Wed·Jan 20, 2016Wednesday·January 20, 2016

1. 01*

   The Diphoton Excess Inspired Electroweak Baryogenesis

   Wei Chao🇺🇸

   A resonance in the diphoton channel with invariant mass $m_{\gamma \gamma }=750$ GeV was claimed by the ATLAS and CMS collaborations at the run-2 LHC with $\sqrt{s}=13$ TeV. In this paper, we explain this diphoton excess as a pseudo-scalar singlet, which is produced at the LHC through gluon fusion with exotic scalar quarks running in the loop. We point out the scalar singlet might trigger a two-step electroweak phase transition, which can be strongly first oder. By assuming there are CP violations associated with interactions of the scalar quarks, the model is found to be able to generate adequate baryon asymmetry of the Universe through the electroweak baryogenesis mechanism. Constraints on the model are studied.

   hep-ph43 citations
2. 02*

   Relic density of wino-like dark matter in the MSSM

   M. Beneke🇩🇪 · A. Bharucha🇫🇷 · F. Dighera🇩🇪 · C. Hellmann🇩🇪 · A. Hryczuk🇳🇴 · S. Recksiegel🇩🇪 · P. Ruiz-Femenia🇩🇪

   The relic density of TeV-scale wino-like neutralino dark matter in the MSSM is subject to potentially large corrections as a result of the Sommerfeld effect. A recently developed framework enables us to calculate the Sommerfeld-enhanced relic density in general MSSM scenarios, properly treating mixed states and multiple co-annihilating channels as well as including off-diagonal contributions. Using this framework, including on-shell one-loop mass splittings and running couplings and taking into account the latest experimental constraints, we perform a thorough study of the regions of parameter space surrounding the well known pure-wino scenario: namely the effect of sfermion masses being non-decoupled and of allowing non-negligible Higgsino or bino components in the lightest neutralino. We further perform an investigation into the effect of thermal corrections and show that these can safely be neglected. The results reveal a number of phenomenologically interesting but so far unexplored regions where the Sommerfeld effect is sizeable. We find, in particular, that the relic density can agree with experiment for dominantly wino neutralino dark matter with masses ranging from 1.7 to beyond 4 TeV. In light of these results the bounds from Indirect Detection on wino-like dark matter should be revisited.

   hep-phastro-ph.HEJHEP(2016)·96 citations
3. 03*

   Wide or Narrow? The Phenomenology of 750 GeV Diphotons

   Matthew R. Buckley🇺🇸

   I perform a combined analysis of the ATLAS and CMS diphoton data, using both Run-I and Run-II results, including those released at the 2016 Moriond conference. I find combining the ATLAS and CMS results from Run-II increases the statistical significance of the reported 750 GeV anomaly, assuming a spin-0 mediator coupling to gluons or heavy quarks with a width much smaller than the detector resolution. This significance does not decrease when the 8 TeV data is included. A spin-2 mediator is disfavored compared to the spin-0 case. The cross section required to fit the ATLAS anomaly is in tension with the aggregate data, all of which prefers a smaller value. The best fit for all models I consider is a $4.0\sigma$ local significance for a 750 GeV spin-0 mediator coupling to gluons with a cross section of 4 fb at 13 TeV (assuming narrow width) or 10~fb (assuming $\Gamma =45$ GeV).

