Fri·Apr 15, 2016Friday·April 15, 2016

1. 01*

   The Standard Model Higgs as the origin of the hot Big Bang

   Daniel G. Figueroa🇨🇭 · Christian T. Byrnes🇬🇧

   If the Standard Model (SM) Higgs is weakly coupled to the inflationary sector, the Higgs is expected to be universally in the form of a condensate towards the end of inflation. The Higgs decays rapidly after inflation - via non-perturbative effects - into an out-of-equilibrium distribution of SM species, which thermalize soon afterwards. If the post-inflationary equation of state of the universe is stiff, $w\simeq +1$, the SM species eventually dominate the total energy budget. This provides a natural origin for the relativistic thermal plasma of SM species, required for the onset of the `hot Big Bang' era. The viability of this scenario requires the inflationary Hubble scale $H_{\ast }$ to be lower than the instability scale for Higgs vacuum decay, the Higgs not to generate too large curvature perturbations at cosmological scales, and the SM dominance to occur before Big Bang Nucleosynthesis. We show that successful reheating into the SM can only be obtained in the presence of a non-minimal coupling to gravity $\xi \gtrsim 1$, with a reheating temperature of $T_{\mathrm{RH}}\gtrsim \mathcal{O}(10^{10}){\xi }^{3/2}(H_{\ast }/10^{14}\mathrm{GeV}{)}^2\mathrm{GeV}$.

   hep-phastro-ph.COhep-thPLB(2017)·74 citations
2. 02*

   Mono-top Signature from Supersymmetric $t\bar{t}H$ Channel

   Dorival Gonçalves🇬🇧 · Kazuki Sakurai🇬🇧 · Michihisa Takeuchi🇯🇵

   We point out that a distinctive mono-top signature is present in Natural SUSY scenarios when a scalar top-quark and higgsinos are almost mass degenerate. This signature originates from a supersymmetric counter part of the $t\bar{t}H$ process, i.e. $pp\to \tilde{t}t\tilde{h}$. Unlike mono-jet signatures exploiting initial state radiation, this channel can be regarded as a smoking gun signature of a light stop and higgsinos, allowing a direct probe of the stop and neutralino sectors. The production rate of this channel largely depends on the up-type higgsino components in the neutralinos while the stop sector is sensitive to angular distributions of top-quark's decay products. We develop an optimal search strategy to capture the supersymmetric $t\bar{t}H$ process and find that a high luminosity LHC can probe the stop and higgsino sectors with $m_{{\tilde{t}}_1}\lesssim 380$ GeV and $m_{{\tilde{t}}_1}-m_{{\tilde{\chi }}_1^0}\lesssim m_W$. Additionally, we propose a kinematic variable with which one can measure the stop mixing in this channel.

   hep-phhep-exPRD(2016)·12 citations
3. 03*

   Toward a coherent solution of diphoton and flavor anomalies

   Dario Buttazzo🇨🇭 · Admir Greljo🇨🇭 · Gino Isidori🇨🇭 · David Marzocca🇨🇭

   We propose a coherent explanation for the 750 GeV diphoton anomaly and the hints of deviations from Lepton Flavor Universality in B decays in terms a new strongly interacting sector with vectorlike confinement. The diphoton excess arises from the decay of one of the pseudo-Nambu-Goldstone bosons of the new sector, while the flavor anomalies are a manifestation of the exchange of the corresponding vector resonances (with masses in the 1.5-2.5 TeV range). We provide explicit examples (with detailed particle content and group structure) of the new sector, discussing both the low-energy flavor-physics phenomenology and the signatures at high $p_T$. We show that specific models can provide an excellent fit to all available data. A key feature of all realizations is a sizable broad excess in the tails of ${\tau }^{+}{\tau }^{-}$ invariant mass distribution in $pp\to {\tau }^{+}{\tau }^{-}$, that should be accessible at the LHC in the near future.

   hep-phhep-exJHEP(2016)·62 citations
4. 04*

   Black Hole Mergers and the QCD Axion at Advanced LIGO

   Asimina Arvanitaki🇨🇦 · Masha Baryakhtar🇨🇦 · Savas Dimopoulos🇺🇸 · Sergei Dubovsky🇺🇸 · Robert Lasenby🇨🇦

