Thu·Mar 31, 2016Thursday·March 31, 2016

1. 01*

   Light-front representation of chiral dynamics with Delta isobar and large-N_c relations

   C. Granados🇺🇸 · C. Weiss🇺🇸

   Transverse densities describe the spatial distribution of electromagnetic current in the nucleon at fixed light-front time. At peripheral distances b = O(M_pi^{-1}) the densities are governed by chiral dynamics and can be calculated model-independently using chiral effective field theory (EFT). Recent work has shown that the EFT results can be represented in first-quantized form, as overlap integrals of chiral light-front wave functions describing the transition of the nucleon to soft-pion-nucleon intermediate states, resulting in a quantum-mechanical picture of the peripheral transverse densities. We now extend this representation to include intermediate states with Delta isobars and implement relations based on the large-N_c limit of QCD. We derive the wave function overlap formulas for the Delta contributions to the peripheral transverse densities by way of a three-dimensional reduction of relativistic chiral EFT expressions. Our procedure effectively maintains rotational invariance and avoids the ambiguities with higher-spin particles in the light-front time-ordered approach. We study the interplay of pi-N and pi-Delta intermediate states in the quantum-mechanical picture of the densities in a transversely polarized nucleon. We show that the correct N_c-scaling of the charge and magnetization densities emerges as the result of the particular combination of currents generated by intermediate states with degenerate N and Delta. The off-shell behavior of the chiral EFT is summarized in contact terms and can be studied easily. The methods developed here can be applied to other peripheral densities and to moments of the nucleon's generalized parton distributions.

   hep-phnucl-thJHEP(2016)·14 citations
2. 02*

   A Critical Appraisal and Evaluation of Modern PDFs

   A. Accardi🇺🇸 · S. Alekhin🇩🇪 · J. Blümlein🇩🇪 · M.V. Garzelli🇩🇪 · K. Lipka🇩🇪 · W. Melnitchouk🇺🇸 · S. Moch🇩🇪 · R. Placakyte🇩🇪 · J.F. Owens🇺🇸 · E. Reya🇩🇪 · N. Sato🇺🇸 · A. Vogt🇬🇧 · O. Zenaiev🇩🇪

   We review the present status of the determination of parton distribution functions (PDFs) in the light of the precision requirements for the LHC in Run 2 and other future hadron colliders. We provide brief reviews of all currently available PDF sets and use them to compute cross sections for a number of benchmark processes, including Higgs boson production in gluon-gluon fusion at the LHC. We show that the differences in the predictions obtained with the various PDFs are due to particular theory assumptions made in the fits of those PDFs. We discuss PDF uncertainties in the kinematic region covered by the LHC and on averaging procedures for PDFs, such as advocated by the PDF4LHC15 sets, and provide recommendations for the usage of PDF sets for theory predictions at the LHC.

   hep-phhep-exEPJC(2016)·191 citations
3. 03*

   Pinning down electroweak dipole operators of the top quark

   Markus Schulze🇨🇭 · Yotam Soreq🇺🇸

   We consider hadronic top quark pair production and pair production in association with a photon or a $Z$ boson to probe electroweak dipole couplings in $t\bar{b}W$, $t\bar{t}\gamma$ and $t\bar{t}Z$ interactions. We demonstrate how measurements of these processes at the 13 TeV LHC can be combined to disentangle and constrain anomalous dipole operators. The construction of cross section ratios allows us to significantly reduce various uncertainties and exploit orthogonal sensitivity between the $t\bar{t}\gamma$ and $t\bar{t}Z$ couplings. In addition, we show that angular correlations in $t\bar{t}$ production can be used to constrain the remaining $t\bar{b}W$ dipole operator. Our approach yields excellent sensitivity to the anomalous couplings and can be a further step towards precise and direct measurements of the top quark electroweak interactions.

