hep-ph updates on
High Energy Physics - Phenomenology (hep-ph) updates on the e-print archive
  • Gauge and gravitational instantons: From 3-forms and fermions to Weak Gravity and flat axion potentials. (arXiv:1906.07728v1 [hep-th])

    Authors: Arthur Hebecker, Philipp Henkenjohann

    We investigate the role of gauge and gravitational instantons in the context of the Swampland program. Our focus is on the global symmetry breaking they induce, especially in the presence of fermions. We first recall and make more precise the description of the dilute instanton gas through a 3-form gauge theory. In this language, the familiar suppression of instanton effects by light fermions can be understood as the decoupling of the 3-form. Even if all fermions remain massive, such decoupling may occur on the basis of an explicitly unbroken but anomalous global symmetry in the fermionic sector. This should be forbidden by quantum gravity, which leads us to conjecture a related, cutoff-dependent lower bound on the induced axion potential. Finally, we note that the gravitational counterpart of the above are K3 instantons. These are small fluctuations of Euclidean spacetime with K3 topology, which induce fermionic operators analogous to the 't Hooft vertex in gauge theories. Although Planck-suppressed, they may be phenomenologically relevant if accompanied by other higher-dimension fermion operators or if the K3 carries appropriate gauge fluxes.

  • Constraining the primordial black hole abundance with 21cm cosmology. (arXiv:1906.07735v1 [astro-ph.CO])

    Authors: Olga Mena, Sergio Palomares-Ruiz, Pablo Villanueva-Domingo, Samuel J. Witte

    The discoveries of a number of binary black hole mergers by LIGO and VIRGO has reinvigorated the interest that primordial black holes (PBHs) of tens of solar masses could contribute non-negligibly to the dark matter energy density. Should even a small population of PBHs with masses $\gtrsim \mathcal{O}(M_\odot)$ exist, they could profoundly impact the properties of the intergalactic medium and provide insight into novel processes at work in the early Universe. We demonstrate here that observations of the 21cm transition in neutral hydrogen during the epochs of reionization and cosmic dawn will likely provide one of the most stringent tests of solar mass PBHs. In the context of 21cm cosmology, PBHs give rise to three distinct observable effects: ${\textit{(i)}}$ the modification to the primordial power spectrum (and thus also the halo mass function) induced by Poisson noise, ${\textit{(ii)}}$ a uniform heating and ionization of the intergalactic medium via X-rays produced during accretion, and ${\textit{(iii)}}$ a local modification to the temperature and density of the ambient medium surrounding isolated PBHs. Using a four-parameter astrophysical model, we show that experiments like SKA and HERA could potentially improve upon existing constraints derived using observations of the cosmic microwave background by more than one order of magnitude.

  • Constraining primordial black hole abundance with the Galactic 511 keV line. (arXiv:1906.07740v1 [astro-ph.CO])

    Authors: William DeRocco, Peter W. Graham

    Models in which dark matter consists entirely of primordial black holes (PBHs) with masses around $10^{17}$ g are currently unconstrained. However, if PBHs are a component of the Galactic dark matter density, they will inject a large flux of energetic particles into the Galaxy as they radiate. Positrons produced by these black holes will subsequently propagate throughout the Galaxy and annihilate, contributing to the Galactic 511 keV line. Using measurements of this line by SPI/INTEGRAL as a constraint on PBH positron injection, we place new limits on PBH abundance in the mass range $10^{16} - 10^{17}$ g, ruling out models in which these PBHs constitute the entirety of dark matter.

  • Naturalness versus stringy naturalness (with implications for collider and dark matter searches. (arXiv:1906.07741v1 [hep-ph])

    Authors: Howard Baer, Vernon Barger, Shadman Salam

    The notion of stringy naturalness-- that an observable O_2 is more natural than O_1 if more (phenomenologically acceptable) vacua solutions lead to

    O_2 rather than O_1-- is examined within the context of the Standard Model (SM) and various SUSY extensions: CMSSM/mSUGRA, high-scale SUSY and radiatively-driven natural SUSY (RNS). Rather general arguments from string theory suggest a (possibly mild) statistical draw towards vacua with large soft SUSY breaking terms. These vacua must be tempered by an anthropic veto of non-standard vacua or vacua with too large a value of the weak scale m(weak). We argue that the SM, the CMSSM and the various high-scale SUSY models are all expected to be relatively rare occurances within the string theory landscape of vacua. In contrast, models with TeV-scale soft terms but with m(weak)~100 GeV and consequent light higgsinos (SUSY with radiatively-driven naturalness) should be much more common on the landscape. These latter models have a statistical preference for m_h~ 125 GeV and strongly interacting sparticles beyond current LHC reach. Thus, while conventional naturalness favors sparticles close to the weak scale, stringy naturalness favors sparticles so heavy that electroweak symmetry is barely broken and one is living dangerously close to vacua with charge-or-color breaking minima, no electroweak breaking or pocket universe weak scale values too far from our measured value. Expectations for how landscape SUSY would manifest itself at collider and dark matter search experiments are then modified compared to usual notions.

