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New Higgs Inflation in a No-Scale Supersymmetric SU(5) GUT
https://cds.cern.ch/record/1971489
Higgs inflation is attractive because it identifies the inflaton with the electroweak Higgs boson. In this work, we construct a new class of supersymmetric Higgs inflationary models in the no-scale supergravity with an SU(5) GUT group. Extending the no-scale Kahler potential and SU(5) GUT superpotential, we derive a generic potential for Higgs inflation that includes the quadratic monomial potential and a Starobinsky-type potential as special limits. This type of models can accommodate a wide range of the tensor-to-scalar ratio $r = O(10^{-3}-10^{-1})$, as well as a scalar spectral index $n_s \sim 0.96$.Ellis, JohnHe, Hong-JianXianyu, Zhong-ZhiTue, 25 Nov 2014 11:23:37 GMT20 Nov 2014arXiv:1411.5537https://cds.cern.ch/record/1971489On the two-loop corrections to the Higgs masses in the NMSSM
https://cds.cern.ch/record/1970735
We discuss the impact of the two-loop corrections to the Higgs mass in the NMSSM beyond $O(\alpha_S(\alpha_b + \alpha_t))$. For this purpose we use the combination of the public tools SARAH and SPheno to include all contributions stemming from superpotential parameters. We show that the corrections in the case of a heavy singlet are often MSSM-like and reduce the predicted mass of the SM-like state by about 1 GeV as long as $\lambda$ is moderately large. For larger values of $\lambda$ the additional corrections can increase the SM-like Higgs mass. If a light singlet is present the additional corrections become more important even for smaller values of $\lambda$ and can even dominate the ones involving the strong interaction. In this context we point out that important effects are not reproduced quantitatively when only including $O((\alpha_b+\alpha_t+\alpha_\tau)^2)$ corrections known from the MSSM.Goodsell, Mark DNickel, KilianStaub, FlorianWed, 19 Nov 2014 08:34:10 GMT17 Nov 2014arXiv:1411.4665https://cds.cern.ch/record/1970735Nonlinear evolution of density and flow perturbations on a Bjorken background
https://cds.cern.ch/record/1969230
Density perturbations and their dynamic evolution from early to late times can be used for an improved understanding of interesting physical phenomena both in cosmology and in the context of heavy-ion collisions. We discuss the spectrum and bispectrum of these perturbations around a longitudinally expanding fireball after a heavy-ion collision. The time-evolution equations couple the spectrum and bispectrum to each other, as well as to higher-order correlation functions through nonlinear terms. A non-trivial bispectrum is thus always generated, even if absent initially. For initial conditions corresponding to a model of independent sources, we discuss the linear and nonlinear evolution is detail. We show that, if the initial conditions are sufficiently smooth for fluid dynamics to be applicable, the nonlinear effects are relatively small.Brouzakis, NikolaosFloerchinger, StefanTetradis, NikolaosWiedemann, Urs AchimThu, 13 Nov 2014 06:52:35 GMT11 Nov 2014arXiv:1411.2912https://cds.cern.ch/record/1969230Accelerating cosmological expansion from shear and bulk viscosity
https://cds.cern.ch/record/1969160
The dissipation of energy from local velocity perturbations in the cosmological fluid affects the time evolution of spatially averaged fluid dynamic fields and the cosmological solution of Einstein's field equations. We show how this backreaction effect depends on shear and bulk viscosity and other material properties of the dark sector, as well as the spectrum of perturbations. If sufficiently large, this effect could account for the acceleration of the cosmological expansion.Floerchinger, StefanTetradis, NikolaosWiedemann, Urs AchimThu, 13 Nov 2014 06:49:20 GMT11 Nov 2014arXiv:1411.3280https://cds.cern.ch/record/1969160Why should we care about the top quark Yukawa coupling?