   hep-phEPJC(2016)·60 citations
4. 04*

   Mass Limit for Light Flavon with Residual $Z_3$ Symmetry

   Yu Muramatsu🇰🇷 · Takaaki Nomura🇰🇷 · Yusuke Shimizu🇰🇷

   We present a modified Altarelli and Feruglio $A_4$ model where an additional $A_4$ singlet-prime flavon is introduced. In this model, non-zero ${\theta }_{13}$ is given by this additional $A_4$ singlet-prime flavon which breaks tri-bimaximal mixing. In the framework of the supersymmetry with $U(1{)}_R$ symmetry, we obtain vacuum expectation values (VEVs) and VEV alignments of flavons through driving fields. It is considered that flavon induces distinctive flavor violating process if flavon mass is light. Assuming mass of SUSY particles are sufficiently heavy so that the SUSY contributions can be negligible, we discuss the flavor violating Yukawa interaction through flavon exchange in the charged lepton sector. According to the potential analysis, the VEV of flavon breaks $A_4$ down to $Z_3$ in the charged lepton sector and relation among flavon masses is determined. Thanks for the residual $Z_3$ symmetry, many lepton flavor violating decay modes are forbidden except for $\tau \to \mu \mu \bar{e}$ and $\tau \to ee\bar{\mu }$. A mass limit of the flavon from these three-body decay modes is $60$~GeV taking into account the current experimental lower bounds at the Belle experiment. In our model, we predict a ratio of the branching ratios $\tau \to \mu \mu \bar{e}$ and $\tau \to ee\bar{\mu }$ by using known charged lepton masses. We also find that the production cross section for the flavon can be $\mathcal{O}(1)$ fb. Thus the flavon would be found at the LHC run 2 by searching for 4-tau lepton signal.

   hep-phhep-exJHEP(2016)·17 citations
5. 05*

   Flavor changing nucleon decay

   Nobuhiro Maekawa🇯🇵 · Yu Muramatsu🇰🇷

   Recent discovery of neutrino large mixings implies the large mixings in the diagonalizing matrices of $\bar{5}$ fields in $SU(5)$ grand unified theory (GUT), while the diagonalizing matrices of $10$ fields of $SU(5)$ are expected to have small mixings like Cabibbo-Kobayashi-Maskawa matrix. We calculate the predictions of flavor changing nucleon decays (FCND) in $SU(5)$, $SO(10)$, and $E_6$ GUT models which have the above features for mixings. We found that FCND can be the main decay mode especially for GUT with higher rank unification group. Recent report for $P\to {\pi }^0{\mu }^{+}$ process implies $E_6$ or $SO(10)$ GUT if the signal is from the nucleon decay.

   hep-phPLB(2017)·10 citations
6. 06*

   Dynamical net-proton fluctuations near a QCD critical point

   Christoph Herold🇹🇭 · Marlene Nahrgang🇺🇸 · Yupeng Yan🇹🇭 · Chinorat Kobdaj🇹🇭

   We investigate the evolution of the net-proton kurtosis and the kurtosis of the chiral order parameter near the critical point in the model of nonequilibrium chiral fluid dynamics. The order parameter is propagated explicitly and coupled to an expanding fluid of quarks and gluons in order to describe the dynamical situation in a heavy-ion collision. We study the critical region near the critical point on the crossover side. There are two sources of fluctuations: non-critical initial event-by-event fluctuations and critical fluctuations. These fluctuations can be distinguished by comparing a mean-field evolution of averaged thermodynamic quantities with the inclusion of fluctuations at the phase transition. We find that while the initial state fluctuations give rise to flat deviations from statistical fluctuations, critical fluctuations reveal a clear structure of the phase transition. The signals of the critical point in the net-proton and sigma field kurtosis are affected by the nonequilibrium dynamics and the inhomogeneity of the space-time evolution but develop clearly.

