arXiv subjects

Martti Raidal

Publications and source records attributed to Martti Raidal.

At least 91 records · Page 5Linked to original sources

arXiv2015

A new mechanism for dark energy: the adaptive screening

We describe how known matter effects within a well-motivated particle physics framework can explain the dark energy component of the Universe. By considering a cold gas of particles which interact via a vector mediator, we show that there exists a regime where the gas reproduces the dynamics of dark energy. In this regime the screening mass of the mediator is proportional to the number density of the gas, hence we refer to this phenomenon as "the adaptive screening mechanism". As an example, we argue that such screening mass can result from strong localization of the vector mediators. The proposed dark energy mechanism could be experimentally verified through cosmological observations by the Euclid experiment, as well as by studying properties of dark photons and sterile neutrinos.

astro-ph.CO↗

arXiv2014

Prospects for constrained supersymmetry at $\sqrt{s}=33$ TeV and $\sqrt{s}=100$ TeV proton-proton super-colliders

Discussions are underway for a high-energy proton-proton collider. Two preliminary ideas are the $\sqrt{s}=33$ TeV HE-LHC and the $\sqrt{s}=100$ TeV VLHC. With Bayesian statistics, we calculate the probabilities that the LHC, HE-LHC and VLHC discover SUSY in the future, assuming that nature is described by the CMSSM and given the experimental data from the LHC, LUX and Planck. We find that the LHC with $300$/fb at $\sqrt{s}=14$ TeV has a $15$-$75%$ probability of discovering SUSY. Should that run fail to discover SUSY, the probability of discovering SUSY with $3000$/fb is merely $1$-$10%$. Were SUSY to remain undetected at the LHC, the HE-LHC would have a $35$-$85%$ probability of discovering SUSY with $3000$/fb. The VLHC, on the other hand, ought to be definitive; the probability of it discovering SUSY, assuming that the CMSSM is the correct model, is $100%$.

hep-ph↗

arXiv2014

Embedding inflation into the Standard Model - more evidence for classical scale invariance

If cosmological inflation is due to a slowly rolling single inflation field taking trans-Planckian values as suggested by the BICEP2 measurement of primordial tensor modes in CMB, embedding inflation into the Standard Model challenges standard paradigm of effective field theories. Together with an apparent absence of Planck scale contributions to the Higgs mass and to the cosmological constant, BICEP2 provides further experimental evidence for the absence of large $M_{\rm P}$ induced operators. We show that classical scale invariance, the paradigm that all fundamental scales in Nature are induced by quantum effects, solves the problem and allows for a remarkably simple scale-free Standard Model extension with inflaton without extending the gauge group. Due to trans-Planckian inflaton values and vevs, a dynamically induced Coleman-Weinberg-type inflaton potential of the model can predict tensor-to-scalar ratio $r$ in a large range, converging around the prediction of chaotic $m^2ϕ^2$ inflation for a large trans-Planckian value of the inflaton vev. Precise determination of $r$ in future experiments will single out a unique scale-free inflation potential, allowing to test the proposed field-theoretic framework.

hep-ph↗

arXiv2014

Dark photons and resonant monophoton signatures in Higgs boson decays at the LHC

Motivated by dark-photon $\barγ$ scenarios extensively considered in the literature, we explore experimentally allowed models where the Higgs boson coupling to photon and dark photon $Hγ\barγ$ can be enhanced. Correspondingly, large rates for the $H\to γ\bar γ$ decay become plausible, giving rise to one monochromatic photon with $E^γ\simeq m_H/2$ (i.e., more than twice the photon energy in the rare standard-model decay $H\to γZ\toγ\barνν$), and a similar amount of missing energy. We perform a model-independent study of this exotic resonant monophoton signature at the LHC, featuring a distinctive $E^γ_T$ peak around 60 GeV, and $γ+\slashed{E}_T$ transverse invariant mass ruled by $m_H$. At parton level, we find a $5\,σ$ sensitivity of the present LHC data set for a $H\to γ\barγ$ branching fraction of $0.5\%$. Such large branching fractions can be naturally obtained in dark $U(1)_F$ models explaining the origin and hierarchy of the standard model Yukawa couplings. We urge the LHC experiments to search for this new exotic resonance in the present data set, and in future LHC runs.