   hep-phEPJC(2016)·104 citations
4. 04*

   A 750 GeV graviton from holographic composite dark sectors

   Adrian Carmona🇨🇭

   We show that the 750 GeV di-photon excess can be interpreted as a spin-2 resonance arising from a strongly interacting dark sector featuring some departure from conformality. This spin-2 resonance has negligible couplings to the SM particles, with the exception of the SM gauge bosons which mediate between the two sectors. We have explicitly studied the collider constraints as well as some theoretical bounds in a holographic five dimensional model with a warp factor that deviates from AdS${}_5$. In particular, we have shown that it is not possible to decouple the vector resonances arising from the strong sector while explaining the di-photon anomaly and keeping the five dimensional gravity theory under perturbative control. However, vector resonances with masses around the TeV scale can be present while all experimental constraints are met.

   hep-phhep-exPLB(2016)·24 citations
5. 05*

   Inclusive Dark Photon Search at LHCb

   Philip Ilten🇺🇸 · Yotam Soreq🇺🇸 · Jesse Thaler🇺🇸 · Mike Williams🇺🇸 · Wei Xue🇺🇸

   We propose an inclusive search for dark photons $A^{\prime }$ at the LHCb experiment based on both prompt and displaced di-muon resonances. Because the couplings of the dark photon are inherited from the photon via kinetic mixing, the dark photon $A^{\prime }\to {\mu }^{+}{\mu }^{-}$ rate can be directly inferred from the off-shell photon ${\gamma }^{\ast }\to {\mu }^{+}{\mu }^{-}$ rate, making this a fully data-driven search. For Run 3 of the LHC, we estimate that LHCb will have sensitivity to large regions of the unexplored dark-photon parameter space, especially in the 210-520 MeV and 10-40 GeV mass ranges. This search leverages the excellent invariant-mass and vertex resolution of LHCb, along with its unique particle-identification and real-time data-analysis capabilities.

   hep-phhep-exPRL(2016)·218 citations
6. 06*

   Three-jet production in electron-positron collisions using the CoLoRFulNNLO method

   Vittorio Del Duca🇨🇭 · Claude Duhr🇨🇭 · Adam Kardos🇭🇺 · Gábor Somogyi🇭🇺 · Zoltán Trócsányi🇭🇺

   We introduce a subtraction method for jet cross sections at next-to-next-to-leading order (NNLO) accuracy in the strong coupling and use it to compute event shapes in three-jet production in electron-positron collisions. We validate our method on two event shapes, thrust and C-parameter, which are already known in the literature at NNLO accuracy and compute for the first time oblateness and the energy-energy correlation at the same accuracy.

   hep-phPRL(2016)·183 citations
7. 07*

   Flavor-changing decays of the top quark in 5D warped models

   Alfonso Diaz-Furlong🇲🇽 · Mariana Frank🇨🇦 · Nima Pourtolami🇨🇦 · Manuel Toharia🇨🇦 · Reyna Xoxocotzi🇲🇽

   We study flavor changing neutral current decays of the top quark in the context of general warped extra dimensions, where the five dimensional metric is slightly modified from 5D anti-de-Sitter (AdS${}_5$). These models address the Planck-electroweak hierarchies of the Standard Model $and$ can obey all the low energy flavor bounds and electroweak precision tests, while allowing the scale of new physics to be at the TeV level, and thus within the reach of the LHC at Run II. We perform the calculation of these exotic top decay rates for the case of a bulk Higgs, and thus include in particular the effect of the additional Kaluza-Klein (KK) Higgs modes running in the loops, along with the usual KK fermions and KK gluons.

   hep-phPRD(2016)·10 citations
8. 08*

   Diphotons from an Electroweak Triplet-Singlet

   Kiel Howe🇺🇸 · Simon Knapen🇺🇸 · Dean J. Robinson🇺🇸

   The neutral component of a real pseudoscalar electroweak (EW) triplet can produce a diphoton excess at 750 GeV, if it is somewhat mixed with an EW singlet pseudoscalar. This triplet-singlet mixing allows for greater freedom in the diboson branching ratios than the singlet-only case, but it is still possible to probe the parameter space extensively with 300 fb${}^{-1}$. The charged component of the triplet is pair-produced at the LHC, which results in a striking signal in the form of a pair of $W\gamma$ resonances with an irreducible rate of 0.27 fb. Other signatures include multiboson final states from cascade decays of the triplet-singlet neutral states. A large class of composite models feature both EW singlet and triplet pseudo-Nambu Goldstone bosons in their spectrum, with the diboson couplings generated by axial anomalies.