   hep-phPRC(2016)·81 citations
7. 07*

   Dilepton production rate in a hot and magnetized quark-gluon plasma

   N. Sadooghi🇮🇷 · F. Taghinavaz🇮🇷

   The differential multiplicity of dileptons in a hot and magnetized quark-gluon plasma, ${\Delta }_B\equiv d{N}_B/d^{4}x{d}^{4}q$, is derived from first principles. The constant magnetic field $B$ is assumed to be aligned in a fixed spatial direction. It is shown that the anisotropy induced by the $B$ field is mainly reflected in the general structure of photon spectral density function. This is related to the imaginary part of the vacuum polarization tensor, $\text{mbox}Im[{\Pi }^{\mu \nu }]$, which is derived in a first order perturbative approximation. As expected, the final analytical expression for ${\Delta }_B$ includes a trace over the product of a photonic part, $\text{mbox}Im[{\Pi }^{\mu \nu }]$, and a leptonic part, ${\mathcal{L}}_{\mu \nu }$. It is shown that ${\Delta }_B$ consists of two parts, ${\Delta }_B^{\Vert }$ and ${\Delta }_B^{\perp }$, arising from the components $(\mu ,\nu )=(\Vert ,\Vert )$ and $(\mu ,\nu )=(\perp ,\perp )$ of $\text{mbox}Im[{\Pi }^{\mu \nu }]$ and ${\mathcal{L}}_{\mu \nu }$. Here, the transverse and longitudinal directions are defined with respect to the direction of the $B$ field. Combining ${\Delta }_B^{\Vert }$ and ${\Delta }_B^{\perp }$, a novel anisotropy factor ${\nu }_B$ is introduced. Using the final analytical expression of ${\Delta }_B$, the possible interplay between the temperature $T$ and the magnetic field strength $eB$ on the ratio ${\Delta }_B/{\Delta }_0$ and ${\nu }_B$ is numerically studied. Here, ${\Delta }_0$ is the Born approximated dilepton multiplicity in the absence of external magnetic fields. It is, in particular, shown that for each fixed $T$ and $B$, in the vicinity of certain threshold energies, ${\Delta }_B\gg {\Delta }_0$ and ${\Delta }_B^{\perp }\gg {\Delta }_B^{\Vert }$. The latter anisotropy may be interpreted as one of the microscopic sources of the macroscopic anisotropies, reflecting themselves, e.g., in the elliptic asymmetry factor $v_2$ of dileptons.

   hep-phnucl-thAnnals Phys.(2017)·65 citations
8. 08*

   Quark and pion effective couplings from polarization effects

   Fabio L. Braghin🇧🇷

   A flavor SU(2) effective model for pions and quarks is derived by considering polarization effects departing from the usual quark-quark effective interaction induced by dressed gluon exchange, i.e. a global color model for QCD. For that, the quark field is decomposed into a component that yields light mesons and the quark-antiquark condensate, being integrated out by means of the auxiliary field method, and another component which yields constituent quarks, which is basically a background quark field. Within a longwavelength and weak quark field expansion (or large quark effective mass expansion) of a quark determinant, the leading terms are found up to the second order in a zero order derivative expansion, by neglecting vector mesons that are considerably heavier than the pion. Pions are considered in the structureless limit and, besides the chiral invariant terms that reproduce previously derived expressions, symmetry breaking terms are also presented. The leading chiral quark-quark effective couplings are also found corresponding to a NJL and a vector-NJL couplings. All the resulting effective coupling constants and parameters are expressed in terms of the current and constituent quark masses and of the coupling $g$.

   hep-phhep-thnucl-thEPJA(2016)·19 citations
9. 09*

   NNLO phenomenology using N-jettiness subtraction

   Radja Boughezal🇺🇸

   We discuss next-to-next-to-leading order QCD results for Higgs, W-boson and Z-boson production in association with a jet in hadronic collisions, obtained using the recently developed N-jettiness subtraction method.

   hep-phPoS(2016)·1 citation
10. 10*

    An extension of two-Higgs-doublet model and the excesses of 750 GeV diphoton, muon g-2 and $h\to \mu \tau$

    Xiao-Fang Han🇨🇳 · Lei Wang🇨🇳 · Jin Min Yang🇨🇳

    In this paper we simultaneously explain the excesses of the 750 GeV diphoton, muon g-2 and $h\to \mu \tau$ in an extension of the two-Higgs-doublet model (2HDM) with additional vector-like fermions and a CP-odd scalar singlet ($P$) which is identified as the 750 GeV resonance. This 750 GeV resonance has a mixing with the CP-odd scalar ($A$) in 2HDM, which leads to a coupling between $P$ and the SM particles as well as a coupling between $A$ and the vector-like fermions. Such a mixing and couplings are strongly constrained by $\tau \to \mu \gamma$, muon g-2 and the 750 GeV diphoton data. We scan over the parameter space and find that such an extension can simultaneously account for the observed excesses of 750 GeV diphoton, muon g-2 and $h\to \mu \tau$. The 750 GeV resonance decays in exotic modes, such as $P\to hA$, $P\to HZ$, $P\to HA$ and $P\to W^{\pm }{H}^{\mp }$, and its width can be dozens of GeV and is sensitive to the mixing angle.