https://cds.cern.ch/record/1968356
In the cosmological context, for the Standard Model to be valid up to the scale of inflation, the top quark Yukawa coupling $y_t$ should not exceed the critical value $y_t^{crit}$, coinciding with good precision (about 0.02%) with the requirement of the stability of the electroweak vacuum. So, the exact measurements of $y_t$ may give an insight on the possible existence and the energy scale of new physics above 100 GeV, which is extremely sensitive to $y_t$. We overview the most recent theoretical computations of $y_t^{crit}$ and the experimental measurements of $y_t$. Within the theoretical and experimental uncertainties in $y_t$ the required scale of new physics varies from $10^7$ GeV to the Planck scale, urging for precise determination of the top quark Yukawa coupling.Bezrukov, FedorShaposhnikov, MikhailTue, 11 Nov 2014 07:12:08 GMT07 Nov 2014arXiv:1411.1923https://cds.cern.ch/record/1968356Approach to equilibrium in weakly coupled nonabelian plasmas
https://cds.cern.ch/record/1967245
We follow the time evolution of nonabelian gauge bosons from far-from-equilibrium initial conditions to thermal equilibrium by numerically solving an effective kinetic equation that becomes accurate in the weak coupling limit. We consider initial conditions that are either highly overoccupied or underoccupied. We find that overoccupied systems thermalize through a turbulent cascade reaching equilibrium in multiples of a thermalization time $t\approx 72./ (1-0.12\log \lambda)/\lambda^2 T$, whereas underoccupied systems undergo a "bottom-up" thermalization in a time $t\approx (34. +21. \ln(Q/T))/ (1-0.037\log \lambda)(Q/T)^{1/2}/\lambda^2 T$, where $Q$ is the characteristic momentum scale of the initial condition. We apply this result to model initial stages of heavy-ion collisions and find rapid thermalization roughly in a time $Qt \lesssim 10$ or $t\lesssim 1$ fm/c.Kurkela, AleksiLu, EgangThu, 06 Nov 2014 07:31:59 GMT24 May 2014arXiv:1405.6318https://cds.cern.ch/record/1967245TEK twisted gradient flow running coupling
https://cds.cern.ch/record/1966814
We measure the running of the twisted gradient flow coupling in the Twisted Eguchi-Kawai (TEK) model, the SU(N) gauge theory on a single site lattice with twisted boundary conditions in the large N limit.Pérez, Margarita GarcíaGonzález-Arroyo, AntonioKeegan, LiamOkawa, MasanoriTue, 04 Nov 2014 06:37:44 GMT02 Nov 2014arXiv:1411.0258https://cds.cern.ch/record/1966814Exploring CP Violation in the MSSM
https://cds.cern.ch/record/1956033
We explore the prospects for observing CP violation in the minimal supersymmetric extension of the Standard Model (MSSM) with six CP-violating parameters, three gaugino mass phases and three phases in trilinear soft supersymmetry-breaking parameters, using the CPsuperH code combined with a geometric approach to maximize CP-violating observables subject to the experimental upper bounds on electric dipole moments. We also implement CP-conserving constraints from Higgs physics, flavour physics and the upper limits on the cosmological dark matter density and spin-independent scattering. We study possible values of observables within the constrained MSSM (CMSSM), the non-universal Higgs model (NUHM), the CPX scenario and a variant of the phenomenological MSSM (pMSSM). We find values of the CP-violating asymmetry A_CP in b -> s gamma decay that may be as large as 3%, so future measurements of A_CP may provide independent information about CP violation in the MSSM. We find that CP-violating MSSM contributions to the B_s meson mass mixing term Delta M_Bs are in general below the present upper limit, which is dominated by theoretical uncertainties. If these could be reduced, Delta M_Bs could also provide an interesting and complementary constraint on the six CP-violating MSSM phases, enabling them all to be determined experimentally, in principle. We also find that CP violation in the h_{2,3} tau+ tau- and h_{2,3} tbar t couplings can be quite large, and so may offer interesting prospects for future pp, e+ e-, mu+ mu- and gamma gamma colliders.Arbey, AEllis, JGodbole, R MMahmoudi, FMon, 20 Oct 2014 06:00:34 GMT17 Oct 2014arXiv:1410.4824https://cds.cern.ch/record/1956033Global fits to b -> s ll data and signs for lepton non-universality