hep-ph↗

arXiv2014

Testing Right-Handed Currents at the LHC

The CMS Collaboration has published two different searches for new physics that contain possible hints for excesses in $eejj$ and $eνjj$ final states. Interpreting those hints as a possible signal of a right-handed gauge boson $W_R$ with mass 2-2.5~TeV may have profound implications for our understanding of the gauge structure of nature and Grand Unification, the scalar sector accessible at the LHC, neutrino physics, and the baryon asymmetry of the Universe. We show that this interpretation is, indeed, consistent with all existing constraints. However, before making premature claims we propose a number of cross-checks at the LHC14 that could confirm or falsify this scenario. Those include searches for a $Z_R$ resonance and the related new scalar sector around 6-7~TeV. Additionally, large effects in top-quark spin-asymmetries in single top production are possible.

hep-ph↗

arXiv2014

The universal Higgs fit

We perform a state-of-the-art global fit to all Higgs data. We synthesise them into a 'universal' form, which allows to easily test any desired model. We apply the proposed methodology to extract from data the Higgs branching ratios, production cross sections, couplings and to analyse composite Higgs models, models with extra Higgs doublets, supersymmetry, extra particles in the loops, anomalous top couplings, invisible Higgs decay into Dark Matter. Best fit regions lie around the Standard Model predictions and are well approximated by our 'universal' fit. Latest data exclude the dilaton as an alternative to the Higgs, and disfavour fits with negative Yukawa couplings. We derive for the first time the SM Higgs boson mass from the measured rates, rather than from the peak positions, obtaining $M_h = 125.0 \pm 1.8$ GeV.

hep-ph↗

arXiv2014

Physical Naturalness and Dynamical Breaking of Classical Scale Invariance

We propose a model of a confining dark sector, dark technicolor, that communicates with the Standard Model through the Higgs portal. In this model electroweak symmetry breaking and dark matter share a common origin, and the electroweak scale is generated dynamically. Our motivation to suggest this model is the absense of evidence for new physics from recent LHC data. Although the conclusion is far from certain at this point, this lack of evidence may suggest that no mechanism exists at the electroweak scale to stabilise the Higgs mass against radiative corrections from UV physics. The usual reaction to this puzzling situation is to conclude that the stabilising new physics is either hidden from us by accident, or that it appears at energies that are currently inaccessible, such that nature is indeed fine-tuned. In order to re-examine the arguments that have lead to this dichotomy, we review the concept of naturalness in effective field theories, discussing in particular the role of quadratic divergences in relation to different energy scales. This leads us to suggest classical scale invariance as a guidline for model building, implying that explicit mass scales are absent in the underlying theory.

hep-ph↗

arXiv2014

Minimal semi-annihilating $\mathbb{Z}_N$ scalar dark matter

We study the dark matter from an inert doublet and a complex scalar singlet stabilized by $\mathbb{Z}_N$ symmetries. This field content is the minimal one that allows dimensionless semi-annihilation couplings for $N > 2$. We consider explicitly the $\mathbb{Z}_3$ and $\mathbb{Z}_4$ cases and take into account constraints from perturbativity, unitarity, vacuum stability, necessity for the electroweak $\mathbb{Z}_N$ preserving vacuum to be the global minimum, electroweak precision tests, upper limits from direct detection and properties of the Higgs boson. Co-annihilation and semi-annihilation of dark sector particles as well as dark matter conversion significantly modify the cosmic abundance and direct detection phenomenology.

hep-ph↗

arXiv2014

Towards Completing the Standard Model: Vacuum Stability, EWSB and Dark Matter

We study the standard model (SM) in its full perturbative validity range between $Λ_QCD$ and the $U(1)_Y$ Landau pole, assuming that a yet unknown gravitational theory in the UV does not introduce additional particle thresholds, as suggested by the tiny cosmological constant and the absence of new stabilising physics at the EW scale. We find that, due to dimensional transmutation, the SM Higgs potential has a global minimum at 10^26 GeV, invalidating the SM as a phenomenologically acceptable model in this energy range. We show that extending the classically scale invariant SM with one complex singlet scalar S allows us to: (i) stabilise the SM Higgs potential; (ii) induce a scale in the singlet sector via dimensional transmutation that generates the negative SM Higgs mass term via the Higgs portal; (iii) provide a stable CP-odd singlet as the thermal relic dark matter due to CP-conservation of the scalar potential; (iv) provide a degree of freedom that can act as an inflaton in the form of the CP-even singlet. The logarithmic behaviour of dimensional transmutation allows one to accommodate the large hierarchy between the electroweak scale and the Landau pole, while understanding the latter requires a new non-perturbative view on the SM.