    hep-phPLB(2016)·68 citations
11. 11*

    The calorimetric spectrum of the electron-capture decay of ${}^{163}$Ho. The spectral endpoint region

    A. De Rújula🇪🇸 · M. Lusignoli🇮🇹

    The electron-neutrino mass (or masses and mixing angles) may be directly measurable in weak electron-capture decays. The favoured experimental technique is "calorimetric". The optimal nuclide is ${}^{163}$Ho, and several experiments (ECHo, HOLMES and NuMECS) are currently studying its decay. The most relevant range of the calorimetric-energy spectrum extends for the last few hundred eV below its endpoint. It has not yet been well measured. We explore the theory, mainly in the cited range, of electron capture in ${}^{163}$Ho decay. A so far neglected process turns out to be most relevant: electron-capture accompanied by the shake-off of a second electron. Our two main conclusions are very encouraging: the counting rate close to the endpoint may be more than an order of magnitude larger than previously expected; the "pile-up" problem may be significantly reduced.

    hep-phnucl-thphysics.atom-phJHEP(2016)·25 citations
12. 12*

    Mass generation and the problem of seagull divergences

    C. T. Figueiredo🇧🇷 · A. C. Aguilar🇧🇷

    The gluon mass generation is a purely non-perturbative effect, and the natural framework to study it in the continuum are the Schwinger-Dyson equations (SDEs) of the theory. At the level of the SDEs the generation of such a mass is associated with the existence of infrared finite solutions for the gluon propagator. From the theoretical point of view, the dynamical gluon mass generation has been traditionally plagued with seagull divergences. In this work, we will review how such divergences can be eliminated completely by virtue of a characteristic identity, valid in dimensional regularization. As a pedagogical example, we will first discuss in the context of scalar QED how it is possible to eliminate all seagull divergences, by triggering the aforementioned special identity, which enforces the masslessness of the photon. Then, we will discuss what happens in QCD and present an Ansatz for the three gluon vertex, which completely eliminates all seagull divergences and at same time allows for the possibility of a dynamical gluon mass generation.

    hep-phJ.Phys.Conf.Ser.(2016)·2 citations
13. 13*

    Stability of superfluid vortices in dense quark matter

    Mark G. Alford (1) · S. Kumar Mallavarapu (1) · Tanmay Vachaspati (2) · Andreas Windisch (1) ((1) Physics Department, Washington University, St. Louis, (2) Physics Department, Arizona State University)

    Superfluid vortices in the color-flavor-locked (CFL) phase of dense quark matter are known to be energetically disfavored relative to well-separated triplets of "semi-superfluid" color flux tubes. However, the short-range interaction (metastable versus unstable) has not been established. In this paper we perform numerical calculations using the effective theory of the condensate field, mapping the regions in the parameter space of coupling constants where the vortices are metastable versus unstable. For the case of zero gauge coupling we analytically identify a candidate for the unstable mode, and show that it agrees well with the results of the numerical calculations. We find that in the region of the parameter space that seems likely to correspond to real-world CFL quark matter the vortices are unstable, indicating that if such matter exists in neutron star cores it is very likely to contain semi-superfluid color flux tubes rather than superfluid vortices.