   hep-phPRD(2016)·16 citations
9. 09*

   Color Instabilities in the Quark-Gluon Plasma

   Stanislaw Mrowczynski🇵🇱 · Bjoern Schenke🇺🇸 · Michael Strickland🇺🇸

   When the quark-gluon plasma (QGP) - a system of deconfined quarks and gluons - is in a nonequilibrium state, it is usually unstable with respect to color collective modes. The instabilities, which are expected to strongly influence dynamics of the QGP produced in relativistic heavy-ion collisions, are extensively discussed under the assumption that the plasma is weakly coupled. We begin by presenting the theoretical approaches to study the QGP, which include: field theory methods based on the Keldysh-Schwinger formalism, classical and kinetic theories, and fluid techniques. The dispersion equations, which give the spectrum of plasma collective excitations, are analyzed in detail. Particular attention is paid to a momentum distribution of plasma constituents which is obtained by deforming an isotropic momentum distribution. Mechanisms of chromoelectric and chromomagnetic instabilities are explained in terms of elementary physics. The Nyquist analysis, which allows one to determine the number of solutions of a dispersion equation without explicitly solving it, and stability criteria are also discussed. We then review various numerical approaches - purely classical or quantum - to simulate the temporal evolution of an unstable quark-gluon plasma. The dynamical role of instabilities in the processes of plasma equilibration is analyzed.

   hep-phhep-thnucl-thPhys.Rept.(2017)·90 citations
10. 10*

    Evaluation of reactor neutrino flux: issues and uncertainties

    Petr Vogel🇺🇸

    Evaluation of the reactor ${\bar{\nu }}_e$ flux and spectrum is an essential ingredient of their application in the neutrino oscillation studies. Two anomalies, i.e. discrepancies between the observed and expected count rates, are widely discussed at the resent time. The total rate is $\sim$ 6\% lower than the expectation at all distances $>$ 10 m from the reactor. And there is a shoulder (often referred to as "bump") at neutrino energies 5-7 MeV, not predicted in the calculated spectrum. I review the ways the flux and spectrum is evaluated and concentrate on the error budget. I argue that far reaching conclusions based on these anomalies should await a thorough understanding of the uncertainties of the spectrum, and point out possible standard physics sources of the anomalies.

    hep-phnucl-th8 citations
11. 11*

    Determination of mass hierarchy with ${\nu }_{\mu }\to {\nu }_{\tau }$ appearance and the effect of nonstandard interactions

    Ahmed Rashed🇪🇬 · Alakabha Datta🇺🇸

    Crucial developments in neutrino physics would be the determination of the mass hierarchy (MH) and measurement of the CP phase in the leptonic sector. The patterns of the transition probabilities $P({\nu }_{\mu }\to {\nu }_{\tau })$ and $P({\bar{\nu }}_{\mu }\to {\bar{\nu }}_{\tau })$ are sensitive to these oscillation parameters. An asymmetry parameter can be defined as the difference of these two probabilities normalized to their sum. The profile of the asymmetry parameter gives a clear signal of the mass ordering as it is found to be positive for inverted hierarchy and negative for normal hierarchy. The asymmetry parameter is also sensitive to the CP phase. We consider the effects of non-standard neutrino interactions (NSI) on the determination of the mass hierarchy. Since we assume the largest new physics effects involve the $\tau$ sector only, we ignore NSI in production and study the NSI effects in detection as well as along propagation. We find that the NSI effects can significantly modify the prediction of the asymmetry parameter though the MH can still be resolved.

    hep-phhep-exInt.J.Mod.Phys.A(2017)·11 citations
12. 12*

    Centrality dependence of midrapidity density from GeV to TeV heavy-ion collisions in the effective-energy universality picture of hadroproduction