  • QCD evolution of the orbital angular momentum of quarks and gluons: Genuine twist-three part. (arXiv:1906.07744v1 [hep-ph])

    Authors: Yoshitaka Hatta, Xiaojun Yao

    We present the numerical solution of the one-loop QCD evolution equation for the genuine twist-three part of the orbital angular momentum (OAM) distributions of quarks and gluons inside a longitudinally polarized nucleon. This is based on the observation that the evolution is identical to that of the Efremov-Teryaev-Qiu-Sterman function for transverse single spin asymmetry. Together with the known evolution of the Wandzura-Wilczek part, the one-loop evolution of OAM distributions is now practically under control. We also study, for the first time, the scale dependence of the potential angular momentum defined as the difference between the Ji and Jaffe-Manohar definitions of OAM.

  • CP Violation in ${\bar B}^0 \to D^{*+} \ell^- {\bar\nu}_\ell$. (arXiv:1906.07752v1 [hep-ph])

    Authors: David London

    At present, there are discrepancies with the predictions of the standard model in ${\bar B}^0 \to D^{*+} \ell^- {\bar\nu}_\ell$ decays, hinting at the presence of new physics (NP) in $b \to c \tau^- {\bar\nu}$. Various NP models have been proposed to explain the data. In this talk, I discuss how the measurement of CP-violating observables in ${\bar B}^0 \to D^{*+} \ell^- {\bar\nu}_\ell$ can be used to differentiate the NP scenarios.

  • Status of isospin splittings in mesons and baryons. (arXiv:1906.07799v1 [hep-ph])

    Authors: Marek Karliner, Jonathan L. Rosner

    Current measurements of isospin splittings in mesons and baryons are sufficiently precise that they allow estimates of the mass difference between constituent up and down quarks. Some previous results are updated in the light of these new measurements, and the importance of better measurements of some observables such as $M(K^{*\pm})$, $M(B^{*0})-M(B^0)$, and isospin splittings in bottom baryons is noted.

  • Flavor changing Flavon decay $\phi\to tc$ ($\phi=H_F,\,A_F$) at the high-luminosity large hadron collider. (arXiv:1906.07821v1 [hep-ph])

    Authors: M. A. Arroyo-Ureña, A. Fernández-Téllez, G. Tavares-Velasco

    We present a study of the flavor changing decays $\phi\to tc$ of the $CP$-even and $CP$-odd scalar Flavons $H_F$ and $A_F$ at the High Luminosity Large Hadron Collider (HL-LHC) in the framework of an extension of the standard model that incorporates an extra complex singlet and invokes the Froggatt-Nielsen mechanism with an Abelian flavor symmetry. A Monte Carlo analysis of the signal and the standard model background is presented for a center-of-mass energy of $\sqrt{s}=14$ TeV and integrated luminosities in the 300-3000 fb$^{-1}$ interval. Constraints on the parameter space of the model from the Higgs boson coupling modifiers $\kappa_i$ are obtained and used to evaluate the Flavon decay widths and the $gg\to\phi\to tc$ production cross section. We analyze the dominant background by considering realistic acceptance cuts, tagging and misstagging efficiencies, etc. It is found that with the current integrated luminosity achieved at the LHC, the $A_F\to tc$ decay is out of the reach of detection. However, in the HL-LHC, such a decay could be at the reach of detection for $m_{A_F}=200-500$ GeV once an integrated luminosity of about 1000 fb$^{-1}$ is achieved. On the other hand, since the branching ratio of the $H_F\to tc$ decay is suppressed by two orders of magnitude as compared to that of the $A_F\to tc$ decay, it seems to be out of the reach of detection even in the HL-LHC.

  • Algorithm to find an all-order in the running coupling solution to an equation of the DGLAP type. (arXiv:1906.07924v1 [hep-ph])

    Authors: Igor Kondrashuk

    We propose an algorithm to find a solution to an integro-differential equation of the DGLAP type for all the orders in the running coupling $\alpha$ with splitting functions given at a fixed order in $\alpha.$ Complex analysis is significantly used in the construction of the algorithm, we found a simpler way to calculate the involved integrals over contours in the complex planes than by any of the methods known at present.

  • Visible narrow cusp structure in $\Lambda_c^+\to p K^- \pi^+$ enhanced by triangle singularity. (arXiv:1906.07942v1 [hep-ph])

    Authors: Xiao-Hai Liu, Gang Li, Ju-Jun Xie, Qiang Zhao

    A resonance-like structure as narrow as 10 MeV is observed in the $K^-p$ invariant mass distributions in $\Lambda_c^+\to p K^- \pi^+$ at Belle. Based on the large data sample of about 1.5 million events and the small bin width of just 1 MeV for the $K^-p$ invariant mass spectrum, the narrow peak is found precisely lying at the $\Lambda\eta$ threshold. While lacking evidence for a quark model state with such a narrow width at this mass region, we find that this narrow structure can be naturally identified as a threshold cusp but enhanced by the nearby triangle singularity via the $\Lambda$-$a_0(980)^+$ or $\eta$-$\Sigma(1660)^+$ rescatterings.