https://cds.cern.ch/record/1955758
There are some slight tensions with the SM predictions within the latest LHCb measurements. Besides the known anomaly in one angular observable of the rare decay B -> K* mu+ mu-, another small discrepancy recently occurred. The ratio R_K = BR(B+ -> K+ mu+ mu-) / BR(B+ -> K+ e+ e-) in the low-q^2 region has been measured by LHCb showing a 2.6 sigma deviation from the SM prediction. In contrast to the anomaly in the rare decay B -> K* mu+ mu- which is affected by power corrections, the ratio R_K is theoretically rather clean. We analyse all the b -> s ll data with global fits and in particular explore the possibility of breaking of lepton universality. Possible cross-checks with an analysis of the inclusive B -> X_s l+ l- decay are also explored.Hurth, TMahmoudi, FNeshatpour, SFri, 17 Oct 2014 05:43:19 GMT16 Oct 2014arXiv:1410.4545https://cds.cern.ch/record/1955758Completing Lorentz violating massive gravity at high energies
https://cds.cern.ch/record/1954361
Theories with massive gravitons are interesting for a variety of physical applications, ranging from cosmological phenomena to holographic modeling of condensed matter systems. To date, they have been formulated as effective field theories with a cutoff proportional to a positive power of the graviton mass m_g and much smaller than that of the massless theory (M_P ~ 10^19 GeV in the case of general relativity). In this paper we present an ultraviolet completion for massive gravity valid up to a high energy scale independent of the graviton mass. The construction is based on the existence of a preferred time foliation combined with spontaneous condensation of vector fields. The perturbations of these fields are massive and below their mass the theory reduces to a model of Lorentz violating massive gravity. The latter theory possesses instantaneous modes whose consistent quantization we discuss in detail. We briefly study some modifications to gravitational phenomenology at low-energies. The homogeneous cosmological solutions are the same as in the standard cosmology. The gravitational potential of point sources agrees with the Newtonian one at distances small with respect to m_g^(-1). Interestingly, it becomes repulsive at larger distances.Blas, DiegoSibiryakov, SergeySat, 11 Oct 2014 05:26:59 GMT09 Oct 2014arXiv:1410.2408https://cds.cern.ch/record/1954361Lattice gauge theory without link variables
https://cds.cern.ch/record/1951631
We obtain a sequence of alternative representations for the partition function of pure SU(N) or U(N) lattice gauge theory with the Wilson plaquette action, using the method of Hubbard-Stratonovich transformations. In particular, we are able to integrate out all the link variables exactly, and recast the partition function of lattice gauge theory as a Gaussian integral over auxiliary fields.Vairinhos, Helviode Forcrand, PhilippeThu, 02 Oct 2014 05:59:42 GMT30 Sep 2014arXiv:1409.8442https://cds.cern.ch/record/1951631Natural Braneworld Inflation in Light of Recent Results from Planck and BICEP2
https://cds.cern.ch/record/1951523
In this paper we report on a major theoretical observation in cosmology. We present a concrete cosmological model for which inflation has natural beginning and natural ending. Inflation is driven by a cosine-form potential, $V(\phi)= \Lambda^4 (1-\cos(\phi/f))$, which begins at $\phi \lesssim \pi f$ and ends at $\phi =\phi_{\text{end}} \lesssim 5 f/3$. The distance traversed by the inflaton field $\phi$ is sub-Planckian. The Gauss-Bonnet term ${\cal R}^2$ arising as leading curvature corrections in the action $S = \int d^5{x} \sqrt{-g_{5}} M^3 (- 6\lambda M^2 + R + \alpha M^{-2} {\cal R}^2)+ \int d^{4}x \sqrt{-g_{4}} (\dot{\phi}^2/2 - V(\phi)- \sigma +{\cal L}_{\text{matter}})$ (where $\alpha$ and $\lambda$ are constants and $M$ is the five-dimensional Planck mass) plays a key role to terminate inflation. The model generates appropriate tensor-to-scalar ratio $r$ and inflationary perturbations that are consistent with results from Planck and BICEP2. For example, for $N_*= 50-60$ and $n_s\sim 0.960\pm 0.005$, the model predicts that $M\sim 5.64\times 10^{16}\,{\text{GeV}}$ and $r\sim (0.14-0.21)$ [$N_*$ is the