    Edward K.G. Sarkisyan🇨🇭 · Aditya Nath Mishra🇮🇳 · Raghunath Sahoo🇮🇳 · Alexander S. Sakharov🇨🇭

    The dependence on centrality, or on the number of nucleon participants, of the midrapidity density of charged particles measured in heavy-ion collisions at the collision energy of about 20 GeV at RHIC to the highest LHC energy of 5 TeV is investigated within the recently proposed effective-energy approach. This approach relates multihadron production in different types of collisions by combining, under the proper scaling of the collision energy, the constituent quark picture with Landau relativistic hydrodynamics. The measurements are shown to be well described based on the similarity of multihadron production process in (anti)proton-proton interactions and heavy-ion collisions driven by the centrality-dependent effective energy of participants.

    hep-phhep-exnucl-exnucl-thPRD(2016)·50 citations
13. 13*

    About neutral mesons and particle oscillations in the light of field-theoretical prescriptions of Weinberg

    L.M. Slad🇷🇺

    By extending the well-known Weinberg's prescriptions on the diagonalization of the mass term of the Lagrangian without increasing the total number of entities, we get the following conclusions: the set of neutral $K$-mesons consists of two elements, $K_S^0$ and $K_L^0$; the states $K^0$ and ${\bar{K}}^0$ do not exist as physical objects (in the form of particles or "particle mixtures"); the absence of the states $K^0$ and ${\bar{K}}^0$ destroys the grounds for introducing the notion of their oscillations, further replicated as the neutrino oscillation concept. The conclusions concerning the neutral $K$-mesons are also applicable to the neutral $D$-, $B$- and $B_s$-mesons.

    hep-phhep-ex1 citation
14. 14*

    Parton level study of high ET jets in hard QCD processes at LHC

    M. Kaur🇮🇳 · Ruchi Gupta🇮🇳

    Inclusive jet production will dominate the high $Q^2$ final states at the LHC.~In this work we try to estimate the up-to-date expectations, for high $E_T$ jets and their expected origin from the various parton-parton scattering processes. For these studies we have used a standard Parton Distribution Function (PDF) and simulated millions of events with the PYTHIA8 event genertor. The results are compared with simulations for center-of-mass energies of 0.9 TeV, 2.36 TeV, 7 TeV and 14 TeV corresponding to existing and future LHC runs. We present some expectations for the relative cross sections of different quark flavours which indicates that eventually we might be able to measure the cross section for b-flavoured jets with reasonable accuracy up to an $E_T$ of a few TeV.

    hep-ph0 citations
15. 15*

    Electroproduction of tensor mesons in QCD

    V. M. Braun🇩🇪 · N. Kivel🇩🇪 · M. Strohmaier🇩🇪 · A. A. Vladimirov🇩🇪

    Due to multiple possible polarizations hard exclusive production of tensor mesons by virtual photons or in heavy meson decays offers interesting possibilities to study the helicity structure of the underlying short-distance process. Motivated by the first measurement of the transition form factor ${\gamma }^{\ast }\gamma \to f_2(1270)$ at large momentum transfers by the BELLE collaboration we present an improved QCD analysis of this reaction in the framework of collinear factorization including contributions of twist-three quark-antiquark-gluon operators and an estimate of soft end-point corrections using light-cone sum rules. The results appear to be in a very good agreement with the data, in particular the predicted scaling behavior is reproduced in all cases.

    hep-phJHEP(2016)·19 citations
16. 16*

    Testing QCD factorization with phase determinations in $B\to K\pi$,$K\rho$ and $K^{\ast }\pi$ decays

