparable to that in ACDM or in quintessence models. For the exponential potential, the accelerated phase is followed by a phase witha(t)αt^{2/3} thus eliminating a future horizon.
pp 761-764 March 2004
Baryogenesis via density fluctuations with a second-order electroweak phase transition
Biswanath Layer Soma Sanyal Ajit M Srivastava
We consider the presence of cosmic string-induced density fluctuations in the early universe at temperatures below the electroweak phase transition temperature. Resulting temperature fluctuations can restore the electroweak symmetry locally, depending on the amplitude of fluctuations and the background temperature. The symmetry will be spontaneously broken again in a given region as the temperature drops there (for fluctuations with length scales smaller than the horizon), resulting in the production of baryon asymmetry. The time-scale of the transition will be governed by the wavelength of fluctuation and, hence, can be much smaller than the Hubble time. This leads to strong enhancement in the production of baryon asymmetry for a second-order electroweak phase transition as compared to the case when transition happens due to the cooling of the universe via expansion. For a two-Higgs doublet model (with appropriate CP violation), we show that one can get the required baryon asymmetry if fluctuations propagate without getting significantly damped. If fluctuations are damped rapidly, then a volume factor suppresses the baryon production, though it is still 3–4 orders of magnitude larger than the conventional case of second-order transition.
pp 765-770 March 2004
Cosmology with rolling tachyon
M Sami Pravabati Chingangbam Tabish Qureshi
We examine the possibility of rolling tachyon to play the dual role of inflaton at early epochs and dark matter at late times. We argue that enough inflation can be generated with the rolling tachyon either by invoking the large number of branes or brane world assisted inflation. However, reheating is problematic in this model.
pp 771-773 March 2004
Leptogenesis with left-right domain walls
U A Yajnik J Cline M Rabikumar
The presence of domain walls separating regions of unbrokenSU(2)_{L} andSU(2)_{R} is shown to provide necessary conditions for leptogenesis which converts later to the observed baryon asymmetry. The strength of lepton number violation is related to the Majorana neutrino mass and hence related to current bounds on light neutrino masses. Thus the observed neutrino masses and the baryon asymmetry can be used to constrain the scale of left-right symmetry breaking.
pp 775-778 March 2004
Neutrino—antineutrino asymmetry around rotating black holes
Banibrata Mukhopadhyay Parampreet Singh
Propagation of fermion in curved space-time generates gravitational interaction due to the coupling between spin of the fermion and space-time curvature. This gravitational interaction appears as a CPT violating term in the Lagrangian. It is seen that this space-time interaction can generate neutrino asymmetry in the Universe. If the background metric is spherically asymmetric, say, of a rotating black hole, this interaction is non-zero, thus the net difference to the number density of the neutrino and anti-neutrino is non-zero.
pp 779-783 March 2004
Late time phase transition as dark energy
We show that the dark energy field can naturally be described by the scalar condensates of a non-abelian gauge group. This gauge group is unified with the standard model gauge groups and it has a late time phase transition. The small phase transition explains why the positive acceleration of the universe is occurring only recently. The model hasno free parameters but for the matter content of the group. The initial energy density at the unification scale and at the condensation scale are fixed by the number of degrees of freedom of the gauge group.
pp 785-787 March 2004
Neutrino—nucleon cross-section at ultra-high energies in models with large extra dimensions
We examine whether the models with large extra dimensions can provide an explanation for the GZK violating ultra-high energy cosmic rays (UHECR). In these models the neutrino—nucleon cross-section rises rapidly with energy and hence cosmic rays might be identified with neutrinos. We calculate the neutrino-nucleon cross-section at ultra high energies by assuming that it is dominated by the production ofp-branes. We perform the calculation in a generalized Randall-Sundrum model and Lykken-Randall model and find cross-sections of the order of 100 mb at neutrino energies of 10^{20} eV, which is required for explaining UHECR events.
pp 789-792 March 2004
Ultra-high energy cosmic rays and prompt TeV gamma rays from gamma ray bursts
Pijushpani Bhattacharjee Nayantara Gupta
Gamma ray bursts (GRBs) have been proposed as one possible class of sources of the ultrahigh energy cosmic ray (UHECR) events observed up to energies ≳ 10^{20} eV. The synchrotron radiation of the highest energy protons accelerated within the GRB source should produce gamma rays up to TeV energies. Here we briefly discuss the implications on the energetics of the GRB from the point of view of the detectability of the prompt TeV γ-rays of proton-synchrotron origin in GRBs in the up-coming ICECUBE muon detector in the south pole.
pp 793-796 March 2004
Statistical isotropy of the cosmic microwave background
The breakdown of statistical homogeneity and isotropy of cosmic perturbations is a generic feature of ultra-large scale structure of the cosmos, in particular, of non-trivial cosmic topology. The statistical isotropy (SI) of the cosmic microwave background temperature fluctuations (CMB anisotropy) is sensitive to this breakdown on the largest scales comparable to, and even beyond the cosmic horizon. We propose a set of measures,K_{l} (l = 1, 2,3,...) which for non-zero values indicate and quantify statistical isotropy violations in a CMB map. We numerically compute the predictedK_{l} spectra for CMB anisotropy in flat torus universe models. Characteristic signatures of different models in theK_{l} spectrum are noted.
pp 797-801 March 2004
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