   In the next few years Advanced LIGO (aLIGO) may see gravitational waves (GWs) from thousands of black hole (BH) mergers. This marks the beginning of a new precision tool for physics. Here we show how to search for new physics beyond the standard model using this tool, in particular the QCD axion in the mass range ma ~ 10^-14 to 10^-10 eV. Axions (or any bosons) in this mass range cause rapidly rotating BHs to shed their spin into a large cloud of axions in atomic Bohr orbits around the BH, through the effect of superradiance (SR). This results in a gap in the mass vs. spin distribution of BHs when the BH size is comparable to the axion's Compton wavelength. By measuring the spin and mass of the merging objects observed at LIGO, we could verify the presence and shape of the gap in the BH distribution produced by the axion. The axion cloud can also be discovered through the GWs it radiates via axion annihilations or level transitions. A blind monochromatic GW search may reveal up to 10^5 BHs radiating through axion annihilations, at distinct frequencies within ~3% of $2 ma. Axion transitions probe heavier axions and may be observable in future GW observatories. The merger events are perfect candidates for a targeted GW search. If the final BH has high spin, a SR cloud may grow and emit monochromatic GWs from axion annihilations. We may observe the SR evolution in real time.

   hep-phastro-ph.HEgr-qcPRD(2017)·318 citations
5. 05*

   Realization of Power-Law Inflation & Variants via Variation of the Strong Coupling Constant

   M. AlHallak (Damascus U.) · N. Chamoun (HIAST & Bonn U.)🇸🇾

   We present a model of power law inflation generated by variation of the strong coupling constant. We then extend the model to two varying coupling constants which leads to a potential consisting of a linear combination of exponential terms. Some variants of the latter may be self-consistent and can accommodate the experimental data of the Planck 2015 and other recent experiments.

   hep-phJCAP(2016)·7 citations
6. 06*

   Neutrino mixing and masses in SO(10) GUTs with hidden sector and flavor symmetries

   Xiaoyong Chu🇮🇹 · Alexei Yu. Smirnov🇩🇪

   We consider the neutrino masses and mixing in the framework of SO(10) GUTs with hidden sector consisting of fermionic and bosonic SO(10) singlets and flavor symmetries. The framework allows to disentangle the CKM physics responsible for the CKM mixing and different mass hierarchies of quarks and leptons and the neutrino new physics which produces smallness of neutrino masses and large lepton mixing. The framework leads naturally to the relation $U_{PMNS}\sim V_{CKM}^{†}{U}_0$, where structure of $U_0$ is determined by the flavor symmetry. The key feature of the framework is that apart from the Dirac mass matrices $m_D$, the portal mass matrix $M_D$ and the mass matrix of singlets $M_S$ are also involved in generation of the lepton mixing. This opens up new possibilities to realize the flavor symmetries and explain the data. Using $A_4\times Z_4$ as the flavor group, we systematically explore the flavor structures which can be obtained in this framework depending on field content and symmetry assignments. We formulate additional conditions which lead to $U_0\sim U_{TBM}$ or $U_{BM}$. They include (i) equality (in general, proportionality) of the singlet flavons couplings, (ii) equality of their VEVs; (iii) correlation between VEVs of singlets and triplet, (iv) certain VEV alignment of flavon triplet(s). These features can follow from additional symmetries or be remnants of further unification. Phenomenologically viable schemes with minimal flavon content and minimal number of couplings are constructed.

   hep-phJHEP(2016)·7 citations
7. 07*

   Roles of scalar mesons in charmless ${\Lambda }_b$ decays

   Y.K. Hsiao🇨🇳 · Yu-Heng Lin🇹🇼 · Yao Yu🇨🇳 · C.Q. Geng🇨🇳

   We first study the charmless two-body ${\Lambda }_b$ decays with the scalar mesons as the final states and predict that $\mathcal{B}({\Lambda }_b\to \Lambda f_0(980,1500))=(2.9\pm 0.7,12.4\pm 3.8)\times 10^{-6}$ and $\mathcal{B}({\Lambda }_b\to p{K}_0^{\ast -}(800,1430))=(1.9\pm 0.5,14.1\pm 4.5)\times 10^{-6}$. With the resonant $f_0(980,1500)\to ({\pi }^{+}{\pi }^{-},K^{+}{K}^{-})$ and $K_0^{\ast -}\to {\bar{K}}^0{\pi }^{-}$ decays, we then obtain $\mathcal{B}({\Lambda }_b\to \Lambda ({\pi }^{+}{\pi }^{-},K^{+}{K}^{-}))=(4.2\pm 1.0,3.5\pm 0.7)\times 10^{-6}$ and $\mathcal{B}({\Lambda }_b\to p{\bar{K}}^0{\pi }^{-})=(10.4\pm 2.9)\times 10^{-6}$, in comparison with the data of $(4.6\pm 1.9,15.9\pm 2.6)\times 10^{-6}$ and $(12.6\pm 4.0)\times 10^{-6}$ from LHCb, respectively. Our results for ${\Lambda }_b\to \Lambda {\pi }^{+}{\pi }^{-}$ and ${\Lambda }_b\to p{\bar{K}}^0{\pi }^{-}$ would be regarded as the first evidences of the scalar meson productions in the anti-triplet $b$-baryon decays. The smaller predicted value of $\mathcal{B}({\Lambda }_b\to \Lambda K^{+}{K}^{-})$ indicates the existences of other resonant contributions to the decay, such as ${\Lambda }_b\to K^{-}(N^{\ast +}\to )\Lambda K^{+}$.