    T. N. Pham🇫🇷

    The success of QCD factorization(QCDF) in predicting branching ratios for charmless $B$ decays to light pseudoscalar and vector mesons and the small CP asymmetries measured at $BABAR$, Belle and LHCb show that the phase in these decays, as predicted by QCDF, are not large. For a precise test of QCDF one needs to extract from the measured decay rates, the phase of the decay amplitude which appears in the interference terms between the tree and penguin contribution. Since the tree amplitude is known at the leading order in ${\Lambda }_{\mathrm{QCD}}/m_b$ and is consistent with the measured tree-dominated decay rates, the QCDF value for the tree amplitude can be used with the measured decay rates to obtain the phases in $B\to K\pi$,$K\rho$, and $K^{\ast }\pi$ decay rates. This is similar to the extraction of the final-state interaction phases in the interference term between $p\bar{p}\to J/\Psi \to e^{+}{e}^{-}$ and $p\bar{p}\to e^{+}{e}^{-}$ and in $J/\Psi \to 0^{-}{0}^{-}$ done previously. In this paper, we present a determination of the phase between the $I=3/2$ tree and $I=1/2$ penguin amplitudes in $B\to K\pi$,$K\rho$ , and $K^{\ast }\pi$ decays using the measured decay rates and the QCDF $I=3/2$ tree amplitude obtained from the $I=2$ B^{+}\to \pi^{+}\pi^{0},\rho^{0}\pi^{+}, \rho^{+}\pi^{0 tree-dominated decays and compare the result with the phase given by QCDF. It is remarkable that the phase extracted from experiments differs only slightly from the QCDF values. This shows that there is no large final-state interaction strong phase in B\to K\pi$,$K\rho$,and$ K^{*}\pi$ decays.

    hep-phhep-exPRD(2016)·3 citations
17. 17*

    Parametric Resonance in Neutrino Oscillation: A Guide to Control the Effects of Inhomogeneous Matter Density

    Masafumi Koike🇯🇵 · Toshihiko Ota🇯🇵 · Masako Saito🇯🇵 · Joe Sato🇯🇵

    Effects of the inhomogeneous matter density on the three-generation neutrino oscillation probability are analyzed. Realistic profile of the matter density is expanded into a Fourier series. Taking in the Fourier modes one by one, we demonstrate that each mode has its corresponding target energy. The high Fourier mode selectively modifies the oscillation probability of the low-energy region. This rule is well described by the parametric resonance between the neutrino oscillation and the matter effect. The Fourier analysis gives a simple guideline to systematically control the uncertainty of the oscillation probability caused by the uncertain density of matter. Precise analysis of the oscillation probability down to the low-energy region requires accurate evaluation of the Fourier coefficients of the matter density up to the corresponding high modes.

    hep-phPLB(2016)·2 citations
18. 18*

    Exotic Hadrons with Heavy Flavors -X, Y, Z and Related States-

    Atsushi Hosaka🇯🇵 · Toru Iijima🇯🇵 · Kenkichi Miyabayashi🇯🇵 · Yoshihide Sakai🇯🇵 · Shigehiro Yasui🇯🇵

    In the past decade, exotic hadrons with charm and bottom flavors have been extensively studied both in experiments and in theories. In this review, we provide topical discussions by selecting $X,Y,Z$ particles, to which Belle has made important contributions. These are $X(3872)$, $Y(4260)$, $Z_c(4430{)}^{+}$, $Z_c(3900{)}^{+}$, $Z_b(10610{)}^{+}$ and $Z_b(10650{)}^{+}$. Based on the current experimental observations, we discuss those states with emphasis on hadronic molecule whose dynamics is governed by chiral symmetry and heavy-quark symmetry of QCD. We also mention briefly various interpretations and some theoretical predictions for the yet undiscovered exotic hadrons.

    hep-phhep-exPTEP(2016)·407 citations
19. 19*

    Can $X(5568)$ be described as a $B_s\pi$, $B\bar{K}$ resonant state?