number of {\it e}--folds of inflation and $n_s$ ($n_{t}$) is the scalar (tensor) spectrum spectral index]. The ratio $-n_t/r$ is (13% -- 24%) less than its value in 4D Einstein gravity, $-n_t/r=1/8$. The upper bound on the energy scale of inflation $V^{1/4}=2.37\times 10^{16}\,{\text{GeV}}$ ($r<0.27$) implies that $(-\lambda \alpha) \gtrsim 75 \times 10^{-5}$ and $\Lambda<2.17\times 10^{16}\,{\text{GeV}}$, which thereby rule out the case $\alpha=0$ (Randall-Sundrum model). The true nature of gravity is holographic as implied by braneworld realization of string and M theory. The model correctly predicts a late epoch cosmic acceleration with the dark energy equation of state ${\text w}_{\text{DE}}\approx -1$.Neupane, Ishwaree PThu, 02 Oct 2014 05:56:32 GMT29 Sep 2014arXiv:1409.8647https://cds.cern.ch/record/1951523Exact correlation functions in SU(2) N=2 superconformal QCD
https://cds.cern.ch/record/1756059
We report an exact solution of 2- and 3-point functions of chiral primary fields in SU(2) N=2 super-Yang-Mills theory coupled to four hypermultiplets. It is shown that these correlation functions are non-trivial functions of the gauge coupling, obeying differential equations which take the form of the semi-infinite Toda chain. We solve these equations recursively in terms of the Zamolodchikov metric that can be determined exactly from supersymmetric localization on the four-sphere. Our results are verified independently in perturbation theory with a Feynman diagram computation up to 2-loops. This is a short version of a companion paper that contains detailed technical remarks, additional material and aspects of an extension to SU(N) gauge group.Baggio, MarcoNiarchos, VasilisPapadodimas, KyriakosWed, 17 Sep 2014 05:54:39 GMT15 Sep 2014arXiv:1409.4217https://cds.cern.ch/record/1756059Ambient cosmology and spacetime singularities
https://cds.cern.ch/record/1754677
We present a new approach to the issues of spacetime singularities and cosmic censorship in general relativity. This is based on the idea that standard 4-dimensional spacetime is the conformal infinity of an ambient metric for the 5-dimensional Einstein equations with fluid sources. We then find that the existence of spacetime singularities in four dimensions is constrained by asymptotic properties of the ambient 5-metric, while the non-degeneracy of the latter crucially depends on cosmic censorship holding on the boundary.Antoniadis, IgnatiosCotsakis, SpirosWed, 10 Sep 2014 05:35:18 GMT08 Sep 2014arXiv:1409.2220https://cds.cern.ch/record/1754677A Cheap Alternative to the Lattice?
https://cds.cern.ch/record/1754001
We show how to perform accurate, nonperturbative and controlled calculations in quantum field theory in d dimensions. We use the Truncated Conformal Space Approach (TCSA), a Hamiltonian method which exploits the conformal structure of the UV fixed point. The theory is regulated in the IR by putting it on a sphere of a large finite radius. The QFT Hamiltonian is expressed as a matrix in the Hilbert space of CFT states. After restricting ourselves to energies below a certain UV cutoff, an approximation to the spectrum is obtained by numerical diagonalization of the resulting finite-dimensional matrix. The cutoff dependence of the results can be computed and efficiently reduced via a renormalization procedure. We work out the details of the method for the phi^4 theory in d dimensions with d not necessarily integer. A numerical analysis is then performed for the specific case d = 2.5, a value chosen in the range where UV divergences are absent. By going from weak to intermediate to strong coupling, we are able to observe the symmetry-preserving, symmetry-breaking, and conformal phases of the theory, and perform rough measurements of masses and critical exponents. As a byproduct of our investigations we find that both the free and the interacting theories in non integral d are not unitary, which however does not seem to cause much effect at low energies.Hogervorst, MatthijsRychkov, Slavavan Rees, Balt CMon, 08 Sep 2014 05:25:58 GMT04 Sep 2014arXiv:1409.1581https://cds.cern.ch/record/1754001Cosmic backgrounds of relic gravitons and their absolute normalization
https://cds.cern.ch/record/1752916