hep-ph↗

arXiv2013

Exponentially spread dynamical Yukawa couplings from non-perturbative chiral symmetry breaking in the dark sector

We propose a new paradigm for generating exponentially spread standard model Yukawa couplings from a new $U(1)_F$ gauge symmetry in the dark sector. Chiral symmetry is spontaneously broken among dark fermions that obtain non-vanishing masses from a non-perturbative solution to the mass gap equation. The necessary ingredient for this mechanism to work is the existence of higher derivative terms in the dark $U(1)_F$ theory, or equivalently the existence of Lee-Wick ghosts, that (i) allow for a non-perturbative solution to the mass gap equation in the weak coupling regime of the Abelian theory; (ii) induce exponential dependence of the generated masses on dark fermion $U(1)_F$ quantum numbers. The generated flavor and chiral symmetry breaking in the dark sector is transferred to the standard model Yukawa couplings at one loop level via Higgs portal type scalar messenger fields. The latter carry quantum numbers of squarks and sleptons. A new intriguing phenomenology is predicted that could be potentially tested at the LHC, provided the characteristic mass scale of the messenger sector is accessible at the LHC as is suggested by naturalness arguments.

hep-ph↗

arXiv2013

Model-independent implications of the e+, e-, anti-proton cosmic ray spectra on properties of Dark Matter

Taking into account spins, we classify all two-body non-relativistic Dark Matter annihilation channels to the allowed polarization states of Standard Model particles, computing the energy spectra of the stable final-state particles relevant for indirect DM detection. We study the DM masses, annihilation channels and cross sections that can reproduce the PAMELA indications of an e+ excess consistently with the PAMELA p-bar data and the ATIC/PPB-BETS e++e- data. From the PAMELA data alone, two solutions emerge: (i) either the DM particles that annihilate into W,Z,h must be heavier than about 10 TeV or (ii) the DM must annihilate only into leptons. Thus in both cases a DM particle compatible with the PAMELA excess seems to have quite unexpected properties. The solution (ii) implies a peak in the e++e- energy spectrum, which, indeed, seems to appear in the ATIC/PPB-BETS data around 700 GeV. If upcoming data from ATIC-4 and GLAST confirm this feature, this would point to a O(1) TeV DM annihilating only into leptons. Otherwise the solution (i) would be favored. We comment on the implications of these results for DM models, direct DM detection and colliders as well as on the possibility of an astrophysical origin of the excess.

hep-ph↗

arXiv2013

Twin Peak Higgs

A broad class of models in which electroweak symmetry breaking originates from dynamics in a singlet dark sector, and is transferred to the Standard Model via the Higgs portal, predicts in general strongly suppressed Higgs boson mixing with a singlet scalar. In this work we point out that at present this class of models allows for the second phenomenologically acceptable solution with almost maximal mixing between the Higgs and the scalar singlet. This scenario predicts an almost degenerate twin peak Higgs signal which is presently indistinguishable from a single peak, due to the limited LHC mass resolution. Because of that, the LHC experiments measure inclusive Higgs rates that all must exactly agree with Standard Model predictions due to sum rules. We show that if the dark sector and Standard Model communicate only via the singlet messenger scalar that mixes with the Higgs, the spin independent direct detection cross section of dark matter is suppressed by the scalar mass degeneracy, explaining its non-observation so far.

hep-ph↗

arXiv2013

Dark Supersymmetry

We propose a model of Dark Supersymmetry, where a supersymmetric dark sector is coupled to the classically scale invariant non-supersymmetric Standard Model through the Higgs portal. The dark sector contains a mass scale that is protected against radiative corrections by supersymmetry, and the portal coupling mediates this scale to the Standard Model, resulting in a vacuum expectation value for the Higgs field and the usual electroweak symmetry breaking mechanism. The supersymmetric dark sector contains dark matter candidates, and we show that the observed dark matter abundance is generated for a natural choice of parameters, while avoiding the current experimental bounds on direct detection. Future experiments can probe this scenario if the dark sector mass scale is not too high.