    Miguel Albaladejo🇪🇸 · Juan Nieves🇪🇸 · Eulogio Oset🇪🇸 · Zhi-Feng Sun🇪🇸 · Xiang Liu🇨🇳

    The D0 Collaboration has recently seen a resonant-like peak in the $B_s\pi$ invariant mass spectrum, claimed to be a new state called $X(5568)$. Using a $B_s\pi$--$B\bar{K}$ coupled channel analysis, implementing unitarity, and with the interaction derived from Heavy Meson Chiral Perturbation Theory, we are able to reproduce the reported spectrum, with a pole that can be associated to the claimed $X(5568)$ state, and with mass and width in agreement with the ones reported in the experimental analysis. However, if the $T$-matrix regularization is performed by means of a momentum cutoff, the value for the latter needed to reproduce the spectrum is $\Lambda =2.80\pm 0.04\text{GeV}$, much larger than a "natural" value $\Lambda \simeq 1\text{GeV}$. In view of this, it is difficult to interpret the nature of this new state. This state would not qualify as a resonance dynamically generated by the unitarity loops. Assuming the observed peak to correspond to a physical state, we make predictions for partners in the $D$, $D^{\ast }$, and $B^{\ast }$ sectors. Their observation (or lack thereof) would shed light into this issue.

    hep-phnucl-thPLB(2016)·56 citations
20. 20*

    Production of extra quarks at the Large Hadron Collider beyond the Narrow Width Approximation

    Stefano Moretti🇬🇧 · Dermot O'Brien🇬🇧 · Luca Panizzi🇬🇧 · Hugo Prager🇬🇧

    This paper explores the effects of both finite width and interference (with background) in the pair production and decay of extra heavy quarks with charge 2/3 at the Large Hadron Collider (LHC). This dynamics is normally ignored in standard experimental searches and we assess herein the regions of validity of current approaches, also evaluating the performances of a set of current experimental analyses at 8 and 13 TeV for the deterimination of the excluded regions in the $(M_{\mathrm{VLQ}},{\Gamma }_{\mathrm{VLQ}})$ plane, $M_{\mathrm{VLQ}}$ being the mass of the VLQ and ${\Gamma }_{\mathrm{VLQ}}$ its width. Further, we discuss the configurations of masses, widths and couplings where the latter breaks down.

    hep-phPRD(2017)·59 citations
21. 21*

    Theoretical Physics Implications of the Binary Black-Hole Mergers GW150914 and GW151226

    Nicolas Yunes🇺🇸 · Kent Yagi🇺🇸 · Frans Pretorius🇺🇸

    The gravitational wave observations GW150914 and GW151226 by Advanced LIGO provide the first opportunity to learn about physics in the extreme gravity environment of coalescing binary black holes. The LIGO Scientific Collaboration and the Virgo Collaboration have verified that this observation is consistent with General Relativity. This paper expands their analysis to a larger class of anomalies, highlighting the inferences that can be drawn on non-standard theoretical physics mechanisms. We find that these events constrain a plethora of mechanisms associated with the generation and propagation of gravitational waves, including the activation of scalar fields, gravitational leakage into large extra dimensions, the variability of Newton's constant, a modified dispersion relation, gravitational Lorentz violation and the strong equivalence principle. Though other observations limit many of these mechanisms already, GW150914 and GW151226 are unique in that they are direct probes of dynamical strong-field gravity and of gravitational wave propagation. We also show that GW150914 constrains inferred properties of exotic compact object alternatives to Kerr black holes. We argue, however, that the true potential for GW150914 to both rule out exotic objects and constrain physics beyond General Relativity is severely limited by the lack of understanding of the merger regime in almost all relevant modified gravity theories. This event thus significantly raises the bar that these theories have to pass, both in terms of having a sound theoretical underpinning, and being able to solve the equations of motion for binary merger events. We conclude with a discussion of the additional inferences that can be drawn if the lower-confidence observation of an electromagnetic counterpart to GW150914 holds true; this would provide dramatic constraints on the speed of gravity and gravitational Lorentz violation.

    ↳ gr-qcastro-ph.HEhep-phhep-thPRD(2016)·791 citations
22. 22*

    Chiral heat wave and mixed waves in kinetic theory

    D. Frenklakh🇷🇺

    We study collective excitations in hot rotating chiral media in presence of magnetic field in kinetic theory, namely Chiral Heat Wave and its' mixings with Chiral Vortical Wave and Chiral Magnetic Wave. Our results for velocities of these waves have slight alterations from those obtained earlier. We explain the origin of these alterations and also give the most general expressions for the velocities of all these waves in hydrodynamic approach.