  • On the self-consistency of off-shell Slavnov-Taylor identities in QCD. (arXiv:1906.07996v1 [hep-th])

    Authors: J.A. Gracey, H. Kissler, D. Kreimer

    Using Hopf-algebraic structures as well as diagrammatic techniques for determining the Slavnov-Taylor identities for QCD we construct the relations for the triple and quartic gluon vertices at one loop. By making the longitudinal projection on an external gluon of a Green's function we show that the gluon self-energy of that leg is consistently replaced by a ghost self-energy. The resulting identities are then studied by evaluating all the graphs for an off-shell non-exceptional momentum configuration. In the case of the 3-point function this is for the most general momentum case and for the 4-point function we consider the fully symmetric point.

  • Revisiting instabilities of $S^1/Z_2$ models with loop-induced Fayet-Iliopoulos terms. (arXiv:1906.08002v1 [hep-th])

    Authors: Hiroyuki Abe, Tatsuo Kobayashi, Shohei Uemura, Junji Yamamoto

    We study Fayet-Iliopoulos (FI) terms of 5-dimensional supersymmetric $U(1)$ gauge theory compactified on $S^1/Z_2$. In this model, loop diagrams including matter hypermultiplets and brane chiral multiplets induce FI-terms localized at the fixed points. Localized FI-terms lead instabilities of bulk modes. The form of the induced FI-terms strictly depends on wave function profiles of matter multiplets. It is a non-trivial question whether the vacuum of 1-loop corrected potential is stable under radiative corrections. We investigate this issue and it is found that the stable configuration is obtained when the bulk zero modes shield the brane charge completely.

  • Di-jet/$e^+e^-$+ MET to Probe $Z_2-$Odd Mediators to the Dark Sector. (arXiv:1906.08007v1 [hep-ph])

    Authors: Florian Goertz, Karla Tame-Narvaez, Valentin Tenorth

    We explore a scenario where Dark Matter (DM) couples to the Standard Model mainly via a scalar mediator ${\cal S}$ that is odd under a $Z_2$ symmetry, leading to interesting collider signatures. In fact, if linear interactions with the mediator are absent the most important DM production mechanisms at colliders could lead to final states with missing energy in association with at least two fermions, such as di-jet or di-electron signatures. The framework we consider is model-independent, in a sense that it is only based on symmetry and formulated in the (extended) DM Effective Field Theory (eDMEFT) approach. Moreover, it allows to address the smallness of first-generation fermion masses via suppressed $Z_2$ breaking effects. From a di-jet analysis at the LHC, we find rather loose bounds on the effective ${\cal S}$-${\cal S}$-DM-DM interactions, unless the mediator couples very strongly to SM fermions, while a future $e^+ e^-$ collider, such as CLIC, could deliver tighter constraints on the corresponding model parameters, given the mediator is leptophilic. We finally highlight the parameter space that allows to produce the observed DM density, including constraints from direct-detection experiments.

  • New Physics in $b\to c \tau \nu$: Impact of Polarisation Observables and $B_c\to\tau\nu$. (arXiv:1906.08035v1 [hep-ph])

    Authors: Marta Moscati

    The experimental values of the lepton-flavour-universality tests ${\cal R}(D)$ and ${\cal R}(D^*)$ show a tension of about $3.1\sigma$ with their Standard Model prediction. Motivated by this tension, we perform a fit of the $b\to c\tau\nu$ data. We consider one-particle scenarios imposing consecutive limits on $\text{BR}(B_c\to \tau\nu_\tau)$, and analyse how these limits affect the fits. We include the polarisation observables available to date and predict those that are still to be measured, and conclude that they have a high model-resolving power. For each scenario we also predict ${\cal R}(\Lambda_c)$, observing that an enhancement of ${\cal R}(D^{(*)})$ implies an enhancement of ${\cal R}(\Lambda_c)$ in any scenario. We trace back this enhancement to a sum-rule valid irrespective of the scenario used to fit ${\cal R}(D^{(*)})$.

  • Electroweak corrections to $e^+e^-\to\gamma\gamma$ as a luminosity process at FCC-ee. (arXiv:1906.08056v1 [hep-ph])

    Authors: Carlo M. Carloni Calame, Mauro Chiesa, Guido Montagna, Oreste Nicrosini, Fulvio Piccinini

    We consider large-angle two photon production in $e^+ e^-$ annihilation as a possible process to monitor the luminosity of a future $e^+ e^-$ circular collider (FCC-ee). We review and assess the status of the theoretical accuracy by performing a detailed phenomenological study of next-to-leading order electroweak corrections and leading logarithmic QED contributions due to multiple photon radiation. We also estimate the impact of photonic and fermion-loop corrections at next-to-next-to-leading order and the uncertainty induced by the hadronic contribution to the vacuum polarization. Possible perspectives to address the target theoretical accuracy are briefly discussed.