   hep-phhep-exPRD(2016)·5 citations
8. 08*

   Production and Decay of Di-photon Resonance at Future $e^{+}{e}^{-}$ Colliders

   Hayato Ito🇯🇵 · Takeo Moroi🇯🇵

   Motivated by the ATLAS and CMS announcements of the excesses of di-photon events, we discuss the production and decay processes of di-photon resonance at future $e^{+}{e}^{-}$ colliders. We assume that the excess of the di-photon events at the LHC is explained by a scalar resonance decaying into a pair of photons. In such a case, the scalar interacts with standard model gauge bosons and, consequently, the production of such a scalar is possible at the $e^{+}{e}^{-}$ colliders. We study the production of the scalar resonance via the associated production with photon or $Z$, as well as via the vector-boson fusion, and calculate the cross sections of these processes. We also study the backgrounds, and discuss the detectability of the signals of scalar production with various decay processes of the scalar resonance. We also consider the case where the scalar resonance has an invisible decay mode, and study how the invisible decay can be observed at the $e^{+}{e}^{-}$ colliders.

   hep-phhep-exPRD(2016)·9 citations
9. 09*

   NLO QCD and electroweak corrections to $ZZ+\mathrm{jet}$ production with $Z$-boson leptonic decays at LHC

   Wang Yong🇨🇳 · Zhang Ren-You🇨🇳 · Ma Wen-Gan🇨🇳 · Li Xiao-Zhou🇨🇳 · Guo Lei🇨🇳

   In this paper we present the full NLO QCD + NLO EW corrections to the $Z$-boson pair production in association with a hard jet at the LHC. The subsequent $Z$-boson leptonic decays are included by adopting both the naive NWA and MadSpin methods for comparison. Since the $ZZ+\mathrm{jet}$ production is an important background for single Higgs boson production and new physics search at hadron colliders, the theoretical predictions with high accuracy for the hadronic production of $ZZ+\mathrm{jet}$ are necessary. We present the numerical results of the integrated cross section and various kinematic distributions of final particles, and conclude that it is necessary to take into account the spin correlation and finite width effects from the $Z$-boson leptonic decays. We also find that the NLO EW correction is quantitatively nonnegligible in matching the experimental accuracy at the LHC, particularly is significant in high transverse momentum region.

   hep-phPRD(2016)·13 citations
10. 10*

    Higgs plus one jet production at NNLO

    Xuan Chen🇨🇳 · Thomas Gehrmann🇨🇭 · Nigel Glover🇬🇧 · Matthieu Jaquier🇩🇪

    We present the computation of Higgs boson plus one jet production at NNLO at the LHC. The computation is carried out in the heavy-top-quark approximation and using the antenna subtraction formalism to handle the IR divergent structure of the individual contributions. All channels and all colours are included. We illustrate aspects of the subtraction formalism and present results for the total cross section as well as distributions in the kinematical variables using a realistic experimental setting. We make a comparison between our results and recent ATLAS data for $H+j$ production.

    hep-phPoS(2016)·16 citations
11. 11*

    Loss of solution in the symmetry improved Phi-derivable expansion scheme

    Gergely Markó🇭🇺 · Urko Reinosa🇫🇷 · Zsolt Szép🇭🇺

    We consider the two-loop Phi-derivable approximation for the O(2)-symmetric scalar model, augmented by the symmetry improvement introduced in [A. Pilaftsis and D. Teresi, Nucl. Phys. B874, 594 (2013)], which enforces Goldstone's theorem in the broken phase. Although the corresponding equations admit a solution in the presence of a large enough infrared (IR) regulating scale, we argue that, for smooth ultraviolet (UV) regulators, the solution is lost when the IR scale becomes small enough. Infrared regular solutions exist for certain non-analytic UV regulators, but we argue that these solutions are artifacts which should disappear when the sensitivity to the UV regulator is removed by a renormalization procedure. The loss of solution is observed both at zero and at finite temperature, although it is simpler to identify in the latter case. We also comment on possible ways to cure this problem.