hep-ph↗

arXiv2013

Fermiophobic Higgs boson and supersymmetry

If a light Higgs boson with mass 125 GeV is fermiophobic, or partially fermiophobic, then the MSSM is excluded. The minimal supersymmetric fermiophobic Higgs scenario can naturally be formulated in the context of the NMSSM that admits Z_3 discrete symmetries. In the fermiophobic NMSSM, the SUSY naturalness criteria are relaxed by a factor N_c y_t^4/g^4 \sim 25, removing the little hierarchy problem and allowing sparticle masses to be naturally of order 2--3 TeV. This scale motivates wino or higgsino dark matter. The SUSY flavour and CP problems as well as the constraints on sparticle and Higgs boson masses from b \to sγ, B_s \to μμ and direct LHC searches are relaxed in fermiophobic NMSSM. The price to pay is that a new, yet unknown, mechanism must be introduced to generate fermion masses. We show that in the fermiophobic NMSSM the radiative Higgs boson branchings to γγ, γZ can be modified compared to the fermiophobic and ordinary standard model predictions, and fit present collider data better. Suppression of dark matter scattering off nuclei explains the absence of signal in XENON100.

hep-ph↗

arXiv2013

$Z_3$ Scalar Singlet Dark Matter

We consider the minimal scalar singlet dark matter stabilised by a $Z_3$ symmetry. Due to the cubic term in the scalar potential, semi-annihilations, besides annihilations, contribute to the dark matter relic density. Unlike in the $Z_2$ case, the dark matter spin independent direct detection cross section is no more linked to the annihilation cross section. We study the extrema of the potential and show that a too large cubic term would break the $Z_3$ symmetry spontaneously, implying a lower bound on the direct detection cross section, and allowing the whole parameter space to be tested by XENON1T. In a small region of the parameter space the model can avoid the instability of the standard model vacuum up to the unification scale. If the semi-annihilations are large, however, new physics will be needed at TeV scale because the model becomes non-perturbative. The singlet dark matter mass cannot be lower than 53.8 GeV due to the constraint from Higgs boson decay into dark matter.

hep-ph↗

arXiv2012

An evidence for indirect detection of dark matter from galaxy clusters in Fermi-LAT data

We search for spectral features in Fermi-LAT gamma-rays coming from regions corresponding to eighteen brightest nearby galaxy clusters determined by the magnitude of their signal line-of-site integrals. We observe a double peak-like excess over the diffuse power-law background at photon energies 110 GeV and 130 GeV with the global statistical significance up to 3.6σ, confirming independently earlier claims of the same excess from Galactic centre. Interpreting this result as a signal of dark matter annihilations to two monochromatic photon channels in galaxy cluster haloes, and fixing the annihilation cross section from the Galactic centre data, we determine the annihilation boost factor due to dark matter subhaloes from data. Our results contribute to discrimination of the dark matter annihilations from astrophysical processes and from systematic detector effects as the possible explanations to the Fermi-LAT excess.

astro-ph.HE↗

arXiv2012

Fermi 130 GeV gamma-ray excess and dark matter annihilation in sub-haloes and in the Galactic centre

We analyze publicly available Fermi-LAT high-energy gamma-ray data and confirm the existence of clear spectral feature peaked at E=130GeV. Scanning over the Galaxy we identify several disconnected regions where the observed excess originates from. Our best optimized fit is obtained for the central region of Galaxy with a clear peak at 130GeV with local statistical significance 4.5 sigma. The observed excess is not correlated with Fermi bubbles. We compute the photon spectra induced by dark matter annihilations into two and four standard model particles, the latter via two light intermediate states, and fit the spectra with data. Since our fits indicate sharper and higher signal peak than in the previous works, data favors dark matter direct two-body annihilation channels into photons or other channels giving only line-like spectra. If Einasto halo profile correctly predicts the central cusp of Galaxy, dark matter annihilation cross-section to two photons is of order ten percent of the standard thermal freeze-out cross-section. The large dark matter two-body annihilation cross-section to photons may signal a new resonance that should be searched for at the CERN LHC experiments.

hep-ph↗

arXiv2012

Anthropic solution to the magnetic muon anomaly: the charged see-saw

We present models of new physics that can explain the muon g-2 anomaly in accord with with the assumption that the only scalar existing at the weak scale is the Higgs, as suggested by anthropic selection. Such models are dubbed "charged see-saw" because the muon mass term is mediated by heavy leptons. The electroweak contribution to the g-2 gets modified by order one factors, giving an anomaly of the same order as the observed hint, which is strongly correlated with a modification of the Higgs coupling to the muon.

hep-ph↗