  • Flux Tube S-matrix Bootstrap. (arXiv:1906.08098v1 [hep-th])

    Authors: Joan Elias Miro, Andrea L. Guerrieri, Aditya Hebbar, Joao Penedones, Pedro Vieira

    We bootstrap the S-matrix of massless particles in unitary, relativistic two dimensional quantum field theories. We find that the low energy expansion of such S-matrices is strongly constrained by the existence of a UV completion. In the context of flux tube physics, this allows us to constrain several terms in the S-matrix low energy expansion or -- equivalently -- on Wilson coefficients of several irrelevant operators showing up in the flux tube effective action. These bounds have direct implications for other physical quantities; for instance, they allow us to further bound the ground state energy as well as the level splitting of degenerate energy levels of large flux tubes. We find that the S-matrices living at the boundary of the allowed space exhibit an intricate pattern of resonances with one sharper resonance whose quantum numbers, mass and width are precisely those of the world-sheet axion proposed in [1,2]. The general method proposed here should be extendable to massless S-matrices in higher dimensions and should lead to new quantitative bounds on irrelevant operators in theories of Goldstones and also in gauge and gravity theories.

  • Weak-field limit of Kaluza-Klein model with non-linear perfect fluid. (arXiv:1906.08214v1 [gr-qc])

    Authors: Ezgi Yalçınkaya, Alexander Zhuk

    In this paper, we investigate the six-dimensional Kaluza-Klein model with spherical compactification of the internal space. Background matter is considered in the form of a perfect fluid with non-linear equations of state both in the external/our and internal spaces and the model is set to include an additional bare cosmological constant $\Lambda_6$. In the weak-field approximation, the background is perturbed by pressureless gravitating mass that is a static point-like particle. The demand that the parameterized post-Newtonian parameter $\gamma$ be equal to 1 in this configuration, first, ensures compatibility with gravitational tests in the Solar system (deflection of light and time delay of radar echoes) at the same level of accuracy as General Relativity. Second, it translates into the absence of internal space variations so that the gravitational potential coincides exactly with the Newtonian one, securing the absence of the fifth force. Third, the gravitating mass remains pressurless in the external space as in the standard approach to non-relativistic astrophysical objects and meanwhile, acquires effective tension in the internal space.

  • Cosmic Conundra Explained by Thermal History and Primordial Black Holes. (arXiv:1906.08217v1 [astro-ph.CO])

    Authors: Bernard Carr, Sebastien Clesse, Juan Garcia-Bellido, Florian Kuhnel

    A universal mechanism may be responsible for several unresolved cosmic conundra. The sudden drop in the pressure of relativistic matter at $W^{\pm} / Z^{0}$ decoupling, the quark-hadron transition and $e^{+}e^{-}$ annihilation enhances the probability of primordial black hole (PBH) formation in the early Universe. Assuming the amplitude of the primordial curvature fluctuations is approximately scale-invariant, this implies a multi-modal PBH mass spectrum with peaks at $10^{-6}$, $1$, $30$, and $10^{6}\,M_{\odot}$. This suggests a unified PBH scenario which naturally explains the dark matter and recent microlensing observations, the LIGO/Virgo black hole mergers, the correlations in the cosmic infrared and X-ray backgrounds, and the origin of the supermassive black holes in galactic nuclei at high redshift. A distinct prediction of our model is that LIGO/Virgo should soon observe the merging of black holes with masses between $2$ and $5\,M_{\odot}$ or above $70\,M_{\odot}$ and with low mass ratios.

  • New constraints on Lorentz Invariance violation from Crab Nebula spectrum beyond $100$ TeV. (arXiv:1906.08221v1 [astro-ph.HE])

    Authors: Petr Satunin

    Recently two collaborations, Tibet and HAWC, presented new measurements of gamma-ray spectrum from Crab Nebula [arXiv:1906.05521, arXiv:1905.12518] which continues beyond $100$ TeV. We use these data to establish two-sided constraints on parameters of Lorentz Invariance violation in quantum electrodynamics. The new constraints are several times stronger than existing in the literature.

  • Migdal Effect in Dark Matter Direct Detection Experiments. (arXiv:1707.07258v3 [hep-ph] UPDATED)

    Authors: Masahiro Ibe, Wakutaka Nakano, Yutaro Shoji, Kazumine Suzuki

    The elastic scattering of an atomic nucleus plays a central role in dark matter direct detection experiments. In those experiments, it is usually assumed that the atomic electrons around the nucleus of the target material immediately follow the motion of the recoil nucleus. In reality, however, it takes some time for the electrons to catch up, which results in ionization and excitation of the atoms. In previous studies, those effects are taken into account by using the so-called Migdal's approach, in which the final state ionization/excitation are treated separately from the nuclear recoil. In this paper, we reformulate the Migdal's approach so that the "atomic recoil" cross section is obtained coherently, where we make transparent the energy-momentum conservation and the probability conservation. We show that the final state ionization/excitation can enhance the detectability of rather light dark matter in the GeV mass range via the {\it nuclear} scattering. We also discuss the coherent neutrino-nucleus scattering, where the same effects are expected.