Provided the consistency relations are not violated, the recent Bicep2 observations pin down the absolute normalization, the spectral slope and the maximal frequency of the cosmic graviton background produced during inflation. The properly normalized spectra are hereby computed from the lowest frequencies (of the order of the present Hubble rate) up to the highest frequency range in the GHz region. Deviations from the conventional paradigm cannot be excluded and are examined by allowing for different physical possibilities including, in particular, a running of the tensor spectral index, an explicit breaking of the consistency relations and a spike in the high-frequency tail of the spectrum coming either from a post-inflationary phase dominated by a stiff fluid of from the contribution of waterfall fields in a hybrid inflationary context. The direct determinations of the tensor to scalar ratio at low frequencies, if confirmed by the forthcoming observations, will also affect and constrain the high-frequencies uncertainties. The limits on the cosmic graviton backgrounds coming from wide-band interferometers (such as Ligo/Virgo, Lisa and Bbo/Decigo) together with a more accurate scrutiny of the tensor B mode polarization at low frequencies will set direct bounds on the post-inflationary evolution and on other unconventional completions of the standard lore.Giovannini, MassimoTue, 02 Sep 2014 05:23:37 GMT24 May 2014arXiv:1405.6301https://cds.cern.ch/record/1752916Catching sparks from well-forged neutralinos
https://cds.cern.ch/record/1752392
In this paper we present a new search technique for electroweakinos, the superpartners of electroweak gauge and Higgs bosons, based on final states with missing transverse energy, a photon, and a dilepton pair, $\ell^+\,\ell^- + \gamma + \displaystyle{\not} E_T$. Unlike traditional electroweakino searches, which perform best when $m_{\widetilde{\chi}^0_{2,3}} - m_{\widetilde{\chi}^0_1}, m_{\widetilde{\chi}^{\pm}} - m_{\widetilde{\chi}^0_1} > m_Z$, our search favors nearly degenerate spectra; degenerate electroweakinos typically have a larger branching ratio to photons, and the cut $m_{\ell\ell} \ll m_Z$ effectively removes on-shell Z boson backgrounds while retaining the signal. This feature makes our technique optimal for `well-tempered' scenarios, where the dark matter relic abundance is achieved with inter-electroweakino splittings of $\sim 20 - 70\,\text{GeV}$. Additionally, our strategy applies to a wider range of scenarios where the lightest neutralinos are almost degenerate, but only make up a subdominant component of the dark matter -- a spectrum we dub `well-forged'. Focusing on bino-Higgsino admixtures, we present optimal cuts and expected efficiencies for several benchmark scenarios. We find bino-Higgsino mixtures with $m_{\widetilde{\chi}^0_{2,3}} \lesssim 190\,\text{GeV}$ and $m_{\widetilde{\chi}^0_{2,3}} - m_{\widetilde{\chi}^0_1} \cong 30\,\text{GeV}$ can be uncovered after roughly $600\,\text{fb}^{-1}$ of luminosity at the 14 TeV LHC. Scenarios with lighter states require less data for discovery, while scenarios with heavier states or larger mass splittings are harder to discriminate from the background and require more data. Unlike many searches for supersymmetry, electroweakino searches are one area where the high luminosity of the next LHC run, rather than the increased energy, is crucial for discovery.Bramante, JosephDelgado, AntonioElahi, FatemehMartin, AdamOstdiek, BryanFri, 29 Aug 2014 05:38:53 GMT27 Aug 2014arXiv:1408.6530https://cds.cern.ch/record/1752392Gauss-Bonnet assisted braneworld inflation in light of BICEP2 and Planck data
https://cds.cern.ch/record/1752311