    ↳ hep-thcond-mat.mes-hallhep-phPRD(2016)·4 citations
23. 23*

    Multiplicity dependent and non-binomial efficiency corrections for particle number cumulants

    Adam Bzdak🇵🇱 · Romain Holzmann🇩🇪 · Volker Koch🇺🇸

    In this note we extend previous work on efficiency corrections for cumulant measurements [1,2]. We will discuss the limitations of the methods presented in these papers. Specifically we will consider multiplicity dependent efficiencies as well as a non-binomial efficiency distributions. We will discuss the most simple and straightforward methods to implement those corrections.

    ↳ nucl-thhep-exhep-phnucl-exPRC(2016)·55 citations
24. 24*

    New Developments in Cosmology

    Stefano Gariazzo🇮🇹

    In this Thesis I discuss several recent results obtained using the CMB spectra measured by Planck and several other cosmological probes. Extensions of the $\Lambda$CDM model are studied, including the presence of an additional sterile neutrino (motivated by the short-baseline oscillation anomalies) and of a thermal axion. The degeneracies of the cosmological effects of these particles with the power spectrum of primordial perturbations are tested. We also show that the power spectrum of initial scalar perturbations can be degenerate with the presence of primordial non-Gaussianities, thus affecting the constraints on the non-Gaussianity parameter $f_{NL}$. Finally, an effective interaction between dark energy and dark matter is studied.

    ↳ astro-ph.COhep-ph0 citations
25. 25*

    The first observations of wide-band interferometers and the spectra of relic gravitons

    Massimo Giovannini🇨🇭

    Stochastic backgrounds of relic gravitons of cosmological origin extend from frequencies of the order of the aHz up to the GHz range. Since the temperature and polarization anisotropies constrain the low frequency normalization of the spectra, in the concordance paradigm the strain amplitude corresponding to the frequency window of wide-band interferometers turns out to be, approximately, nine orders of magnitude smaller than the astounding signal recently reported and attributed to a binary black hole merger. The backgrounds of relic gravitons expected from the early Universe are compared with the stochastic foregrounds stemming from the estimated multiplicity of the astrophysical sources. It is suggested that while the astrophysical foregrounds are likely to dominate between few Hz and 10 kHz, relic gravitons with frequencies exceeding 100 kHz represent a potentially uncontaminated signal for the next generation of high-frequency detectors currently under scrutiny.

    ↳ astro-ph.COgr-qchep-phhep-thPLB(2016)·8 citations
26. 26*

    Equilibrium Instability of Chiral Mesons in External Electromagnetic Field via AdS/CFT

    Seyed Farid Taghavi🇮🇷 · Ali Vahedi🇮🇷

    We study the equilibrium instability of chiral quarkonia in a plasma in the presence of constant magnetic and electric field and at finite axial chemical potential using AdS/CFT duality. The model in use is a supersymmetric QCD at large 'tHooft coupling and number of colors. We show that the presence of the magnetic field and the axial chemical potential even in the absence of the electric field make the system unstable. In a gapped system, a stable/unstable equilibrium state phase transition is observed and the initial transition amplitude of the equilibrium state to the non-equilibrium state is investigated. We demonstrate that at zero temperature and large magnetic field the instability grows linearly by increasing the quarkonium binding energy. In the constant electric and magnetic field, the system is in a equilibrium state if the Ohm's law and the chiral magnetic effect cancel their effects. This happens in a sub-space of $(E,B,T,{\mu }_5)$ space with constraint equation ${\sigma }_{B}B=-\sigma E$, where $\sigma$ and ${\sigma }_B$ are called electric and chiral magnetic conductivity, respectively. We analyze the decay rate of a gapless system when this constraint is slightly violated.

    ↳ hep-thhep-phJHEP(2016)·3 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.