  • Updated Constraints on Non-Standard Interactions from Global Analysis of Oscillation Data. (arXiv:1805.04530v2 [hep-ph] UPDATED)

    Authors: Ivan Esteban, M.C. Gonzalez-Garcia, Michele Maltoni, Ivan Martinez-Soler, Jordi Salvado

    We quantify our present knowledge of the size and flavor structure of non-standard neutrino interactions which affect the matter background in the evolution of solar, atmospheric, reactor and long-baseline accelerator neutrinos as determined by a global analysis of oscillation data - both alone and in combination with the results on coherent neutrino-nucleus scattering from the COHERENT experiment. We consider general neutral current neutrino interactions with quarks whose lepton-flavor structure is independent of the quark type. We study the dependence of the allowed ranges of non-standard interaction coefficients, the status of the LMA-D solution, and the determination of the oscillation parameters on the relative strength of the non-standard couplings to up and down quarks. Generically we find that the conclusions are robust for a broad spectrum of up-to-down strengths, and we identify and quantify the exceptional cases related to couplings whose effect in neutrino propagation in the Earth or in the Sun is severely suppressed. As a result of the study we provide explicit constraints on the effective couplings which parametrize the non-standard Earth matter potential relevant for long-baseline experiments.

  • Nucleon parton distributions from hadronic quantum fluctuations. (arXiv:1807.06589v3 [hep-ph] UPDATED)

    Authors: Andreas Ekstedt, Hazhar Ghaderi, Gunnar Ingelman, Stefan Leupold

    A physical model is presented for the non-perturbative parton distributions in the nucleon. This is based on quantum fluctuations of the nucleon into baryon-meson pairs convoluted with Gaussian momentum distributions of partons in hadrons. The hadronic fluctuations, here developed in terms of hadronic chiral perturbation theory, occur with high probability and generate sea quarks as well as dynamical effects also for valence quarks and gluons. The resulting parton momentum distributions $f(x,Q_0^2)$ at low momentum transfers are evolved with conventional DGLAP equations from perturbative QCD to larger scales. This provides parton density functions $f(x,Q^2)$ for the gluon and all quark flavors with only five physics-motivated parameters. By tuning these parameters, experimental data on deep inelastic structure functions can be reproduced and interpreted. The contribution to sea quarks from hadronic fluctuations explains the observed asymmetry between $\bar{u}$ and $\bar{d}$ in the proton. The strange-quark sea is strongly suppressed at low $Q^2$, as observed.

  • High Scale Boundary Conditions in Models with Two Higgs Doublets. (arXiv:1810.04518v3 [hep-ph] UPDATED)

    Authors: John McDowall, David J Miller

    We investigate high scale boundary conditions on the quartic Higgs-couplings and their $\beta$-functions in the Type-II Two Higgs Doublet Model and the Inert Doublet Model. These conditions are associated with two possible UV physics scenarios: the Multiple Point Principle, in which the potential exhibits a second minimum at $M_{Pl}$, and Asymptotic Safety, where the scalar couplings run towards an interacting UV fixed point at high scales. We employ renormalisation group running at two-loops and apply theoretical and experimental constraints to their parameter spaces. We find neither model can simultaneously accommodate the MPP whilst also providing realistic masses for both the Higgs and the top quark. However, we do find regions of parameter space compatible with Asymptotic Safety.

  • Fingerprinting the Top quark FCNC via anomalous $Ztq$ couplings at the LHeC. (arXiv:1811.04681v3 [hep-ph] UPDATED)

    Authors: Subhasish Behera, Rashidul Islam, Mukesh Kumar, Poulose Poulose, Rafiqul Rahaman

    A study of the top quark \emph{Flavour Changing Neutral Current} (FCNC) through $Z$-boson has been performed in the proposed future $e^-p$ collider for the energy, $E_{e(p)} = 60~(7000)$~GeV. We considered an effective theory where the anomalous FCNC couplings are of vector and tensor nature. The effect of these couplings is probed in the single top production along with the scattered electron. The polar angle $\theta$ of the electrons coming out of the primary vertex in association with the top quark polarization asymmetries constructed from the angular distribution of the secondary lepton arising from the top decay, allow to distinguish the Lorentz structure of the coupling. From a multi-parameter analysis, we obtain a reach of ${\cal O} (10^{-2})$ in the case of $Ztu$ and $Ztc$ couplings at an integrated luminosity of 2~ab$^{-1}$ at 95\% C.L.

  • Electroweak baryogenesis via bottom transport. (arXiv:1811.08088v3 [hep-ph] UPDATED)

    Authors: Tanmoy Modak, Eibun Senaha

    We consider a scenario in which an extra bottom Yukawa coupling can drive electroweak baryogenesis in the general two-Higgs doublet model. It is found that the new bottom Yukawa coupling with $\mathcal{O}(0.1)$ in magnitude can generate the sufficient baryon asymmetry without conflicting existing data. We point out that future measurements of the bottom Yukawa coupling at High-Luminosity Large Hadron Collider and International Linear Collider, together with the CP asymmetry of $B\to X_s\gamma$ at SuperKEKB provide exquisite probes for this scenario.