Motivated by the idea that quantum gravity corrections usually suppress the power of the scalar primordial spectrum (E-mode) more than the power of the tensor primordial spectrum (B-mode), in this paper we construct a concrete gravitational theory in five-dimensions for which $V(\phi)\propto \phi^n$-type inflation ($n\ge 1$) generates an appropriate tensor-to-scalar ratio that may be compatible with the BICEP2 and Planck data together. The true nature of gravity is five-dimensional and described by the action $S = \int d^5{x} \sqrt{|g|} M^3 (- 6\lambda M^2 + R + \alpha M^{-2} {\cal R}^2)$ where $M$ is the five-dimensional Planck mass and ${\cal R}^2=R^2-4 R_{ab} R^{ab} + R_{abcd} R^{abcd}$ is the Gauss-Bonnet (GB) term. The five-dimensional "bulk" spacetime is anti-de Sitter ($\lambda<0$) for which inflation ends naturally. The effects of ${\cal R}^2$ term on the magnitudes of scalar and tensor fluctuations and spectral indices are shown to be important at the energy scale of inflation. For GB-assisted $m^2\phi^2$-inflation, inflationary constraints from BICEP2 and Planck, such as, $n_s\simeq 0.9603 (\pm 0.0073)$, $r=0.16 (+0.06-0.05)$ and $V_*^{1/4} \sim 1.5\times 10^{16} {\text GeV}$ are all satisfied for $ (-\lambda \alpha) \simeq (3-300)\times 10^{-5}$.Neupane, Ishwaree PFri, 29 Aug 2014 05:36:20 GMT27 Aug 2014arXiv:1408.6613https://cds.cern.ch/record/1752311SIMPle Dark Matter: Self-Interactions and keV Lines
https://cds.cern.ch/record/1752287
We consider a simple supersymmetric hidden sector: pure SU(N) gauge theory. Dark matter is made up of hidden glueballinos with mass $m_X$ and hidden glueballs with mass near the confinement scale $\Lambda$. For $m_X \sim 1~\text{TeV}$ and $\Lambda \sim 100~\text{MeV}$, the glueballinos freeze out with the correct relic density and self-interact through glueball exchange to resolve small-scale structure puzzles. An immediate consequence is that the glueballino spectrum has a hyperfine splitting of order $\Lambda^2 / m_X \sim 10~\text{keV}$. We show that the radiative decays of the excited state can explain the observed 3.5 keV X-ray line signal from clusters of galaxies, Andromeda, and the Milky Way.Boddy, Kimberly KFeng, Jonathan LKaplinghat, ManojShadmi, YaelTait, Timothy M PFri, 29 Aug 2014 05:36:18 GMT27 Aug 2014arXiv:1408.6532https://cds.cern.ch/record/1752287W gamma production in hadronic collisions using the POWHEG+MiNLO method
https://cds.cern.ch/record/1751762
We detail a calculation of W gamma production in hadronic collision, at Next-to-Leading Order (NLO) QCD interfaced to a shower generator according to the POWHEG prescription supplemented with the MiNLO procedure. The fixed order result is matched to an interleaved QCD+QED parton shower, in such a way that the contribution arising from hadron fragmentation into photons is fully modeled. In general, our calculation illustrates a new approach to the fully exclusive simulation of prompt photon production processes accurate at the NLO level in QCD. We compare our predictions to those of the NLO program MCFM, which treats the fragmentation contribution in terms of photon fragmentation functions. We also perform comparisons to available LHC data at 7 TeV, for which we observe good agreement, and provide phenomenological results for physics studies of the W gamma production process at the Run II of the LHC. The new tool, which includes W leptonic decays and the contribution of anomalous gauge couplings, allows a fully exclusive, hadron-level description of the W gamma process, and is publicly available at the repository of the POWHEG BOX. Our approach can be easily adapted to deal with other relevant isolated photon production processes in hadronic collisions.Barze, LucaChiesa, MauroMontagna, GuidoNason, PaoloNicrosini, OrestePiccinini, FulvioProsperi, ValeriaTue, 26 Aug 2014 05:52:59 GMT25 Aug 2014arXiv:1408.5766https://cds.cern.ch/record/1751762On the Flavor Structure of Natural Composite Higgs Models & Top Flavor Violation
https://cds.cern.ch/record/1751232
We explore the up flavor structure of composite pseudo Nambu-Goldstone-boson Higgs models, where we focus on the flavor anarchic minimal $SO(5)$ case. We identify the different sources of flavor violation in this framework and emphasise the differences from the anarchic Randall-Sundrum scenario. In particular, the fact that the flavor symmetry does not commute with the symmetries that stabilize the Higgs potential may constrain the flavor structure of the theory. In addition, we consider the interplay between the fine tuning of the model and flavor violation. We find that generically the tuning of this class of models is worsen in the anarchic case due to the contributions from the additional fermion resonances. We show that, even in the presence of custodial symmetry, large top flavor violating rate are naturally