    ↳ nucl-thastro-ph.SRhep-phPRC(2016)·30 citations
14. 14*

    Observable Properties of Quark-Hadron Phase Transition at the Large Hadron Collider

    Rudolph C. Hwa🇺🇸 · C. B. Yang🇨🇳

    Quark-hadron phase transition is simulated by an event generator that incorporates the dynamical properties of contraction due to QCD confinement forces and randomization due to the thermal behavior of a large quark system on the edge of hadronization. Fluctuations of emitted pions in the $(\eta ,\varphi )$ space are analyzed using normalized factorial moments in a wide range of bin sizes. The scaling index $\nu$ is found to be very close to the predicted value in the Ginzburg-Landau formalism. The erraticity indices ${\mu }_q$ are determined in a number of ways that lead to the same consistent values. They are compared to the values from the Ising model, showing significant difference in a transparent plot. Experimental determination of $\nu$ and ${\mu }_q$ at the LHC are now needed to check the reality of the theoretical study and to provide guidance for improving the model description of quark-hadron phase transition.

    ↳ nucl-thhep-phnucl-exActa Phys.Polon.B(2017)·17 citations
15. 15*

    Simulated Milky Way analogues: implications for dark matter direct searches

    Nassim Bozorgnia🇳🇱 · Francesca Calore🇳🇱 · Matthieu Schaller🇬🇧 · Mark Lovell🇳🇱 · Gianfranco Bertone🇳🇱 · Carlos S. Frenk🇬🇧 · Robert A. Crain🇬🇧 · Julio F. Navarro🇨🇦 · Joop Schaye🇳🇱 · Tom Theuns🇬🇧

    We study the implications of galaxy formation on dark matter direct detection using high resolution hydrodynamic simulations of Milky Way-like galaxies simulated within the EAGLE and APOSTLE projects. We identify Milky Way analogues that satisfy observational constraints on the Milky Way rotation curve and total stellar mass. We then extract the dark matter density and velocity distribution in the Solar neighbourhood for this set of Milky Way analogues, and use them to analyse the results of current direct detection experiments. For most Milky Way analogues, the event rates in direct detection experiments obtained from the best fit Maxwellian distribution (with peak speed of 223 - 289 km/s) are similar to those obtained directly from the simulations. As a consequence, the allowed regions and exclusion limits set by direct detection experiments in the dark matter mass and spin-independent cross section plane shift by a few GeV compared to the Standard Halo Model, at low dark matter masses. For each dark matter mass, the halo-to-halo variation of the local dark matter density results in an overall shift of the allowed regions and exclusion limits for the cross section. However, the compatibility of the possible hints for a dark matter signal from DAMA and CDMS-Si and null results from LUX and SuperCDMS is not improved.

    ↳ astro-ph.COastro-ph.GAhep-phJCAP(2016)·135 citations
16. 16*

    NEUTRINOS: Mysterious Particles with Fascinating Features, which led to the Physics Nobel Prize 2015

    Alexis Aguilar-Arevalo🇲🇽 · Wolfgang Bietenholz🇲🇽

    The most abundant particles in the Universe are photons and neutrinos. Both types of particles are whirling around everywhere, since the early Universe. Hence the neutrinos are all around us, and permanently pass through our planet and our bodies, but we do not notice: they are extremely elusive. They were suggested as a theoretical hypothesis in 1930, and discovered experimentally in 1956. Ever since their properties keep on surprising us; for instance, they are key players in the violation of parity symmetry. In the Standard Model of particle physics they appear in three types, known as "flavors", and since 1998/9 we know that they keep on transmuting among these flavors. This "neutrino oscillation" implies that they are massive, contrary to the previous picture, with far-reaching consequences. This discovery was awarded the Physics Nobel Prize 2015.

    ↳ physics.pop-phhep-phphysics.hist-phRev.Cub.Fis.(2015)·4 citations
17. 17*

    Axionic dark matter signatures in various halo models

    J. D. Vergados (KAIST University)🇰🇷 · Y. Semertzidis (KAIST University)🇰🇷

    In the present work we study possible time signatures Axion Dark Matter searches employing resonant cavities for various halo models. We study in particular the time dependence of the resonance width (modulation) and possible asymmetries in directional experiments.