  • Finite modular subgroups for fermion mass matrices and baryon/lepton number violation. (arXiv:1812.11072v3 [hep-ph] UPDATED)

    Authors: Tatsuo Kobayashi, Yusuke Shimizu, Kenta Takagi, Morimitsu Tanimoto, Takuya H. Tatsuishi, Hikaru Uchida

    We study a flavor model that the quark sector has the $S_3$ modular symmetry,while the lepton sector has the $A_4$ modular symmetry. Our model leads to characteristic quark mass matrices which are consistent with experimental data of quark masses, mixing angles and the CP violating phase. The lepton sector is also consistent with the experimental data of neutrino oscillations. We also study baryon and lepton number violations in our flavor model.

  • The Isoscalar Mesons and Exotic States in Light Front Holographic QCD. (arXiv:1901.11205v2 [hep-ph] UPDATED)

    Authors: Liping Zou, Hans Günter Dosch, Guy F. de Téramond, Stanley J. Brodsky

    In this article a systematic quantitative analysis of the isoscalar bosonic states is performed in the framework of supersymmetric light front holographic QCD. It is shown that the spectroscopy of the $\eta$ and $h$ mesons can be well described if one additional mass parameter -- which corresponds to the hard breaking of chiral $U(1)$ symmetry in standard QCD -- is introduced. The mass difference of the $\eta$ and $\eta'$ isoscalar mesons is then determined by the strange quark mass content of the $\eta'$. The theory also predicts the existence of isoscalar tetraquarks which are bound states of diquarks and anti-diquarks. The candidates for these exotic isoscalar tetraquarks are identified. In particular, the $f_0(1500)$ is identified as isoscalar tetraquark; the predicted mass value 1.52 GeV agrees with the measured experimental value within the model uncertainties.

  • Multi-Component Dark Matter in a Non-Abelian Dark Sector. (arXiv:1902.04384v2 [hep-ph] UPDATED)

    Authors: Fatemeh Elahi, Sara Khatibi

    In this paper, we explore a dark sector scenario with a gauged $SU(2)_R$ and a global $U(1)_X \times \mathbb{Z}_2$, where the continuous symmetries are spontaneously broken to a global $U(1)_D$. We show that in various regions of the parameter space we can have two, or three dark matter candidates, where these dark matter particles are either a Dirac fermion, a dark gauge boson, or a complex scalar. The phenomenological implications of this scenario are vast and interesting. We identify the parameter space that is still viable after taking into account the constraints from various experiments. We, also, discuss how this scenario can explain the recent observation by DAMPE in the electron-positron spectrum. Furthermore, we comment on the neutrino mass generation through non-renormalizable interactions between the standard model and the dark sector.

  • Extending the constraint for axion-like particles as resonances at the LHC and laser beam experiments. (arXiv:1903.04151v4 [hep-ph] UPDATED)

    Authors: C. Baldenegro, S. Hassani, C. Royon, L. Schoeffel

    We study the discovery potential of axion-like particles (ALP), pseudo-scalars weakly coupled to Standard Model fields, at the Large Hadron Collider (LHC). Our focus is on ALPs coupled to the electromagnetic field, which would induce anomalous scattering of light-by-light. This can be directly probed in central exclusive production of photon pairs in ultra-peripheral collisions at the LHC in proton and heavy ion collisions. We consider non-standard collision modes of the LHC, such as argon-argon collisions at $\sqrt{s_{NN}} = 7$ TeV and proton-lead collisions at $\sqrt{s_{NN}} = 8.16$ TeV to access regions in the parameter space complementary to the ones previously considered for lead-lead or proton-proton collisions. In addition, we show that, using laser beam interactions, we can constrain ALPs as resonant deviations in the refractive index, induced by anomalous light-by-light scattering effects. If we combine the aforementioned approaches, ALPs can be probed in a wide range of masses from the eV scale up to the TeV scale.

  • Fits to Non-Supersymmetric SO(10) Models with Type I and II Seesaw Mechanisms Using Renormalization Group Evolution. (arXiv:1903.08241v2 [hep-ph] UPDATED)

    Authors: Tommy Ohlsson, Marcus Pernow

    We consider numerical fits to non-supersymmetric $\mathrm{SO}(10)$-based models in which neutrino mass is generated by the type-I or type-II seesaw mechanism or a combination of both. The fits are performed with a sophisticated top-down procedure, taking into account the renormalization group equations of the gauge and Yukawa couplings, integrating out relevant degrees of freedom at their corresponding mass scales, and using recent data for the Standard Model observables. We find acceptable fits for normal neutrino mass ordering only and with neutrino mass generated by either type-I seesaw only or a combination of types I and II seesaw in which type-I seesaw is dominant. Furthermore, we find predictions from the best fit regarding the small neutrino masses, the effective neutrinoless double beta decay mass, and the leptonic CP-violating phase. Finally, we show that the fits are rather insensitive to the chosen value of the unification scale.