expected. In particular, $t\to cZ$ branching ratio of order of $10^{-5}$ is generic for this class of models. Thus, this framework can be tested in the next run of the LHC as well as in other future colliders. We also find that the top flavor violation is weakly correlated with the increase amount of fine tuning. Finally, other related flavor violation effects, such as $t \to ch$ and in the $D$ system, are found to be too small to be observed by the current and near future colliders.Azatov, AleksandrPanico, GiulianoPerez, GiladSoreq, YotamFri, 22 Aug 2014 08:14:03 GMT20 Aug 2014arXiv:1408.4525https://cds.cern.ch/record/1751232The chiral phase transition in two-flavor QCD from imaginary chemical potential
https://cds.cern.ch/record/1751225
We investigate the order of the finite temperature chiral symmetry restoration transition for QCD with two massless fermions, by using a novel method, based on simulating imaginary values of the quark chemical potential $\mu=i\mu_i,\mu_i\in\mathbb{R}$. Our method exploits the fact that, for low enough quark mass $m$ and large enough chemical potential $\mu_i$, the chiral transition is decidedly first order, then turning into crossover at a critical mass $m_c(\mu)$. It is thus possible to determine the critical line in the $m - \mu^2$ plane, which can be safely extrapolated to the chiral limit by taking advantage of the known tricritical indices governing its shape. We test this method with standard staggered fermions and the result of our simulations is that $m_c(\mu=0)$ is positive, so that the phase transition at zero density is definitely first order in the chiral limit, on our coarse $N_t=4$ lattices with $a\simeq 0.3\,\mathrm{fm}$.Bonati, Claudiode Forcrand, PhilippeD'Elia, MassimoPhilipsen, OweSanfilippo, FrancescoFri, 22 Aug 2014 08:13:11 GMT21 Aug 2014arXiv:1408.5086https://cds.cern.ch/record/1751225Dark matter direct detection constraints from gauge bosons loops
https://cds.cern.ch/record/1751207
While many interactions of dark matter (DM) with the standard model (SM) affect direct detection and LHC searches, there are only a few operators generating annihilation of DM into photons. All of these operators, except four of them, give rise to unsuppressed rates, rendering indirect detection superior to other search strategies. For two of the four effective interactions with velocity-suppressed annihilation cross sections, we identify a new type of loop effect which significantly enhances the associated direct detection rates. As a result, relevant constraints from next-generation direct detection experiments on DM-SM interactions, so far only bounded by the LHC, are obtained.Crivellin, AndreasHaisch, UlrichFri, 22 Aug 2014 06:26:30 GMT21 Aug 2014arXiv:1408.5046https://cds.cern.ch/record/1751207Muon g-2 Anomaly and Dark Leptonic Gauge Boson
https://cds.cern.ch/record/1750835
One of the major motivations to search for a dark gauge boson of MeV-GeV scale is the long-standing muon g-2 anomaly. Because of active searches such as fixed target experiments and rare meson decays, the muon g-2 favored parameter region has been rapidly reduced. With the most recent data, it is practically excluded now in the popular dark photon model. We overview the issue and investigate a potentially alternative model based on the gauged lepton number or U(1)_L. The muon g-2 favored parameter region of the U(1)_L survives all the constraints that were critical in the dark photon case, yet it is disfavored by the new constraints from the large flux neutrino experiments.Lee, Hye-SungWed, 20 Aug 2014 05:34:22 GMT19 Aug 2014arXiv:1408.4256https://cds.cern.ch/record/1750835Gravity and axions from a random UV QFT
https://cds.cern.ch/record/1750573
It is postulated that the UV QFT is enormous and random. The coupling of the Standard Model to such QFT is analyzed. It is argued that massless 4d gravity and axions are general avatars of the postulate. The equivalence principle emerges naturally as well as a concrete set of sources for its breaking. The axion scale is related to the 4d Planck scale as $f=M_P/N$, where $N$ is the "number of colors" of the (almost) hidden UV CFT.Kiritsis, EliasTue, 19 Aug 2014 05:40:45 GMT15 Aug 2014arXiv:1408.3541https://cds.cern.ch/record/1750573