    ↳ astro-ph.GAhep-phNPB(2017)·15 citations
18. 18*

    Inflationary universe in fluid description

    Kazuharu Bamba🇯🇵

    We investigate a fluid description of inflationary cosmology. It is shown that the three observables of the inflationary universe: the spectral index of the curvature perturbations, the tensor-to-scalar ratio of the density perturbations, and the running of the spectral index, can be compatible with the Planck analysis. In addition, we reconstruct the equation of state (EoS) for a fluid from the spectral index of the curvature perturbations consistent with the Planck results. We explicitly demonstrate that the universe can gracefully exit from inflation in the reconstructed fluid models. Furthermore, we explore the singular inflation for a fluid model.

    ↳ gr-qcastro-ph.COhep-phhep-th1 citation
19. 19*

    The Effective Field Theorist's Approach to Gravitational Dynamics

    Rafael A. Porto🇧🇷

    We review the effective field theory (EFT) approach to gravitational dynamics. We focus on extended objects in long-wavelength backgrounds and gravitational wave emission from spinning binary systems. We conclude with an introduction to EFT methods for the study of cosmological large scale structures.

    ↳ hep-thastro-ph.COgr-qchep-phPhys.Rept.(2016)·555 citations
20. 20*

    Catalysis of Dynamical Chiral Symmetry Breaking by Chiral Chemical Potential

    V. V. Braguta🇷🇺 · A. Yu. Kotov🇷🇺

    In this paper we study the properties of media with chiral imbalance parameterized by chiral chemical potential. It is shown that depending on the strength of interaction between constituents in the media the chiral chemical potential either creates or enhances dynamical chiral symmetry breaking. Thus the chiral chemical potential plays a role of the catalyst of dynamical chiral symmetry breaking. Physically this effect results from the appearance of the Fermi surface and additional fermion states on this surface which take part in dynamical chiral symmetry breaking. An interesting conclusion which can be drawn is that at sufficiently small temperature chiral plasma is unstable with respect to condensation of Cooper pairs and dynamical chiral symmetry breaking even for vanishingly small interactions between constituents.

    ↳ hep-thhep-phPRD(2016)·72 citations
21. 21*

    EPFL Lectures on Conformal Field Theory in D>= 3 Dimensions

    Slava Rychkov🇨🇭

    This is a writeup of lectures given at the EPFL Lausanne in the fall of 2012. The topics covered: physical foundations of conformal symmetry, conformal kinematics, radial quantization and the OPE, and a very basic introduction to conformal bootstrap.

    ↳ hep-thcond-mat.stat-mechhep-ph393 citations
22. 22*

    The worldline approach to helicity flip in plane waves

    Anton Ilderton🇸🇪 · Greger Torgrimsson🇸🇪

    We apply worldline methods to the study of vacuum polarisation effects in plane wave backgrounds, in both scalar and spinor QED. We calculate helicity-flip probabilities to one loop order and treated exactly in the background field, and provide a toolkit of methods for use in investigations of higher-order processes. We also discuss the connections between the worldline, S-matrix, and lightfront approaches to vacuum polarisation effects.

    ↳ hep-thhep-phPRD(2016)·22 citations
23. 23*

    Highlights from the COMPASS experiment at CERN -- Hadron spectroscopy and excitations

    Frank Nerling (COMPASS collaboration)🇩🇪

    The COMPASS experiment at the CERN-SPS studies the spectrum and the structure of hadrons by scattering high energy hadrons and polarised muons off various fixed targets. Recent results for the hadron programme comprise highlights from different topics. A selective overview is given and, among others, the following results are discussed. The precise determination of the pion polarisability, a long standing puzzle that has been solved now, is presented as well as measurements of radiative widths. The observation of a new narrow axial-vector state, the $a_1(1420)$, as well as deeper insights into the exotic $1^{-+}$-wave, which is under study since decades by several experiments, are discussed and further, the search for the charmonium-like exotic $Z_c(3900)$ state in the COMPASS data is covered.

    ↳ hep-exhep-phEPJ Web Conf.(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.