  • QCD and electroweak corrections to WZ scattering at the LHC. (arXiv:1904.00882v3 [hep-ph] UPDATED)

    Authors: Ansgar Denner, Stefan Dittmaier, Philipp Maierhöfer, Mathieu Pellen, Christopher Schwan

    We present the first computation of the full next-to-leading-order QCD and electroweak corrections to the WZ scattering process at the LHC. All off-shell, gauge-boson-decay, and interference effects are taken into account for the process $\mathrm{p} \mathrm{p} \to \mu^+\mu^-\mathrm{e}^+\nu_\mathrm{e} \mathrm{j} \mathrm{j} + X$ at the orders $\mathcal{O}{\left( \alpha_\mathrm{s} \alpha^6 \right)}$ and $\mathcal{O}{\left( \alpha^7 \right)}$. The electroweak corrections feature the typical Sudakov behaviour towards high energy and amount to $-16\%$ relative to the electroweak contribution to the integrated cross section. Moreover, the corrections induce significant shape distortions in differential distributions. The next-to-leading-order analysis of the quark- and gluon-induced channels is supplemented by a leading-order study of all possible contributions to the full $4\ell+2\mbox{jets}$ production cross section in a realistic fiducial phase-space volume.

  • Pushing the Energy and Cosmic Frontiers with High-Energy Astrophysical Neutrinos. (arXiv:1904.01595v3 [astro-ph.HE] UPDATED)

    Authors: Mauricio Bustamante (Bohr Inst. & Copenhagen U.)

    The astrophysical neutrinos recently discovered by the IceCube neutrino telescope have the highest detected neutrino energies --- from TeV to PeV --- and travel the longest distances --- up to a few Gpc, the size of the observable Universe. These features make them naturally attractive probes of fundamental particle-physics properties, possibly tiny in size, at energy scales unreachable by any other means. The decades before the IceCube discovery saw many proposals of particle-physics studies in this direction. Today, those proposals have become a reality, in spite of prevalent astrophysical unknowns. We showcase examples of studying fundamental neutrino physics at these scales, including some of the most stringent tests of physics beyond the Standard Model.

  • Probing new physics in rare decays of b-flavored Hadrons $b\to s \gamma$ in CMSSM/mSUGRA SUSY SO (10) theories. (arXiv:1904.12566v3 [hep-ph] UPDATED)

    Authors: Gayatri Ghosh

    The implications of the latest measurement of the branching fraction of B($ b\rightarrow s \gamma $) of b hadrons, which is another signature of New Physics beyond Standard Model is presented here. The quark transitions $ b \rightarrow s $, $ b \rightarrow d $ do not happen at tree level in the Standard Model as the Z boson does not couple to quarks of different flavour. In this work the present bounds on the quark transition $ b \rightarrow s $ within the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which there are three independent soft SUSY breaking parameters $ m_{0} $, $ m_{1/2} $ and $ A_{0} $ is illustrated. The recent constraint on B($ b\rightarrow s \gamma $), B($ b_{s}\rightarrow \mu^{+}\mu^{-}$), the recently measured value of Higgs mass at LHC, $ M_{h} $, the value of $\theta_{13}$ from reactor data and the Higgs branching ratios set very strong constraints on New Physics models, in particular supersymmetry. A new epoch for this research has begun since the Large Hadron Collider beauty (LHCb) experiment started affording data for various observables for these decays. The results presented here in mSUGRA/CMSSM models may gain access to supersymmetry even at scales beyond the direct reach of the LHC and the susceptibleness to test these theories at the next run of LHC is also explored.

  • Where Are We With Light Sterile Neutrinos?. (arXiv:1906.00045v2 [hep-ex] UPDATED)

    Authors: A. Diaz, C.A. Argüelles, G.H. Collin, J.M. Conrad, M.H. Shaevitz

    We review the status of searches for sterile neutrinos in the $\sim 1$ eV range, with an emphasis on the latest results from short baseline oscillation experiments and how they fit within sterile neutrino oscillation models. We present global fit results to a three-active-flavor plus one-sterile-flavor model (3+1), where we find an improvement of $\Delta \chi^2=35$ for 3 additional parameters compared to a model with no sterile neutrino. This is a 5$\sigma$ improvement, indicating that an effect that is like that of a sterile neutrino is highly preferred by the data. However we note that separate fits to the appearance and disappearance oscillation data sets within a 3+1 model do not show the expected overlapping allowed regions in parameter space. This "tension" leads us to explore two options: 3+2, where a second additional mass state is introduced, and a 3+1+decay model, where the $\nu_4$ state can decay to invisible particles. The 3+1+decay model, which is also motivated by improving compatibility with cosmological observations, yields the larger improvement, with a $\Delta \chi^2=8$ for 1 additional parameter beyond the 3+1 model, which is a $2.6\sigma$ improvement. Moreover the tension between appearance and disappearance experiments is reduced compared to 3+1, although disagreement remains. In these studies, we use a frequentist approach and also a Bayesean method of finding credible regions.