    hep-phhep-thNPB(2016)·13 citations
12. 12*

    Hints for new sources of flavour violation in meson mixing

    Monika Blanke🇩🇪

    The recent results by the Fermilab Lattice and MILC collaborations on the hadronic matrix elements entering $B_{d,s}-{\bar{B}}_{d,s}$ mixing show a significant tension of the measured values of the mass differences $\Delta M_{d,s}$ with their SM predictions. We review the implications of these results in the context of Constrained Minimal Flavour Violation models. In these models, the CKM elements $\gamma$ and $|V_{ub}|/|V_{cb}|$ can be determined from $B_{d,s}-{\bar{B}}_{d,s}$ mixing observables, yielding a prediction for $\gamma$ below its tree-level value. Determining subsequently $|V_{cb}|$ from the measured value of either $\Delta M_s$ or ${\epsilon }_K$ gives inconsistent results, with the tension being smallest in the Standard Model limit. This tension can be resolved if the flavour universality of new contributions to $\Delta F=2$ observables is broken. We briefly discuss the case of $U(2{)}^3$ flavour models as an illustrative example.

    hep-phNuovo Cim.C(2017)·1 citation
13. 13*

    Discrete Transformation of Baryon- and Lepton-Nonconserving Processes

    Ehsan Jafari🇺🇸

    We consider discrete transformations ($C,P,T$ and $CP$) of baryon- and lepton-nonconserving processes. It has long been thought that values ($\pm 1,\pm i$) form the correct set of fermionic arbitrary phases for discrete transformations. In this paper we show that this idea is not generally true. In order to count the number of fundamental fermions in a process, $F$ number has been introduced. According to our evaluation for any operator which breaks $B-L$ symmetry and violate $F$ number the set of values ($\pm 1,\pm i$) is not the correct set of fermionic arbitrary phases, due to the fact that discrete transformations of such operators will change by altering the fermionic phases from $\pm 1$ to $\pm i$.

    hep-phhep-th0 citations
14. 14*

    Sequestering effects on and of vacuum decay

    Nemanja Kaloper🇺🇸 · Antonio Padilla🇬🇧 · David Stefanyszyn🇬🇧

    We consider phase transitions and their contributions to vacuum energy in the manifestly local theory of vacuum energy sequestering. We demonstrate that the absence of instabilities imposes constraints on the couplings of gravitating and non-gravitating sectors, which can be satisfied in a large class of models. We further show by explicit construction that the vacuum energy contributions to the effective cosmological constant in the descendant vacua are generically strongly suppressed by the ratios of spacetime volumes of parent and descendant geometries. This means that the cosmological constant in de Sitter descendant vacua remains insensitive to phase transitions which may have occurred in the course of its cosmic history.

    ↳ hep-thastro-ph.COgr-qchep-phPRD(2016)·30 citations
15. 15*

    Highly compact neutron stars in scalar-tensor theories of gravity: Spontaneous scalarization versus gravitational collapse

    Raissa F. P. Mendes🇨🇦 · Néstor Ortiz🇨🇦

    Scalar-tensor theories of gravity are extensions of General Relativity (GR) including an extra, nonminimally coupled scalar degree of freedom. A wide class of these theories, albeit indistinguishable from GR in the weak field regime, predicts a radically different phenomenology for neutron stars, due to a nonperturbative, strong-field effect referred to as spontaneous scalarization. This effect is known to occur in theories where the effective linear coupling ${\beta }_0$ between the scalar and matter fields is sufficiently negative, i.e. ${\beta }_0\lesssim -4.35$, and has been strongly constrained by pulsar timing observations. In the test-field approximation, spontaneous scalarization manifests itself as a tachyonic-like instability. Recently, it was argued that, in theories where ${\beta }_0>0$, a similar instability would be triggered by sufficiently compact neutron stars obeying realistic equations of state. In this work we investigate the endstate of this instability for some representative coupling functions with ${\beta }_0>0$. This is done both through an energy balance analysis of the existing equilibrium configurations, and by numerically determining the nonlinear Cauchy development of unstable initial data. We find that, contrary to the ${\beta }_0<0$ case, the final state of the instability is highly sensitive to the details of the coupling function, varying from gravitational collapse to spontaneous scalarization. In particular, we show, for the first time, that spontaneous scalarization can happen in theories with ${\beta }_0>0$, which could give rise to novel astrophysical tests of the theory of gravity.

    ↳ gr-qcastro-ph.HEhep-phPRD(2016)·94 citations
16. 16*

    Dark energy as the weight of violating energy conservation

    Thibaut Josset🇫🇷 · Alejandro Perez🇫🇷 · Daniel Sudarsky🇲🇽

    In this letter, we consider the possibility of reconciling metric theories of gravitation with violation of the conservation of energy-momentum. Under some circumstances, this can be achieved in the context of unimodular gravity, and it leads to the emergence of an effective cosmological constant in Einstein's equation. We specifically investigate two potential sources of energy non-conservation ---non-unitary modifications of quantum mechanics, and phenomenological models motivated by quantum gravity theories with spacetime discreteness at the Planck scale--- and show that such locally negligible phenomena can nevertheless become relevant at the cosmological scale.

    ↳ gr-qcastro-ph.COhep-phhep-th+1PRL(2017)·202 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.