    With respect to this tension, we review possible problems with the global fitting method. We note multiple issues, including problems with reproducing the experimental results, especially in the case of experiments that do not provide adequate data releases. We discuss an unexpected 5 MeV excess, observed in the reactor flux energy spectrum, that may be affecting the oscillation interpretation of the short baseline reactor data. We emphasize the care that must be taken in mapping to the true neutrino energy in the case of oscillation experiments that are subject to multiple interaction modes and nuclear effects. We point to problems with the "Parameter-Goodness-of-Fit test" that is used to quantify the tension. Lastly, we point out that analyses presenting limits often receive less scrutiny that signals.

    While we provide a snapshot of the status of sterile neutrino searches today and global fits to their interpretation, we emphasize that this is a fast-moving field. We briefly review experiments that are expected to report new data in the immediate future. Lastly, we consider the 5-year horizon, where we propose that decay-at-rest neutrino sources are the best method of finally resolving the confusing situation.

  • Super heavy thermal dark matter. (arXiv:1906.00981v2 [hep-ph] UPDATED)

    Authors: Hyungjin Kim, Eric Kuflik

    We propose a mechanism of elementary thermal dark matter with mass up to $10^{14}$ GeV, within a standard cosmological history, whose relic abundance is determined solely by its interactions with the Standard Model, without violating the perturbative unitarity bound. The dark matter consists of many nearly degenerate particles which scatter with the Standard Model bath in a nearest-neighbor chain, and maintain chemical equilibrium with the Standard Model bath by in-equilibrium decays and inverse decays. The phenomenology includes super heavy elementary dark matter and heavy relics that decay at various epochs in the cosmological history, with implications for CMB, structure formation and cosmic ray experiments.

  • Triplet Leptogenesis, Type-II Seesaw Dominance, Intrinsic Dark Matter, Vacuum Stability and Proton Decay in Minimal SO(10) Breakings. (arXiv:1906.05601v2 [hep-ph] UPDATED)

    Authors: Mainak Chakraborty, M.K. Parida, Biswonath Sahoo (SOA Deemed to be Univ.)

    We implement type-II seesaw dominance for neutrino mass and baryogenesis through heavy scalar triplet leptogenesis in a class of minimal non-supersymmetric SO(10) models where matter parity as stabilising discrete symmetry as well as WIMP dark matter (DM) candidates are intrinsic predictions of the GUT symmetry. We also find modifications of relevant CP-asymmetry formulas in such minimal models. Baryon asymmetry of the universe as solutions of Boltzmann equations is further shown to be realized for both normal and inverted mass orderings in concordance with cosmological bound and best fit values of the neutrino oscillation data including $\theta_{23}$ in the second octant and large values of leptonic Dirac CP-phases. Type-II seesaw dominance is at first successfully implemented in two cases of spontaneous SO(10) breakings through SU(5) route where the presence of only one non-standard Higgs scalar of intermediate mass $\sim 10^9-10^{10}$ GeV achieves unification. Lower values of the SU(5) unification scales $\sim 10^{15}$ GeV are predicted to bring proton lifetimes to the accessible ranges of Super-Kamiokande and Hyper-Kamiokande experiments. Our prediction of WIMP DM relic density in each model is due to a $\sim$ TeV mass matter-parity odd real scalar singlet ($\subset {16}_H \subset$ SO(10)) verifiable by LUX and XENON1T experiments. This DM is also noted to resolve the vacuum stability issue of the standard scalar potential. When applied to the unification framework of M. Frigerio and T. Hambye, in addition to the minimal fermionic triplet DM solution of $2.7$ TeV mass, this procedure of type-II seesaw dominance and triplet leptogenesis is also found to make an alternative prediction of triplet fermion plus real scalar singlet DM at the TeV scale.

  • Improved description of the HERA data with a new simple PDF parametrization. (arXiv:1906.06573v3 [hep-ph] UPDATED)

    Authors: Francesco Giuli, Marco Bonvini

    A new parametrization for the parton distribution functions with a higher flexibility in the small-$x$ region is presented. It has been implemented in the xFitter open-source PDF fitting tool, and compared to the default xFitter parametrization, used for the determination of the HERAPDF set. It has been found that the combined inclusive HERA I+II data can be described using NNLO theory with a significantly higher quality than HERAPDF2.0: the $\chi^2$ is reduced by more than 60 units, having used only four more parameters. Our result highlights a significant parametrization bias in the default xFitter parametrization at small $x$, which would lead to even more dramatic effects when used for higher energy colliders, where the small-$x$ region is more relevant. We also find that the inclusion of small-$x$ resummation leads to a further reduction by approximately 30 extra units in $\chi^2$. In this contribution, we review the results of the recent paper "A new simple PDF parametrization: improved description of the HERA data" (arXiv:1902.11125).

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